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

现代生活在休伦湖下天坑底部的微生物群经历了一个缺氧、富硫的环境，类似于早期地球上的生命。这些垫子世界由微生物的活动丝主导，这些微生物在日常生活中不同地使用阳光和化学物质，并为发现新的微生物和生态系统过程提供了机会。最近，在野外观察到复杂的日常垂直迁移模式，表明不同的微生物在白天和夜间垂直迁移到垫子表面。该项目通过整合显微镜、培养、分子方法和过程速率测量来响应昼夜循环中光、硫化物和氧气梯度的变化，揭示了日常微生物迁移的对象、原因和方式。该项目通过与其他全球分布的蓝藻席系统（如陆地泉和冰雪覆盖的南极湖泊）进行比较，将微生物席的垂直迁移置于更广泛的地理生物学背景下。此外，各种各样的天坑垫可以作为机器人探索地外水域类似生命的有用工作模型，比如木星的木卫二或土星的土卫二。这个项目产生了引人注目的学生项目，吸引了公众的想象力，并促进了两个主要的本科院校和国家海洋保护区之间的积极合作。蓝藻在硫化物、低氧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空白。最近，我们收集了diel垂直迁移（DVM）的延时图像，揭示了休伦湖天坑微生物垫中垂直迁移的光合和化学合成细丝的交替波。在实验室模拟昼夜条件下，完整的垫子证实了观察结果。这种同步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。本项目通过宏观和微观成像、理化微谱、培养、遗传学和化感研究，对低氧、硫化物条件下的DVM进行评估，并探索DVM的地球生物学控制。三个核心问题正在被解决：(1)哪些分类群对DVM负责？(2)他们如何以及为什么执行DVM？(3) DVM群落和活动协同效应对生态系统的影响是什么？该项目揭示了特定的微生物种群、代谢途径和地球化学过程，这些都是生物地球化学在生物循环中的基础。研究微生物群落的过程中具有规律和可测量的日常节奏，也可以在微米尺度上进行跟踪，从而为微生物垫生物地球化学的分子基础提供了前所未有的观点，并为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未来研究奠定了基础。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.