ABSTRACT Nitrite-oxidizing bacteria (NOB) are important nitrifiers whose activity regulates the availability of nitrite and dictates the magnitude of nitrogen loss in ecosystems. In oxic

marine sediments, ammonia-oxidizing archaea (AOA) and NOB together catalyze the oxidation of ammonium to nitrate, but the abundance ratios of AOA to canonical NOB in some cores are

significantly higher than the theoretical ratio range predicted from physiological traits of AOA and NOB characterized under realistic ocean conditions, indicating that some NOBs are yet to

be discovered. Here we report a bacterial phylum _Candidatus_ Nitrosediminicolota, members of which are more abundant than canonical NOBs and are widespread across global oligotrophic

sediments. Counting _Ca_. Nitrosediminicolota as a nitrite-oxidizer helps to resolve the apparent abundance imbalance between AOA and NOB in oxic marine sediments, and thus its activity may

exert controls on the nitrite budget. SIMILAR CONTENT BEING VIEWED BY OTHERS NITRITE ACCUMULATION AND ANAMMOX BACTERIAL NICHE PARTITIONING IN ARCTIC MID-OCEAN RIDGE SEDIMENTS Article Open

access 29 March 2023 MARINE AMMONIA-OXIDISING ARCHAEA AND BACTERIA OCCUPY DISTINCT IRON AND COPPER NICHES Article Open access 24 March 2021 DYNAMICS OF ACTIVELY DIVIDING PROKARYOTES IN THE

WESTERN MEDITERRANEAN SEA Article Open access 08 February 2022 INTRODUCTION Nitrite is an important intermediate compound in the biogeochemical nitrogen cycle, whose cycling dictates the

availability of fixed nitrogen in marine ecosystems. Nitrite is controlled by multiple metabolic pathways: it can be produced by nitrate reduction and aerobic ammonia oxidation, and consumed

by nitrite reduction and nitrite oxidation1. Among these pathways, by converting nitrite to nitrate, nitrite oxidation is a critical control point retaining bio-available nitrogen in an

ecosystem by limiting the further reduction of nitrite to nitrogen gas2. Nitrite oxidation is mediated by a phylogenetically diverse functional guild known as the nitrite-oxidizing bacteria

(NOB), which has been studied in a range of ecosystems, such as engineered environments3,4, coastal sediments5,6,7, haloalkaline lake sediments8, hot springs9,10,11, seawater12,13, and

oxygen deficient zones14,15. However, the diversity and metabolic capacities of NOB in deep-sea sediments have not been well studied. Nitrification is catalyzed by two different

chemolithoautotrophic guilds, ammonia oxidizers and nitrite oxidizers, and is an important nitrogen cycling process in global marine sediments. Nitrifiers are one of the most dominant

(typically > 10%) functional guilds among the microbial taxa in oxic sediments16,17, which account for a considerable proportion of the global seafloor18. Nitrite rarely accumulates in

such sediments19, where newly produced nitrite is rapidly oxidized to nitrate by NOB due to the presence of oxygen. The absence of appreciable nitrite (and ammonium) in this zone also

indicates that NOBs are as efficient in the oxidation of nitrite as ammonia-oxidizing archaea (AOA) in the oxidation of ammonium released from organic matter degradation, as has been

observed in the dark ocean interior [e.g., see refs. 20,21,22]. For the process of ammonia oxidation in marine sediments, AOA are well known to dominate over ammonia-oxidizing

bacteria16,23,24 and numerous studies have quantified their activity, regulation, power requirement, and genetic identity17,25,26,27,28. By comparison, our knowledge about microorganisms

involved in nitrite oxidation in marine sediments is extremely limited. Previously, gene-based surveys have indicated the presence of _Nitrospinaceae_ and _Nitrospiraceae_ in marine

sediments16,24,29, with a few cultured representatives from coastal sediments5,6,7. However, it remains unclear whether members of _Nitrospinaceae_ and _Nitrospiraceae_ (i.e., the canonical

marine nitrite oxidizers) are in fact the major NOBs in marine sediments. Importantly, NOB abundances in some deep-sea sediments have been observed to be orders of magnitude lower than those

of AOA16,24. This perhaps indicates that the majority of NOB in this vast habitat have not been identified, yet limited case studies exist. If, however, AOA severely outnumber NOB in oxic

marine sediments, the nitrogen cycle would not be closed without a cryptic nitrite loss process, presumably denitrification, that consumes bio-available nitrogen rather than recycling it2.

In this study, we first highlight an abundance mismatch between AOA and canonical NOB in some oxic sediments, based on a compilation of quantitative data in 16 marine sediment cores. To

address this discrepancy, we rely on metagenome sequencing data from the Arctic Mid-Ocean Ridge to discover overlooked NOBs. We focus on three metagenome-assembled genomes (MAGs) that

contain the metabolic potential of nitrite oxidation and form a bacterial phylum different from previously known NOB phyla. We then search for the presence of these novel NOB across global

marine sediments. We conclude by calculating the abundance ratio of AOA to NOB including this more abundant phylum to resolve the previously identified discrepancy. RESULTS AND DISCUSSION

ABUNDANCE MISMATCH BETWEEN AOA AND CANONICAL NOB IN SOME OXIC DEEP-SEA SEDIMENTS In order to investigate the reasons for the often-observed offset between the abundances of AOA and NOB, we

explored the theoretical abundance ratio between them based on their (i) biomass yields (carbon synthesized per nitrogen oxidized) and (ii) cell quotas (mass of carbon per cell), and also

considered (iii) mortality/grazing rates and (iv) relevant environmental conditions. Because AOA and NOB in deep-sea sediments are mostly uncultured, we performed the simple calculation

based on the physiological traits of AOA and NOB isolates grown under relevant oceanic conditions30. Marine AOA exhibit approximately 1.6–3.1 times (mean value 2.3) higher biomass yields

than NOB but maintain only 0.20–0.63 (mean value 0.30) times the cell quota of NOB30. In oxic environments without significant nitrite accumulation, because of the balanced bulk reaction

rates of ammonia and nitrite oxidation, the cell abundance of AOA should be theoretically ~6.9 times (range: 2.6–15.8) higher than that of NOB. The difference in mortality/loss rates20,31

caused by grazing and/or viral lysis has been invoked to explain the relative abundance difference between AOA and NOB in the ocean, although the recent redox-based mechanistic model of

Zakem et al.32 suggests that this is not necessary. Because of the assumed equivalent rates of the tightly coupled ammonia and nitrite oxidation processes, this theoretical ratio is likely

suitable only for predicting the AOA:NOB abundance ratio in well-oxygenated environments without nitrite accumulation, such as oxic sediments and the ocean interior32. Indeed, the 7- to

11-fold abundance differences between AOA and NOB observed in a recent deep ocean compilation32 fall within this theoretical ratio derived from growth characteristic observations. While AOA

and NOB are found in some anoxic [e.g., refs. 31,33,34,35] or fluctuating (e.g., with diel/seasonal variations) environments, under such conditions their metabolic activities are not

necessarily coupled. In anoxic settings, other metabolisms like denitrification can supply and consume nitrite and nitrifiers may engage in other metabolisms36,37, and thus the relative

abundances of AOA and NOB may not be tightly correlated. We tested whether the theoretical AOA:NOB abundance ratio applies in oxic marine sediments. Restricting our analysis to oxic layers,

we focused on a series of deep-sea (depth > 1000 m) sediment cores16,17,38,39,40, in which the thick oxic zones permitted high-resolution profiling of both geochemistry (especially

oxygen) and microbial community composition. We compared the abundances of AOA and NOB, initially assuming that only members of the canonical marine NOB families _Nitrospinaceae_ and

_Nitrospiraceae_ perform nitrite oxidation. In five sediment cores comprising 28 total depth layers from the Atacama Trench40 in the East Pacific Ocean (Supplementary Data 1), we observed a

correlation between the abundances of AOA and NOB, with an AOA:NOB abundance ratio of 10.5 (_R_2 = 0.91, Fig. 1A). That this observed abundance ratio is within the theoretical range,

canonical NOB families likely prevail in the Atacama Trench and novel nitrite oxidizers need not be invoked. However, such an abundance match between AOA and NOB was not always observed in

marine sediments. When extending the comparison to more diverse cores beyond deep trench systems (eight from the Arctic Mid-Ocean Ridge (AMOR) [four cores reported in Zhao et al.38, plus

GS13-CC241, GS14-GC0419, GS14-GC02, and GS15-GC0139], one piston core (NP-U1383E16,28) retrieved from the North Pond of the Mid-Atlantic Ridge, and two piston cores from the North Atlantic

Gyre17) (Supplementary Data 1), we found that the NOB across these cores are far outnumbered by AOA beyond the upper theoretical limit at many investigated depths (Fig. S1). When combining

observations from all 11 sediment cores (a total of 82 unique samples) (Fig. 1C), we observed that the abundances of AOA and NOB showed a linear relationship again, but with a slope of 26:1.

The AOA:NOB abundance ratio is higher than the upper boundary (15.8) of the theoretical range in 56 of 82 samples (median = 43.3, with the 99% confidence interval [16.6, 83.9]; Fig. 1E).

The apparent excess of AOA over NOB in these cores indicates that (i) some AOA are inactive or do not contribute to nitrite production, or more likely, (ii) there are yet unidentified NOBs

present. A BACTERIAL PHYLUM _CANDIDATUS_ NITROSEDIMINICOLOTA DEFINED BY MAGS FROM MARINE SEDIMENTS To elucidate which microbes are likely overlooked NOBs in marine sediments, we focused on

the metagenome sequencing data generated for two investigated sediment locations: four sediment horizons of AMOR core GS14-GC08, four horizons of NP-U1383E of North Pond38. Through genome

binning and refinement, we noticed three MAGs (Bin_086, Bin_096, and Bin_108) containing genes encoding the nitrite-oxidizing enzyme nitrite oxidoreductase (Nxr) but not affiliated with any

well-defined bacterial phylum. All three MAGs are of high completeness ( > 92%; Table 1) and low fragmentation ( < 73 scaffolds; Table 1) and therefore should be regarded as

high-quality genomes. The genome sizes are in the range of 1.8–2.4 Mbp. Automatic classification based on the 120 bacterial single-copy genes suggests that they are affiliated with an

understudied bacteria phylum (with the placeholder JADFOP01 in the GTDB RS214 Release), which previously included three MAGs (B6D1T2, B58T1B8, and B13D1T1) recovered from hadal sediments

beneath the Mariana Trench42. The novel phylogenetic affiliation of the now total six MAGs included in the JADFOP01 phylum is confirmed by phylogenetic analyses. Within the phylogenetic

trees based on the concatenated 120 bacterial single-copy genes (Fig. 2B) and 14 conservative single-copy ribosomal proteins (Fig. S2), the six MAGs form a branch separated from several

established bacterial phyla such as Nitrospinota (containing NOB), Tectomicrobia, Nitrospinota_B, Schekmanbacteria, and UBA8248 (Fig. 2A). The average nucleotide identities (ANIs) between

members of JADFOP01 and those in the established phyla are in the range of 47–53%, much lower than the threshold of 83% distinguishing bacterial phyla43 and supporting the view that these

MAGs represent a distinct bacterial phylum. The novel phylogenetic affiliations of these MAGs are confirmed by phylogenetic analysis based on the 16 S rRNA gene, which shows a congruent

topology with that based on both 120 single-copy genes and ribosomal proteins (Fig. 2B). We tentatively name this phylum _Candidatus_ Nitrosediminicolota, for their prevalence in globally

distributed marine sediments (see Etymology description). The calculated average amino acid identities (AAIs) among the six MAGs are >80% (Fig. S3), placing them in the range suggested

for genomes belonging to the same genus [65–95%43]. We tentatively name this genus _Candidatus_ Nitrosediminicola. Within this genus, three MAGs (Bin_096, B6D1T2, and B13D1T1) show AAIs

higher than 95% and should fall into the same species, for which we suggest a provisional name _Candidatus_ Nitrosediminicola aerophilus. Bin_086 and Bin_108 also shared an AAI higher than

95% and belong to the same species, which we provisionally name _Candidatus_ Nitrosediminicola anaerotolerans. The remaining MAG B58T1B8 shows AAIs <79% with all other _Ca_.

Nitrosediminicola MAGs and therefore should represent a third species that we do not name as it is not found in our samples. Therefore, the six MAGs of _Ca_. Nitrosediminicola reported here

should be resolved to three species within a single genus. _CA_. NITROSEDIMINICOLOTA IS PREVALENT IN OLIGOTROPHIC MARINE SEDIMENTS To explore the global occurrence of _Ca_.

Nitrosediminicolota, we searched public amplicon sequencing datasets in the IMNGS database44 for the 16 S rRNA gene sequences of our high-quality MAGs (See Materials and Methods for

details). _Ca_. Nitrosediminicolota is present with > 0.1% relative abundances in 300 globally-distributed samples (Supplementary Data 2), which are mapped in Fig. 2C. Except for two soil

and 13 basaltic rock samples (from the Dorado outcrop45 and North Pond46), the vast majority of the _Ca_. Nitrosediminicolota-containing samples are marine sediments (Fig. 2D). All of the

marine sites are oligotrophic sediments beneath the oligotrophic gyres of the Pacific47, Atlantic17, and Indian Oceans48, mid-ocean ridges19,38,39, hadal trenches40,49, and the Gulf of

Mexico50 (Fig. 2C). The distribution of the _Ca_. Nitrosediminicolota phylum suggests it harbors microbes specialized for oligotrophic marine sediments. _CA_. NITROSEDIMINICOLOTA BACTERIA

CONTAIN ALL KEY GENES OF NITRITE OXIDIZERS _Ca_. Nitrosediminicolota members contain nitrite oxidoreductase (NXR), the key enzyme for nitrite oxidation in microorganisms. NXR is present in

four _Ca_. Nitrosediminicola MAGs (Bin_086, Bin_108, B6D1T2, and B58T1B8) that span all three species in this genus (Fig. 3A). Considering the high similarities ( > 95% AAI) among the

three MAGs represented by B6D1T2, it is likely that the absence of NXR in the other MAGs (Bin_096 and B13D1T1) of this species is due to their lower genome completeness (Table 1). The NXR

operons in all NXR-containing _Ca_. Nitrosediminicolota genomes except B58T1B8 are present in the middle of scaffolds with lengths between 31 and 139 kbp (Fig. S4). Also, the gene

arrangements around NXR in these _Ca_. Nitrosediminicolota genomes reconstructed from different geographic locations are generally consistent, suggesting that the NXRs are unlikely to be

erroneously binned from other microbes. The structure of the putative NXR operons within _Ca_. Nitrosediminicolota genomes, consisting of NxrABC and a chaperone subunit annotated as NxrD

(Fig. S4), is similar to those observed in Chloroflexota (_Ca_. Nitrocaldera robusta and _Ca_. Nitrotheta patiens11) and _Nitrotoga_ NOB. Upstream of the NXR operon in the _Ca_.

Nitrosediminicolota genomes are genes encoding thiosulfate reductase and arsenite oxidase (Fig. S4). Like known NXR, these two enzymes are molybdenum-containing oxidoreductases. The genes

downstream of the NXRs encode cysteine desulfurase (iscS), a Fe-S cluster assembly scaffold protein (iscU), and Fe-S cluster assembly chaperones (hscAB), which are involved in the formation

of Fe-S clusters51, a critical part of many molybdenum-containing oxidoreductases including NXR. The putative NXR may enable members of _Ca_. Nitrosediminicola to generate energy from

nitrite-nitrate interconversion. Aerobic NOBs need oxygen as their terminal electron acceptor. Five of the six _Ca_. Nitrosediminicola genomes contain a cytochrome _c_ oxidase (CoxABCDE)

(i.e., heme-copper oxygen (HCO) reductase) (Fig. 3A), a critical enzyme involved in oxygen respiration, while its absence in the sixth (B13D1T1) could be due to the lower genome completion

level. Phylogenetic analysis of cytochrome _c_ oxidase indicates that the sequences of _Ca_. Nitrosediminicola form a clade separated from other bacterial phyla and fall within the broad

branch of the A1 Clade of heme-copper oxygen reductase (Fig. 3C). _Ca_. Nitrosediminicola members lack the cytochrome _bd_-type oxidases that are common in _Nitrospinaceae_5,52 and

_Nitrospiraceae_53 or _cbb3_-type cytochrome _c_ oxidase. The cytochrome _c_ oxidase can receive electrons from NXR for aerobic respiration, and the protons released by this process can help

to maintain the proton gradient that drives the ATP synthesis in Complex V. The presence of oxygen-respiring cytochrome _c_ oxidase likely also enables them to complete the

electron-transport chain and support the high abundances of _Ca_. Nitrosediminicola in oxic sediments. Characterized NOBs have been suggested to acquire the NXR module in different

evolutionary pathways and the horizontal transfer of NXR is likely a major driver for the spread of the capability to gain energy from nitrite oxidation during bacterial

evolution9,11,52,54,55. In particular, the canonical marine aerobic NOBs affiliated to the genera _Nitrospira_ and _Nitrospina_ are suggested to obtain their NXR from anammox bacteria in the

Brocadiales order within the Planctomycetota phylum41. Considering the distinct phylogenetic affiliations between the newly found _Ca_. Nitrosediminicola and the canonical NOB, we checked

whether they acquired the nitrite oxidation capacity through the same evolutionary path. As with the NXR gene subunit organization (nxrABCD), the specific amino acid sequences of the NXR

alpha subunit (NxrA) suggested that the four NXR-bearing _Ca_. Nitrosediminicola members are more similar to the recently characterized NOB of _Nitrotoga_55,56,57 and Chloroflexota (_Ca_.

Nitrocaldera robusta and _Ca_. Nitrotheca patiens11) than _Nitrospira_ and _Nitrospina_ (Fig. 3B). _Ca_. Nitrosediminicolota members thus may have acquired NXR from a donor similar to

Chloroflexota and _Nitrotoga_ NOB rather than that of taxa within the _Nitrospiraceae_/_Nitrospinaceae_/Anammox clade. All but one (Bin_096) of the _Ca_. Nitrosediminicola genomes encode a

copper-containing nitrite reductase (NirK) (Fig. 3A), which can reduce nitrite to nitric oxide and is present in some NOBs6,54,58. On the maximum-likelihood phylogenetic tree of bacterial

NirK _Ca_. Nitrosediminicola genomes form an independent cluster (Fig. S5). The close relatives of _Ca_. Nitrosediminicola NirK are all from ultra-small-celled archaea affiliated with _Ca_.

Woesearchaeota, rather than Nitrospinota, Nitrospinota_B, Tectomicrobia, UBA8284, or Schekmanbacteria, indicating that NirK in _Ca_. Nitrosediminicola may have a different origin than the

majority of the _Ca_. Nitrosediminicola genes. For the full respiratory electron-transport chain, _Ca_. Nitrosediminicola genomes have Complex I, Complex II, Alternative Complex III, Complex

IV (described above), and Complex V (F-type ATPase) (Fig. 3A), like other previously characterized aerobic NOB. This complete oxygen respiratory electron-transport chain likely enables them

to oxidize nitrite under oxic conditions. Regarding the central carbon metabolism, similar to the two newly-cultured NOBs affiliated with _Nitrospinaceae_ from coastal sediments5, _Ca_.

Nitrosediminicola species encode most key genes of the reductive tricarboxylic acid (rTCA) cycle (Figs. 3 and 4), including the hallmark enzymes 2-oxoglutarate:ferredoxin oxidoreductase and

pyruvate:ferredoxin oxidoreductase. Similar to nitrite-oxidizing Chloroflexota11, the ATP-citrate lyase is absent, whose function could be replaced by the reversibility of the encoded

citrate synthase59,60. The rTCA cycle may enable _Ca_. Nitrosediminicola bacteria to fix CO2 as proposed previously for _Nitrospira_ and _Nitrospina_52,54,61. The electrons for carbon

fixation may be derived from nitrite oxidation52. The _Ca_. Nitrosediminicola genomes also encode the gluconeogenesis and the pentose phosphate pathways (Fig. 4), which may be employed for

the synthesis of precursor metabolites in these NOBs, as previously proposed for _Nitrospira moscoviensis_61. Another feature of _Ca_. Nitrosediminicola is that five of its six member

genomes contain a urease operon (Fig. 3A and Fig. S6) (See Supplementary Note 1), which may enable them to access this pool for substrates and engage in reciprocal feeding with co-occurring

ammonia-oxidizing archaea16,25 to increase their metabolic fitness in marine sediments. The ABC transporters of iron(III), zinc, phospholipids lipoprotein, and heme are conserved in _Ca_.

Nitrosediminicolota genomes (Fig. 3A). Like many sediment bacteria, they lack genes for flagellar assembly and chemotaxis. _Ca_. Nitrosediminicolota members more likely employ the putative

NXR to perform nitrite oxidation rather than heterotrophic denitrification, due to the following reasons. First, they mainly inhabit oligotrophic deep-sea sediments (Fig. 2C), which

typically contain limited organic matter and deep oxygen penetration, and what organic matter that is available is largely inaccessible to heterotrophs through protection by mineral

adsorption62. Second, their genomes contain no genes involved in the transport of oligosaccharides, monosaccharides, or amino acids, and only one genome (Bin_108) contains formate

dehydrogenase, indicating that their capacity for organic matter respiration is minimal. Because the absence of sulfide and methane in the investigated AMOR sediments63, they are also

unlikely to be capable of autotrophic denitrification. While all members of _Ca_. Nitrosediminicolota reported here appear to retain nitrite oxidation capacity, conclusively including all

_Ca_. Nitrosediminicolota among NOB requires cultures to prove biogeochemical function, especially under anoxic conditions. _CA_. NITROSEDIMINICOLOTA RESOLVES THE NITRIFIER ABUNDANCE

DISCREPANCY Given the likely nitrite oxidation capacity of the newly defined _Ca_. Nitrosediminicolota, we re-calculated the abundances of combined NOB (defined as the sum of

_Nitrospiraceae_, _Nitrospinaceae_, and _Ca_. Nitrosediminicolota) in the sediment cores by including these as part of the NOB community (Supplementary Data 1). In the five Atacama Trench

sediment cores, the abundances of AOA vs. NOB in the oxic zones did not significantly change and still fell into the theoretical range of 2.6–15.8, with a mean AOA:NOB abundance ratio of 7.3

(Fig. 1B). For the 11 cores from the Arctic and Atlantic Ridges, however, the updated abundance ratios of AOA and NOB fell closer to the theoretical range (Fig. 1D), with a mean AOA:NOB

abundance ratio of 9.6. The median of AOA:NOB ratio of these 82 oxic samples decreased dramatically from 43.3 to 5.6, with a 99% confidence interval of 3.9–8.4 (Fig. 1E). These results align

with the theoretical prediction based on the observed growth features of marine AOA and NOB. Admittedly, microbes in deep-sea sediments face extreme energy limitation and are generally

sustained by basal power requirements64. Therefore, higher bulk reaction rates are typically accompanied by higher microbial abundances across samples of different depths/ages, because the

underlying microbes have similar power requirements [e.g., AOA28 and sulfate-reducing bacteria65]. Although other factors such as transcription may also influence the relative abundance of

AOA and NOB, our quantitative data indicate that counting these novel bacteria as NOBs helps resolve the apparent abundance mismatch between AOA and NOB in marine sediments. To check whether

_Ca_. Nitrosediminicolota is the dominant nitrite oxidizer in both oxic and anoxic marine sediments, we compared the abundances of _Ca_. Nitrosediminicolota to those of canonical NOB

affiliated with the families _Nitrospinaceae_ and _Nitrospiraceae_ in AMOR sediment cores. Although these two NOB families, especially _Nitrospinaceae_, are also abundant in oxygen-deficient

waters35, in AMOR sediments they are generally confined within the oxic zones with <4% relative abundances among the total prokaryotic communities (Figs. 5A, 5B, and Fig. S7B). In

contrast, _Ca_. Nitrosediminicolota is present in most of the investigated depths and is particularly abundant in the deep anoxic layers. Restricting analysis to the oxic zone (Fig. 5A)

where the organisms co-occur, _Ca_. Nitrosediminicolota dominates over _Nitrospinaceae_ and _Nitrospiraceae_ in all but a few depths (Fig. 5D and Fig. S7D). The depth-averaged relative

abundance of _Ca_. Nitrosediminicolota in the putative NOB communities in oxic sediments of the 11 cores is 50–80%, while _Nitrospiraceae_ and _Nitrospinaceae_ each only account for 8–25%

(Fig. 1F). Thus, _Ca_. Nitrosediminicolota is roughly 2–4 times more abundant than the canonical NOBs in oxic marine sediments. The dominance of _Ca_. Nitrosediminicolota is also evident in

the calculated absolute abundance profiles in the four AMOR cores (Fig. 5C and Fig. S7C), who exhibit 2–4 orders of magnitude higher absolute abundances than _Nitrospinaceae_ and

_Nitrospiraceae_ in the basal part of the oxic zones. Being far more abundant than canonical NOBs, _Ca_. Nitrosediminicolota can potentially contribute significantly to nitrite oxidation in

global oligotrophic marine oxic sediments. REDOX NICHES DISTINGUISH _CA_. NITROSEDIMINICOLA SPECIES To reveal which _Ca_. Nitrosediminicolota species are present and can thrive in the anoxic

sediment layers of the AMOR cores, we interrogated the distribution of individual species represented by the _Ca_. Nitrosediminicola MAGs in the four AMOR cores previously reported38. Based

on the comparison of 16 S rRNA gene sequences between _Ca_. Nitrosediminicola MAGs and the amplicon sequencing OTUs (See Materials and Methods), _Ca_. Nitrosediminicola Bin_086 and _Ca_.

Nitrosediminicola Bin_096 reported here correspond to OTU_4 and OTU_235 reported in Zhao et al.38, respectively. It is worth noting that these two OTUs could be classified as members of the

Schekmanbacteria phylum (SILVA 138.1) or the Nitrospinota phylum (MD2896-B214 class, SILVA 128), depending on the reference databases used in the classification. The matches between the MAGs

reported here and the previously reported OTUs set the basis for tracking the vertical distribution of the two _Ca_. Nitrosediminicola species in the four AMOR cores. We observed distinct

redox niche preferences of the two _Ca_. Nitrosediminicola species derived from the AMOR cores. While _Ca_. Nitrosediminicolota Bin_096 (OTU_235) is exclusively detected in the oxic zones of

the four AMOR cores, _Ca_. Nitrosediminicolota Bin_086 (OTU_4) was detected in all investigated sediment layers and is particularly abundant in anoxic layers (Fig. 5E and Fig. S7E).

Therefore, _Ca_. Nitrosediminicolota Bin_096 appears to be an oxic niche specialist, while _Ca_. Nitrosediminicolota Bin_086 may be an anoxia-tolerant generalist. The high relative abundance

of _Ca_. Nitrosediminicolota in the deep anoxic layers of the AMOR cores (Fig. 5B and Fig. S7B) is due to the prevalence of _Ca_. Nitrosediminicola Bin_086 in the anoxic sediments. The

maximum relative abundance of _Ca_. Nitrosediminicola Bin_086 (31% of the total community) was detected at 250 cm below the seafloor of GS14-GC08 (Fig. 5B). Whether _Ca_. Nitrosediminicola

Bin_086 can perform nitrite oxidation in the deep anoxic sediment layers requires future study. Such a redox niche preference difference between different lineages of the same functional

guild is not novel, and has been previously observed for anammox bacterial families in AMOR sediments19. To reflect their preferred redox niches, we propose to name Bin_096 _Ca_.

Nitrosediminicola aerophilus (prefer aerobic conditions), and Bin_086 _Ca_. Nitrosediminicola anaerotolerans (tolerant to anaerobic conditions). The abundant _Ca_. N. anaerotolerans may

compete with anammox in anoxic layers. In GS14-GC08, the relative and absolute abundances of _Ca_. N. anaerotolerans exhibited two peaks in the anoxic sediments (Fig. 5E, F), which are

located above and below the nitrate-depletion zone. Interestingly, the peak (of both the relative and absolute abundances) of anammox bacteria was observed between the two _Ca_. N.

anaerotolerans abundance maxima, which appears to indicate potential competition between these two nitrite-consuming groups. Although the two abundance peaks of _Ca_. N. anaerotolerans are

not resolved in the other AMOR cores (GS14-GC09, GS16-GC04, and GS16-GC05) due to their short core length or low depth resolution, they generally show that the abundance of _Ca_. N.

anaerotolerans decreases along with the increase of anammox bacteria abundance in anoxic sediments (Fig. S7) (Supplementary Data 3). Although _Ca_. N. anaerotolerans is likely involved

nitrite oxidation in the upper oxic sediments, it remains unclear whether they can maintain the same capacity or need nitrite for other purposes in layers without detectable oxygen.

Therefore, whether _Ca_. N. anaerotolerans competes for nitrite with anammox bacteria is still unclear. Nevertheless, our observation suggests that anammox bacteria retain better fitness

over _Ca_. N. anaerotolerans in anoxic sediments where nitrate and nitrite supply may be limiting. To identify what mechanisms may drive the distinct redox niche preferences between the two

prevailing Nitrosediminicolota species, we performed a comparative genomic analysis based on four MAGs (_Ca_. N. anaerotolerans represented by Bin_086 and Bin_108, and _Ca_. N. aerophilus

represented by Bin_096 and B6D1T2). A total of 5928 genes of the four MAGs form 1355 gene clusters. There are 34 (2.5% of the total) gene clusters uniquely present in _Ca_. N. anaerotolerans

and 37 (2.7%) in _Ca_. N. aerophilus, while 989 (73.0%) gene clusters are shared among the four Nitrosediminicolota genomes (Supplementary Data 4). Thiosulfate reductase is among the

enzymes encoded by the gene clusters uniquely present in _Ca_. N. anaerotolerans. Thiosulfate is a common sulfur cycle intermediate at low concentrations in marine sediments and is mainly

produced by the oxidation of hydrogen sulfide derived from sulfate reduction66,67. The presence of thiosulfate reductase in _Ca_. N. anaerotolerans may equip it with the capacity to use

thiosulfate as an electron acceptor in anoxic sediments. In addition, unlike _Ca_. N. aerophilus, _Ca_. N. anaerotolerans also contains genes involved in cobalamin (Vitamin B12) synthesis.

Unique gene clusters in the _Ca_. N. aerophilus genomes encode ABC-type proline/glycine betaine transporters for bacterial osmoregulation and Mu-like prophage proteins involved in bacterial

antiviral defense68 (Supplementary Data 4). Other gene clusters found to be uniquely present in only one Nitrosediminicolota species have no known roles in energy metabolism. CONCLUSION Our

compilation of AOA and canonical NOB abundances in global oxic marine sediments argues that there were overlooked yet abundant NOB. Through genome reconstruction and phylogenetic analyses,

we discovered a bacterial phylum, _Ca_. Nitrosediminicolota, which currently contains six genomes that can be resolved to three species in the same genus _Ca_. Nitrosediminicola. Metabolic

potential analyses of _Ca_. Nitrosediminicolota genomes indicated that they contain the genetic machinery for nitrite oxidation as well as other versatile metabolisms such as urea

utilization. _Ca_. Nitrosediminicolota is widespread in oligotrophic marine sediments. They are more abundant in the oxic zones of AMOR sediments by a factor of 2–4 compared to the canonical

NOBs affiliated with _Nitrospiraceae_ and _Nitrospinaceae_. Counting them as NOB resolves the abundance mismatch between AOA and NOB in broad oxic marine sediments and permits closing the

nitrogen cycle in oxic marine sediments without invoking denitrification. Although being affiliated with the same genus, the two dominant _Ca_. Nitrosediminicola species in the AMOR

sediments manifest distinct redox niche preferences: _Ca_. N. aerophilus is only present in the oxic zone whereas _Ca_. N. anaerotolerans exist both in the oxic and anoxic zones. Its

capacity for thiosulfate reduction may allow _Ca_. N. anaerotolerans to thrive under anaerobic conditions but cultivation efforts are needed to confirm these genome-based metabolic

inferences. Considering their global occurrence and high abundance in sediments not only on the Arctic ridge but also beneath open ocean gyres and in hadal trenches, _Ca_.

Nitrosediminicolota may play a critical role in sediment nitrogen cycling across the entire oligotrophic marine expanse. ETYMOLOGY DESCRIPTION _Candidatus_ Nitrosediminicolota

(Ni.tro.se.di.mi.ni.co.lo’ta. N.L. masc. n. Nitrosediminicola, a bacterial genus; -ota, ending to denote a phylum; N.L. neut. pl. n. Nitrosediminicolota, the Nitrosediminicola phylum).

_Candidatus_ Nitrosediminicola (Ni.tro.se.di.mi.ni’co.la. Gr. neut. n. nitron, mineral alkali; L. neut. n. sedimen, sediment; L. masc./fem. n. suff. -cola, inhabitant, dweller; N.L. masc. n.

Nitrosediminicola, a nitrate forming sediment-dweller). _Candidatus_ Nitrosediminicola aerophilus (aero, oxygen; suff. -philus, lovers; aerophilus, an oxygen lover, highlighting the

preference of this microbe to the oxic zone of marine sediments). Phylogenetically affiliated with the genus _Ca_. Nitrosediminicola, phylum _Ca_. Nitrosediminicolota. This species currently

contains three genomes from marine sediments (two from the Mariana Trench and one from the Arctic Mid-Ocean Ridge). The arctic genome consists of 73 scaffolds of 1,837,265 bp. The DNA G + C

content is 60.6%. It is preferably present in the oxic sediment layers. It contains metabolic functions of aerobic nitrite oxidation and urea hydrolysis. _Candidatus_ Nitrosediminicola

anaerotolerans (anaero, lack of oxygen; suff. -tolerans, being tolerant to something; anaerotolerans, being tolerant to anaerobic conditions, highlighting the tolerance of this microbe to

the anoxic zone of sediment columns) Phylogenetically affiliated with the genus _Ca_. Nitrosediminicola, phylum _Ca_. Nitrosediminicolota. This species contains two strains recovered from

two Arctic sediment cores. Their genomes consist of 48–61 scaffolds, with total genome sizes of 2.2–2.5 Mbp. The DNA G + C content is 62.3%. The genomes are present in both the oxic and

anoxic sediment layers. It contains metabolic functions of nitrite-nitrate conversion, urea hydrolysis, and thiosulfate reduction. METHODS SAMPLING COLLECTION AND CHARACTERIZATION This study

uses samples and data of sediment cores from the Arctic, Atlantic, and Pacific Oceans. The procedures of sample collection, processing, and data generation were thoroughly described in

refs. 16,17,38,39. Briefly, sediment cores were retrieved by gravity coring from the seabed of various sites on the ridge flanks of the Arctic Mid-Ocean Ridge beneath the Norwegian-Greenland

Sea38,39 or by piston coring from the North Atlantic Ocean16,17. Upon core retrieval, the thickness of the oxic zone of each core was determined by measuring the in-situ oxygen

concentrations using a needle-type fiber-optic oxygen microsensor (PreSens), except for GS13-CC2 in which the oxygen penetration depth was not measured but inferred as the depth marking the

appearance of dissolved Mn in the porewater41. For the Arctic cores where the distribution patterns of _Ca_. Nitrosediminicola species were investigated in this study, the subsampling of

microbiology samples (using sterile 10 mL cutoff syringes) and porewater extraction were performed immediately on the sampling half using Rhizons samplers after the split. A QuAAtro 114

continuous flow analyzer (SEAL Analytical Ltd) was used to colorimetrically measure nitrate, nitrite, and ammonium concentrations in the porewater. EXPLORING AOA AND NOB ABUNDANCES IN MARINE

OXIC SEDIMENTS Similar to Zhao et al.28 where AOA’s distribution was explored, we investigated the distribution of NOB in oxic marine sediments based on the existing 16 S rRNA gene amplicon

sequencing data for 11 sediment cores with thick oxic zones. In addition to the cores considered in Zhao et al.28, we also included four additional AMOR cores (GS13-CC2, GS14-GC02,

GS14-GC04, and GS15-GC01 reported in refs. 39,41) and two piston cores from the North Atlantic Gyre17. The amplicon sequencing data of the total eight AMOR cores and the North Pond core were

generated using the same procedure. Briefly, the total DNA in the sediment samples was extracted using the PowerLyze DNA extraction kits (MOBIO Laboratories, Inc.). Amplicon of the 16 S

rRNA gene was prepared using the two-round PCR amplification strategy with the “universal” primers of Uni519F/806r, as described in Zhao et al.38. The amplicon libraries were sequenced on an

Ion Torrent Personal Genome Machine. The raw sequencing reads were quality filtered and trimmed to 220 bp using the USEARCH v11.0.667 pipeline69. The taxonomic classification of OTUs was

performed using the lowest common ancestor algorithm implemented in the Python version of CREST4 (the latest version of CREST70) against the SILVA 138.1 Release71. The total cell numbers

were taken as the sum of the archaeal and bacterial 16 S rRNA genes as determined by qPCR. For the remaining two cores from the North Atlantic Gyre17, we downloaded the amplicon sequencing

data from the NCBI database and employed the same data analysis pipeline to run the reads trimming, OTU clustering and classification. We initially considered the abundance of canonical NOB

affiliated with the families _Nitrospiraceae_ and _Nitrospinaceae_. For both AOA and canonical NOB, the absolute abundance of a functional group was calculated as the product of the total

cell numbers (the sum of archaeal and bacterial 16 S rRNA gene abundances) and its relative abundances in the total communities (as assessed by 16 S rRNA gene amplicon sequencing), as

previously employed for investigation of anammox bacteria38,72. We then also considered members of _Ca_. Nitrosediminicolota as some overlooked NOB in marine sediments and calculated the

total NOB abundance by taking NOB abundance as the sum of _Nitrospiraceae_, _Nitrospinaceae_, and _Ca_. Nitrosediminicolota. We also investigated the community structure of NOB based on the

16 S rRNA gene amplicon sequencing data. Through the phylogenetic analysis of 16 S rRNA gene sequences (see the description below), we confirmed that 10 OTUs were affiliated to the

_Nitrospiraceae_ family, 14 OTUs _Nitrospinaceae_, and 8 OTUs originally classified as members of the Schekmanbacteria phylum should correspond to the _Ca_. Nitrosediminicolota phylum. Note

that among the 8 putative _Ca_. Nitrosediminicolota OTUs, only three were verified to be members of _Ca_. Nitrosediminicolota by the phylogenetic analysis of the 16 S rRNA gene (Fig. 2B) and

therefore were included in the abundance calculations of _Ca_. Nitrosediminicolota, while the remaining five minor OTUs were affiliated with other bacterial phyla. For each of these three

groups, the relative abundance was taken as the sum of the relative abundances of the corresponding OTUs. To quantitatively evaluate the dominance of these three putative NOB lineages based

on the observed depth profiles from arbitrarily selected sediment depths, we calculated the depth-averaged relative abundance for each of the three lineages using trapezoidal integration, as

implemented in the R package _pracma_ (https://github.com/cran/pracma). GENOME BINNING AND REFINEMENT For metagenome-assembled genome recovery, we focused on the metagenome sequencing data

of core GC08 and NP-1383E, which were generated and reported by ref. 38. The procedures for DNA extraction, library preparation, metagenome sequencing, raw data quality control, assembly,

and genome binning were described therein. Briefly, DNA was extracted from ~7 g of sediment from each selected depth. Metagenomic libraries were sequenced (2 × 150 bp paired-end reads) by an

Illumina HiSeq 2500 sequencer. The quality of the raw sequencing data was first checked using FastQc v0.11.973, with the adapters removed and reads trimmed using Trimmomatic v0.3974 based

on the quality scores. The quality-controlled paired-end reads were de novo assembled into contigs using MEGAHIT v1.1.275 with the _k_-mer length varying from 27 to 117. Contigs larger than

1000 bp were automatically grouped into genome bins using MaxBin2 v2.2.576 and MetaBAT v2.15.377 with the default settings, and the best representatives were selected using DAS_Tool v1.1678.

The quality of the obtained bins was assessed using CheckM2 v1.0.279. In this study, three putative NXR-containing MAGs (Bin_086, Bin_096, and Bin_108) were found to be affiliated with

unknown bacterial phyla and were thus subject to further analyses. To ensure the binning correctness and also improve the MAG quality, quality-trimmed reads of the sample showing the highest

genome coverage were mapped onto the contigs using BBmap80, and the successfully aligned reads were re-assembled using SPAdes v3.12.081 with the _k_-mers of 21, 33, 55, and 77. After the

removal of contigs shorter than 1000 bp, the resulting scaffolds were visualized and manually re-binned using gbtools v2.6.082 based on the GC content, taxonomic assignments, and

differential coverages of contigs across multiple samples, with the input data generated using the following steps. Coverages of contigs in each sample were determined by mapping trimmed

reads onto the contigs using BBMap v.37.6180. The taxonomic classification of contigs was assigned by BLASTn83 according to the taxonomy of the single-copy marker genes in contigs. SSU rRNA

sequences in contigs were identified using Barrnap84 and classified using VSEARCH85. The mapping, re-assembly, and re-binning process was repeated 5–7 times until the quality of the genomes

could not be improved further. The refined MAGs were classified using GTDB-tk v2.3.086 with the default setting. The MAG quality was checked again using CheckM2 v1.0.279. GENOME ANNOTATION

Genomes discussed in this study were annotated together with their close relative MAGs [i.e., three MAGs recovered from Mariana Trench sediments42] and also representative MAGs in the phyla

Nitrospinota and Nitrospinota_B in the GTDB 08-RS214 Release (https://gtdb.ecogenomic.org/). Genes in these genomes were predicted using Prodigal87. Genome annotation was conducted using

Prokka v1.1388, eggNOG89, and BlastKoala90 using the KEGG database. The functional assignments of genes of interest were also confirmed using BLASTp84 against the NCBI RefSeq database. The

metabolic pathways were reconstructed using KEGG Mapper91. The gene organizations around NXR in _Ca_. Nitrosediminicolota and also other selected NOBs in the Nitrospirota, Nitrospinota, and

Chloroflexota phyla were visualized using GeneSpy v1.292, with the gff files from the Prokka annotation as the input. LINKING MAGS WITH AMPLICON SEQUENCING OTUS To track the vertical

distribution pattern of the two _Ca_. Nitrosediminicola species in the four AMOR cores, we searched the corresponding OTUs of the two genomes by comparing their 16 S rRNA gene sequences

(i.e., the query sequences) with the amplicon sequencing OTUs (the subject sequences) with BLASTp93. Because Bin_096 reconstructed from AMOR sediments lacked a 16 S rRNA gene sequence, we

used that of B6D1T2 (another strain highly similar to Bin_096) to run the comparison. _Ca_. Nitrosediminicola Bin_086 has a full-length (1,565 bp) 16 S rRNA gene sequence, which is a 100%

match with OTU_4. _Ca_. Nitrosediminicola Bin_096 corresponds to OTU_235, given the 99.6% match of the 16 S rRNA gene between them. COMPARATIVE GENOMIC ANALYSIS We performed a comparative

analysis on the three representative genomes of the two _Ca_. Nitrosediminicola species using Anvi’o v7.194 according to the pangenome analysis workflow. All genomes were first annotated

using Prokka v.1.1488 and BLASTp using the Clusters of Orthologous Groups of Proteins (COG)95 as the reference database. The comparative genomic analysis uses BLAST to quantify the

similarity between each pair of genes, and the Markov Cluster algorithm (MCL)96 (with an inflation parameter of 2) to resolve clusters of homologous genes. The shared and unique genes in the

two genomes were identified via the functional enrichment analysis97. Average amino acid identities between genomes were calculated using EzAAI v.1.2.298 with the default setting.

PHYLOGENETIC ANALYSES To pinpoint the phylogenetic placement of the newly recovered MAGs and their relative genomes, we performed phylogenetic analyses for them together with high-quality

genomes that were included in the GTDB Release 08-RS214. The 120 single-copy genes were identified, aligned, and concatenated using GTDB-tk v2.3.086 with the “classify_wf” command. The

maximum-likelihood phylogenetic tree was inferred based on this alignment using IQ-TREE v1.5.599 with LG + F + R7 the best-fit model selected by ModelFinder100, and 1000 ultrafast bootstrap

iterations using UFBoot2101. To provide support to this phylogenomic analysis, we also performed the phylogenomic analysis based on the 14 syntenic ribosomal proteins (rpL2, 3, 4, 5, 6, 14,

16, 18, 22, and rpS3, 8, 10, 17, 19). These selected proteins were identified in Anvi’o v7.194 using Hidden Markov Model (HMM) profiles and aligned individually using MUSCLE102. Alignment

gaps were removed using trimAl103 in “automated” mode and the individual alignments of ribosomal proteins were concatenated. The maximum likelihood phylogenetic tree was reconstructed using

IQ-TREE v1.5.599 with LG + R7 as the best-fit model. A maximum-likelihood phylogenetic tree based on 16 S rRNA genes was also constructed for the above-mentioned genomes to confirm the

phylogenetic placement of the _Ca_. Nitrosediminicolota phylum. To expand this phylum on the tree beyond the available genomes, the putative _Ca_. Nitrosediminicolota OTUs from the amplicon

sequencing and their close relatives identified via BLASTn93 in the NCBI database were also included. Sequences were aligned using MAFFT-LINSi104 and the maximum-likelihood phylogenetic tree

was inferred as above, with 1000 ultrafast bootstraps. For the phylogenies of NxrA (nitrite oxidoreductase alpha subunit), the _Ca_. Nitrosediminicola sequences were used as the queries in

BLASTp93 searches in the NCBI database ( > 50% similarity and _E_-value of 10−6) to identify their close relatives. These sequences were aligned using MAFF-LINSi104 with reference

sequences from Koch et al.105 and complemented with known nitrite-oxidizing bacteria. For the phylogeny of UreC (urease alpha subunit), the sequences of _Ca_. Nitrosediminicola genomes were

used as the queries in the BLASTp93 search in the NCBI database (only hits of >50% similarity were retained), to identify their close relatives. These sequences were combined with

sequences from Zhao et al.41 and were aligned using MAFF-LINSi104. The same procedure was also used to prepare sequences for the phylogenetic analyses of NirK (copper-containing nitrite

reductase) and heme copper oxygen reductase. Phylogenetic trees for all proteins were generated as above. GLOBAL OCCURRENCE OF _CA_. NITROSEDIMINICOLOTA The global occurrence of _Ca_.

Nitrosediminicolota in natural environments was assessed using IMNGS44 against all public SRA datasets in the NCBI database with the 16 S rRNA gene sequences of high-quality _Ca_.

Nitrosediminicolota genomes as the query. Reads were counted as matching reads if they (i) were longer than 200 bp and (ii) showed >95% nucleotide sequence identity to the query. Samples

with less than 10 matching reads were discarded. Only natural environments with more than 0.1% relative abundances were retained for spatial mapping. The sample coordinates were mapped onto

a global map using the R packages _rgdal_ and _rgeos_. The basal global map was created in R using free vector and raster map data from Nature Earth (https://www.naturalearthdata.com/).

STATISTICS AND REPRODUCIBILITY Statistical analyses were performed in R v4.2.2106. The linear correlations between AOA and NOB abundances were calculated using the “_lm()_” function of R.

The abundance data used in this study were derived from single measurements of individual sediment samples without replicates from a total of 17 sediment cores (110 individual samples).

REPORTING SUMMARY Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article. DATA AVAILABILITY All sequencing data used in this

study are available in the NCBI Short Reads Archive under the project number PRJNA529480. The three _Ca_. Nitrosediminicolota genomes recovered in this study are available under the

accession number JAWJBM000000000 (_Ca_. N. anaerotolerans Bin_086), JAWJBN000000000 (_Ca_. N. anaerotolerans Bin_108), and JAWJBO000000000 (_Ca_. N. aerophilus Bin_096). Microbial abundance

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environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria (2014). Download references ACKNOWLEDGEMENTS Large-scale sediment coring opportunities from the

Arctic area were possible thanks to the efforts of chief scientist Rolf Birger Pedersen, the science parties, and the crew of R/V G.O. Sars. We thank Anita-Elin Fedøy for the help in

amplicon preparation, and Thomas Pollak, Sophie Abby, and Christa Schleper for their help in the metagenome sequencing data generation. We thank Aharon Oren for the microbial lineage naming

suggestions. This work was funded by Simons Foundation grant 622065 and National Science Foundation grants OCE-2138890 and OCE-2142998 to A.R.B. R.Z. was supported by the MIT Molina

Postdoctoral Fellowship. We are additionally grateful for the generosity of Dr. Bruce Heflinger in supporting the bablab, including this work. S.L.J. was supported by the Trond Mohn

Foundation and the University of Bergen through the Centre for Deep Sea Research (grant TMS2020TMT13). AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Earth, Atmospheric and

Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA Rui Zhao & Andrew R. Babbin * Centre for Deep-Sea Research, Department of Earth Science, University of

Bergen, Bergen, Norway Steffen L. Jørgensen Authors * Rui Zhao View author publications You can also search for this author inPubMed Google Scholar * Steffen L. Jørgensen View author

publications You can also search for this author inPubMed Google Scholar * Andrew R. Babbin View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS

R.Z. conceived this work. R.Z. and S.L.J. collected the Arctic sediment cores and obtained the geochemical, amplicon sequencing, and metagenome sequencing data. R.Z. compiled and analyzed

the relevant literature data included in Fig. 1. R.Z. and A.R.B. obtained and analyzed the genome data. R.Z. and A.R.B. wrote the manuscript with comments from all authors. CORRESPONDING

AUTHORS Correspondence to Rui Zhao or Andrew R. Babbin. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests. PEER REVIEW PEER REVIEW INFORMATION

_Communications Biology_ thanks Yiguo Hong, Barbara Bayer, and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editors: Linn

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CITE THIS ARTICLE Zhao, R., Jørgensen, S.L. & Babbin, A.R. An abundant bacterial phylum with nitrite-oxidizing potential in oligotrophic marine sediments. _Commun Biol_ 7, 449 (2024).

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