Mixotrophic bacteria and the cryptic marine sulfur cycle: Mechanisms of carbon assimilation and sulfur oxidation in the Arctic96BD-19 GSO clade

知识价值：海洋提供了一个巨大的碳、氮、磷、硫和所有生命所需的其他元素的储存库。生活在海洋中的活跃而多样的微生物种群负责调节维持海水化学性质的营养转化。最近的一项研究发现了一种普遍存在的海洋细菌群，它们来自Arctic96BD-19 γ -变形菌硫氧化剂（GSO）谱系，与已知的硫氧化物种密切相关，后者在低氧水域中固定无机碳并氧化硫化物。gso在含氧水域中利用还原形式硫的潜力表明，它们是连接海洋碳和硫循环的关键物种。唯一已知的从Arctic96BD-19 gso谱系中分离出来的菌株现在已经在培养中，这使得关于它们在碳和硫循环中的作用的基本问题得以研究。初步数据表明，它们利用硫氧化产生的能量来吸收碳。该项目试图解决一个总体假设，即硫转化为整个水柱中的有机和无机碳循环提供了Arctic96BD- 19 gso谱系的能量。将测试三个具体的假设。Arctic96BD-19细胞吸收有机碳或固定无机碳，这取决于环境条件。Arctic96BD-19细胞通过形成四硫酸盐中间体或使用支链硫代硫酸盐氧化途径氧化硫代硫酸盐。Arctic96BD-19细胞是无处不在的硫氧化剂，通过太平洋西北部吸收有机和无机碳。将使用研究者纯培养物的实验室生长研究和比较基因组分析相结合的方法。基因组数据将用于确定Arctic96BD-19培养物是否具有将还原硫氧化为硫酸盐的遗传潜力（基于拥有已知的核心和辅助硫氧化基因），使用哪些潜在的氧化途径，以及它们是否可以固定无机碳。这些数据将通过确定最可能被利用的无机和有机化合物的形式来帮助指导生理学研究。更广泛的影响：海洋细菌是全球营养循环的关键参与者，但它们在生态系统中的许多个体和群落功能尚不清楚。未来的海洋学家将需要使用依赖于培养和不依赖于培养的方法来确定形成微生物群落和影响生物地球化学循环的代谢过程。一名女研究生和两名本科生将接受训练，使用分子和生理数据来解决假设。此外，该项目将通过数字电影向学生（特别是15至20岁的学生）介绍海洋学研究的独特和令人兴奋的方面，增加国家对海洋科学的曝光。华盛顿大学环境学院与艺术与科学学院之间的跨学院合作将培训数字媒体传播硕士学生制作短片，以鼓励年轻人对海洋学的兴趣。学生教育、科学进步和公众意识都是这个项目的重要组成部分。

Intellectual merit: The ocean serves an immense reservoir of carbon, nitrogen, phosphorus, sulfur, and other elements required for all life. The active and diverse microbial populations that inhabit the oceans are responsible for mediating nutrient transformations that maintain the chemistry of seawater. A recent study identified a ubiquitous group of marine bacteria from the Arctic96BD-19 gamma-proteobacterial sulfur oxidizer (GSO) lineage that is closely related to known sulfur oxidizing species that fix inorganic carbon and oxidize sulfide in low-oxygen waters. The potential for GSOs to use reduced forms of sulfur in oxygenated waters suggests that they are a keystone species that link the marine carbon and sulfur cycles. The only known isolates from the Arctic96BD-19 lineage of GSOs are now in culture, allowing fundamental questions about their roles in carbon and sulfur cycling to be investigated. Preliminary data suggest that they use energy from the oxidation of sulfur to assimilate carbon. This project seek to address the overarching hypothesis that sulfur transformations provide the Arctic96BD- 19 lineage of GSOs with energy for organic and inorganic carbon cycling throughout the water column. Three specific hypotheses will be tested.1. Arctic96BD-19 cells assimilate either organic carbon or fixes inorganic carbon, depending on environmental conditions.2. Arctic96BD-19 cells oxidize thiosulfate via formation of a tetrathionate intermediate, or using the branched thiosulfate oxidation pathway.3. Arctic96BD-19 cells are ubiquitous sulfur oxidizers that assimilate organic and inorganic carbon through the Pacific Northwest.A combination of laboratory growth studies of the investigator's pure cultures and comparative genomic analyses will be used. The genomic data will be used to determine whether the Arctic96BD-19 cultures possess the genetic potential to oxidize reduced sulfur to sulfate (based on possession of known core and ancillary sulfur oxidation genes), which potential oxidation pathways are used, and whether they can fix inorganic carbon. These data will help guide the physiology studies by determining the most likely forms of inorganic and organic compounds that can be utilized.Broader impacts: Marine bacteria are critical players in global nutrient cycles, but many of their individual and community functions in the ecosystem are not well understood. Future oceanographers will need to use cultivation-dependent and cultivation-independent methods to identify metabolic process that shape microbial communities and impact biogeochemical cycles. A female graduate student and two undergraduate students will be trained to use molecular and physiological data to address hypotheses. Additionally, this project will increase national exposure of ocean sciences through digital films that introduce students (particularly ages 15 to 20) to unique and exciting aspects of oceanographic research. A cross-college collaboration between the UW College of the Environment and the College of Arts and Sciences will train Master of Communication in Digital Media students to produce short films that encourage interest in oceanography among young people. Student education, scientific advancement, and public awareness are all important components of this project.