OCE-PRF: Symbiosis unbound? Investigating the physiology, genome, and proteome of Thiotaurens thiomutagens, a novel marine sulfide-oxidizing bacterium

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In this project, the investigator will examine the physiology of an elusive group of basal chemoautotrophic Gammaproteobacteria and the thiotrophic pathway found exclusively in bacterial-animal host associations.A large number of basal sub-clades within the Gammaproteobacteria are marine biogeochemically-important sulfide-oxidizing autotrophs; but few have been cultivated and knowledge of their ecophysiologies remains limited. Some of these bacteria engage in symbiotic lifestyles with marine invertebrates in sulfidic habitats, where they detoxify sulfide for the host, and in some cases serve as the host's sole food source. Most of these endosymbionts have a free-living stage prior to infecting, or being taken up by the host animal. But to date, there is not a single strain of thiotrophic bacterial symbiont in cultivation and little is known about their ecophysiologies and biochemical interactions with their hosts. The investigator recently isolated a sulfide-oxidizing Gammaproteobacteria within the same sub-clade that includes many endosymbiotic strains with a free-living stage, dubbed Thiotaurens thiomutagens. Like many endosymbionts adapted to hypoxic regimes, this strain fixes carbon into biomass under low atmospheric oxygen or via denitrification using the oxygen-sensitive enzyme RuBisCO Form II. This strain exhibits unusual growth patterns on organic acids, one of which is that it appears to preferentially use an organic acid such as succinate, as an energy source to fix carbon dioxide. T. thiomutagens may be the first obligate autotrophic bacterium which fixes carbon solely with RuBisCO Form II in culture. Preliminary tests suggest that the ecophysiology of T. thiomutagens may be very similar to that of thiotrophic endosymbionts. This project will enable the investigator to further elucidate the physiology of T. thiomutagens through a combination of cultivation experiments, genomics, and proteomics. The cultivation approach will result in the formal recognition and description of T. thiomutagens. The sequenced genome will be compared with published genomes of endosymbiont thiotrophs to aid in the determination of whether T. thiomutagens may serve as a proxy for endosymbionts in future studies and determine whether it may also be an ecotype representative of the early radiation of the Gammaproteobacteria. Two proteomics studies are proposed using a recently developed mass spectrometry technique. The first study will elucidate the pathway for thiotaurine utilization and the second study will elucidate the pathways invoked during growth on succinate during and after the uptake of exogenous carbon dioxide. The broadening participation goals involve mentoring five to six other military veterans at a time through the course of their academic careers at the University of Minnesota. The investigator is a Howard Hughes Medical Institute research mentor to transfer students in biology and will continue to mentor undergraduates in research during this project. In addition, the investigator will organize a session on symbioses at the Society for Chicanos and Native Americans in Science National Conference, attended primarily by undergraduate students. This project is supported under the NSF Ocean Sciences Postdoctoral Research Fellowship (OCE PRF) program, with goals to support novel research by early career scientists and increase the diversity of the U.S. ocean sciences workforce and research community. With OCE-PRF support, this project will enable a promising early career researcher to establish themselves in an independent research career related to ocean sciences and broaden participation of under-represented groups in the ocean sciences.