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

在这个项目中，研究人员将研究一组难以捉摸的基础化学自养伽马蛋白细菌的生理学，以及仅在细菌-动物宿主组合中发现的硫代营养途径。伽马蛋白细菌中的大量基础亚支是海洋生物地球化学重要的硫化物氧化自养生物；但很少有人培养，对它们的生态生理学知识仍然有限。其中一些细菌与海洋无脊椎动物在硫酸盐生境中共生，在那里它们为宿主解毒硫化物，在某些情况下，它们是宿主的唯一食物来源。大多数内共生菌在感染或被宿主动物吸收之前都有一个自由生活的阶段。但到目前为止，还没有一株硫代营养细菌共生体在培养中，对它们的生态生理和与宿主的生化相互作用知之甚少。这位研究人员最近在同一子分支中分离出了一株氧化硫化物的伽马蛋白细菌，其中包括许多具有自由生活阶段的内共生菌株，被称为硫代牛磺酸硫代变种。像许多适应低氧环境的内生共生菌一样，该菌株在低氧条件下或通过氧敏感酶Rubisco Form II的反硝化作用将碳固定到生物质中。该菌株在有机酸上表现出不同寻常的生长模式，其中之一是它似乎优先使用琥珀酸等有机酸作为固定二氧化碳的能源。T.thiomutagens可能是第一个在培养中仅与Rubisco形式II固定碳的专性自养细菌。初步试验表明，T.thiomutagens的生态生理学可能与硫代营养内共生菌非常相似。该项目将使研究人员能够通过培养实验、基因组学和蛋白质组学相结合的方式进一步阐明硫代变种的生理学。这种培养方法将导致对硫代变种的正式识别和描述。测序后的基因组将与已发表的内共生菌硫代营养菌基因组进行比较，以帮助确定硫代变种杆菌是否可以在未来的研究中作为内共生菌的替代品，并确定它是否也可能是伽马变形杆菌早期辐射的生态型代表。利用最近开发的质谱学技术，提出了两项蛋白质组学研究。第一项研究将阐明硫代牛磺酸的利用途径，第二项研究将阐明在摄取外源二氧化碳期间和之后生长在琥珀酸上的途径。扩大的参与目标包括在明尼苏达大学的学术生涯中一次指导五到六名其他退伍军人。这位调查者是霍华德·休斯医学院的一名研究导师，负责转学生物学方面的学生，并将在该项目期间继续指导本科生的研究。此外，研究人员将在奇卡诺人和美国原住民科学协会全国会议上组织一次关于共生的会议，主要由本科生参加。该项目得到美国国家科学基金会海洋科学博士后研究奖学金(OCE PRF)计划的支持，旨在支持早期职业科学家的创新研究，并增加美国海洋科学劳动力和研究社区的多样性。在海洋科学和可持续发展基金的支持下，该项目将使有前途的早期职业研究人员能够从事与海洋科学有关的独立研究事业，并扩大未被充分代表的群体在海洋科学领域的参与。

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.