Collaborative Research: RUI: OCE-BO: Biogeochemistry of diurnal vertical migration in microbial mats of Lake Huron’s sinkholes.

生活在休伦湖下天坑底部的现代微生物垫经历了一个类似于地球早期生命的贫氧、富硫环境。这些垫子世界由移动的微生物细丝主导，它们在日常生活中可变地利用阳光和化学物质，为发现新的微生物和生态系统过程提供了机会。最近，在野外观察到了复杂的每日垂直迁移模式，这表明不同的微生物在白天和夜间垂直迁移到垫子的表面。该项目正在通过整合显微镜、培养、分子方法和过程速率测量来揭示谁、为什么以及如何每日微生物迁移，以响应光、硫化物和氧气在昼夜循环中的变化梯度。该项目通过与陆地泉水和冰盖覆盖的南极湖泊等全球分布的其他蓝藻垫子系统的比较，将微生物垫子的垂直迁徙置于更广泛的地球生物学背景下。此外，多种多样的天坑垫子可能会成为机器人探索类似外星水域生命的有用工作模型，比如木星的欧罗巴或土星的土卫二。这个项目产生了令人信服的学生项目，吸引了公众的想象力，并促进了两个以本科生为主的机构和国家海洋保护区之间的积极合作。蓝藻在硫化、低O2-条件下的功能是我们过去对地球氧合作用理解的一个主要缺口。最近，收集到的Diel垂直迁移(DVM)的延时图像显示，随着休伦湖天坑中微生物垫上每日波动的光线，垂直迁移的光合作用和化学合成细丝的交替波；在实验室模拟昼夜条件下的观察结果证实了完整的垫子。这种同步的海底运动，可能在优化前寒武纪的光合作用、化学合成、碳埋藏和氧化作用方面发挥了关键作用。该项目正在评估DVM所涉及的分类群，并利用宏观和微观成像、物理化学显微图谱、培养、遗传学和化感作用研究，探索低O2、硫化条件下DVM的地球生物控制。正在解决三个中心问题：(1)哪些分类群负责DVM？(2)它们如何以及为什么执行DVM？以及(3)DVM社区和活动协同效应的生态系统后果是什么？该项目正在揭示特定的微生物种群、代谢途径和地球化学过程，这些过程支撑着MAT在生物循环中的生物地球化学。研究微生物群落在微米尺度的过程中具有规律和可测量的日节律，为微生物垫生物地球化学的分子基础提供了前所未有的视角，并为未来旨在重新定义自养群落在古代海洋和现代生态系统中的作用的研究奠定了基础。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Modern-day microbial mats living on the bottom of sinkholes underneath Lake Huron experience an oxygen-poor, sulfur-rich environment resembling life on early Earth. These mat worlds are dominated by motile filaments of microbes that variably use sunlight and chemicals in their daily routines and offer opportunities for discovering novel microorganisms and ecosystem processes. Recently, complex patterns of daily vertical migration has been observed in the field, suggesting different microbes migrate vertically to the surface of the mat during daylight and nighttime. This project is unraveling the who, why and how of daily microbial migration through integration of microscopy, cultures, molecular approaches, and process rate measurements in response to changing gradients of light, sulfide and oxygen over the day-night cycle. This project places the vertical migration of microbial mats into a broader geobiological context through comparisons with other globally distributed cyanobacterial mat systems such as terrestrial springs and ice-covered Antarctic lakes. Furthermore, the diverse and versatile sinkhole mats may serve as a useful working model for robotic exploration of similar life in extraterrestrial waters like that of Jupiter’s Europa or Saturn’s Enceladus. This project is generating compelling student projects, attracting public imagination, and fueling active collaboration between two predominantly undergraduate institutions and a National Marine Sanctuary.The functioning of cyanobacteria under sulfidic, low O2-conditions is a major gap in our understanding of Earth’s oxygenation in the past. Recently, time-lapse images of diel vertical migration (DVM) were collected revealing alternating waves of vertically migrating photosynthetic and chemosynthetic filaments that followed daily fluctuating light in microbial mats in Lake Huron’s sinkholes; observations corroborated with intact mats under simulated day-night conditions in the laboratory. Such synchronized diel movement, might have played a critical role in optimizing photosynthesis, chemosynthesis, carbon burial, and oxygenation during the Precambrian. This project is evaluating the taxa involved in DVM and is probing geobiological controls on DVM under low-O2, sulfidic conditions using macro- and microscopic imaging, physico-chemical microprofiling, culturing, genetics, and allelopathic studies. Three central issues are being addressed: (1) what taxa are responsible for the DVM? (2) how and why do they perform DVM? and (3) what are the ecosystem consequences of DVM community and activity synergies? The project is revealing specific microbial populations, metabolic pathways, and geochemical processes that underpin mat biogeochemistry over the diel cycle. Studying microbial communities that have regular and measurable daily rhythms in processes that can also be tracked at micrometer scales yields an unprecedented view of the molecular underpinnings of microbial mat biogeochemistry and lays the foundation for future studies aimed at re-defining the role of autotrophic communities in ancient seas and modern ecosystems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.