CAREER: A phylogenetic and functional understanding of microbial sulfur cycling in oxygen minimum zones

氧气浓度显著影响海洋生态系统的群落结构和功能。在低氧水域，包括主要的海洋最低含氧区(OMZ)，生物多样性由一个复杂的微生物群落主导，这些微生物的厌氧代谢在全球氮和碳循环的关键步骤中起中介作用。令人惊讶的是，新的证据表明，OMZ还支持能够利用无机硫化合物进行能量代谢的各种微生物。这种组合似乎既包括硫氧化自养生物，也包括硫酸盐还原异养生物，这表明一个活跃的硫循环在有机碳输入和矿化中具有潜在的重要作用，以及与OMZ氮循环的关键联系。我们对推动OMZ硫循环的微生物的知识主要基于单一细菌谱系的元基因组(SUP05)和对诊断标记基因的调查，到目前为止，这些基因只针对全球海洋中多样化的低氧区域的一部分。硫代谢微生物在OMZ水柱中的代谢多样性、活性和生物地理分布在很大程度上仍未得到探索。该项目采用分子和实验相结合的方法，对微生物在最低氧区硫循环的生理和系统发生基础进行了严格的研究。结合目标元基因组学与基因表达谱、微观世界加硫实验和富集化培养，PI将表征两个不同海洋和生态低氧区的硫代谢微生物：墨西哥附近的东热带北太平洋(ETNP)OMZ，它代表着世界上最大的永久性OMZ；以及墨西哥湾(GOM)的季节性低氧“死区”。具体地说，他们将检验这样的假设：1)ETNP OMZ中有大量的硫氧化和还原浮游细菌，2)是低氧GOM的次要成分，但当氧气减少和硫化物增加时，活性和丰度增加，3)在垂直剖面、OMZ之间和对环境梯度的响应中，功能基因含量和系统发育多样性显示出生物地理差异。预计OMZ将扩大以应对未来的气候变化，这使得从整体上了解低氧区的生物学是当务之急。该项目将建立一个全面的框架来研究海洋浮游细菌的基因组学和生理学，这一功能群在生态上具有重要意义，但特征不佳。结果将与来自永久东热带南太平洋(ETSP)OMZ和第二个季节性OMZ(Saanich Inlet)的现有元基因组数据进行分析，从而建立一个比较基础，以描述远洋硫代谢微生物的生态分布及其在OMZ群落代谢中的相对作用。广泛的影响海洋科学研究将被用作跨多个学术水平加强科学教育的平台。将与佐治亚理工学院的K-12教育工作者和教师发展专家合作举办海洋科学夏季讲习班(SWIFS)。为期5天的游泳项目包括在斯基德韦海洋研究所的2天，将邀请研究生和佐治亚理工学院的研究人员培训当地教师，将海洋科学的关键主题与中学地球科学教育的新国家标准结合起来。此外，通过与莫尔豪斯学院和斯佩尔曼学院的合作，该项目为暑期实习提供资金，以提高少数族裔学生在本科海洋科学和生物信息学研究中的代表性。将在佐治亚理工学院设立一个海洋基因组学研究生工作组，为海洋基因组学跨学科领域的培训制定和实施新的指导方针。佐治亚理工学院将开设一门新课程，为科学家写作，以促进研究生的专业发展。它将使用有组织的、同行驱动的练习，让学生掌握在科学领域取得成功所必需的批判性写作和演讲技能--佐治亚理工学院严重缺乏这样的课程。通过以上概述的活动，这一职业项目不仅将建立一个研究小组，致力于确定海洋微生物生态系统中具有生态意义但又复杂的组成部分的特征，而且还将建立一个坚实的基础，通过这个基础，国际海洋科学协会可以利用他的工作成果来培训和激励未来几代海洋科学家。

Oxygen concentration significantly impacts the community structure and function of marine ecosystems. In waters with low oxygen, including the major marine oxygen minimum zones (OMZs), biological diversity is dominated by a complex community of microorganisms whose anaerobic metabolisms mediate key steps in global nitrogen and carbon cycles. Surprisingly, new evidence indicates that OMZs also support diverse microorganisms capable of utilizing inorganic sulfur compounds for energy metabolism. This assemblage appears to include both sulfur-oxidizing autotrophs and sulfate-reducing heterotrophs, suggesting an active sulfur cycle with potentially substantial roles in organic carbon input and mineralization, as well as critical links to the OMZ nitrogen cycle. Our knowledge of the microorganisms driving OMZ sulfur cycling is based largely on the metagenome of a single bacterial lineage (SUP05) and on surveys of diagnostic marker genes, which have thus far targeted only a subset of the diverse low-oxygen regions in the global ocean. The metabolic diversity, activity, and biogeographic distribution of sulfur-metabolizing microorganisms in the OMZ water column remain largely unexplored. This project uses an integrated molecular and experimental approach to critically examine the physiological and phylogenetic basis of microbial sulfur cycling in oxygen minimum zones. Combining targeted metagenomics with gene expression profiling, microcosm sulfur-addition experiments, and enrichment culturing, the PI will characterize sulfur-metabolizing microorganisms in two oceanographically and ecologically distinct low-oxygen regions: the Eastern Tropical North Pacific (ETNP) OMZ off Mexico, which represents the largest permanent OMZ in the world, and the seasonally hypoxic "dead zone" in the Gulf of Mexico (GOM). Specifically, they will test the hypotheses that sulfur- oxidizing and -reducing bacterioplankton 1) are abundant and transcriptionally active in the ETNP OMZ, 2) are minor components of the hypoxic GOM, but increase in activity and abundance when oxygen decreases and sulfide increases, and 3) exhibit biogeographic variation in functional gene content and phylogenetic diversity over vertical profiles, among OMZs, and in response to environmental gradients. OMZs are predicted to expand in response to future climate change, making it imperative to holistically understand the biology of low-oxygen regions. This project will establish a comprehensive framework for studying the genomics and physiology of an ecologically important, but poorly characterized, functional group(s) of marine bacterioplankton in OMZs. Results will be analyzed relative to existing metagenomic data from the permanent Eastern Tropical South Pacific (ETSP) OMZ, and a second seasonal OMZ (Saanich Inlet), thereby establishing a comparative basis for describing the ecological distribution of pelagic sulfur-metabolizing microorganisms and their relative role in OMZ community metabolism.Broader ImpactsMarine science research will be used as a platform for enhancing science education across multiple academic levels. A Summer Workshop in Marine Science (SWIMS) will be developed in collaboration with K-12 educators and teacher-development experts at Georgia Tech. The 5-day SWIMS program, which includes 2 days at the Skidaway Institute of Oceanography, will engage graduate students and Georgia Tech researchers in training local teachers to merge key topics in marine science with new national standards in middle school Earth Science education. In addition, through a partnership with Morehouse and Spelman Colleges, this project funds summer internships to enhance representation of minority students in undergraduate marine science and bioinformatics research. A PI-graduate student working group is to be established at Georgia Tech to develop and implement new guidelines for training in the cross-disciplinary field of marine genomics. A new course will be created at Georgia Tech, Writing for Scientists, to enhance the professional development of graduate students. It will use structured, peer-driven exercises to equip students with the critical writing and speaking skills necessary for success in science - such a course is critically lacking at Georgia Tech. Through the activities outlined above, this CAREER project will not only establish a research group dedicated to characterizing an ecologically significant, but cryptic, component of the marine microbial ecosystem, but will also develop a strong foundation through which the PI can use the results of his work to train and motivate future generations of marine scientists.