Vitamin B12conveys a protective advantage to phycosphere-associated bacteria at high temperatures

Abstract

AbstractMany marine microbes require vitamin B12(cobalamin) but are unable to synthesize it, necessitating reliance on other B12-producing microbes. Thus, phytoplankton and bacterioplankton community dynamics can partially depend on the production and release of a limiting resource by members of the same community. We tested the impact of temperature and B12availability on the growth of two bacterial taxa commonly associated with phytoplankton:Ruegeria pomeroyi, which produces B12and fulfills the B12requirements of some phytoplankton, andAlteromonas macleodii, which does not produce B12but also does not strictly require it for growth. For B12-producingR. pomeroyi, we further tested how temperature influences B12production and release. Access to B12significantly increased growth rates of both species at the highest temperatures tested (38ºC forR. pomeroyi, 40ºC forA. macleodii) andA. macleodiibiomass was significantly reduced when grown at high temperatures without B12, indicating that B12is protective at high temperatures. Moreover,R. pomeroyiproduced more B12at warmer temperatures but did not release detectable amounts of B12at any temperature tested. Results imply that increasing temperatures and more frequent marine heatwaves with climate change will influence microbial B12dynamics and could interrupt symbiotic resource sharing.