_Proc. Natl Acad. Sci. USA_ doi:10.1073/pnas.0809533106 (2009) A pathogen that can cause gum disease in humans uses signals from another species to bolster its defences, find Matthew Ramsey

and Marvin Whiteley of the University of Texas in Austin. They report that hydrogen peroxide secreted by _Streptococcus_ bacteria stimulated _Aggregatibacter actinomycetemcomitans_ to make

more of a protein called ApiA, via a protein that acts as a sensor, OxyR. ApiA increases _A. actinomycetemcomitans_'s binding to a human protein called factor H, shielding this

bacterial species from attack by the human immune system. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Microbiology: Community assistance. _Nature_

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