Modern-day, cyanobacteria-dominated, microbial mats living in oxygen-poor, sulfur-rich environments resemble life that may have oxygenated the early Earth. However, there is a major gap in our understanding of the functioning of cyanobacteria under anoxic and sulfidic conditions during Earth’s ancient oxygenation. Modern mat worlds are composed of motile filaments of microbes (cyanobacteria, diatoms and chemosynthetic bacteria and archaea) that variably use sunlight and chemicals in their daily routines and offer opportunities for discovering novel microorganisms and ecosystem processes. Daily or diel vertical migration (DVM) has been visually observed in the field, suggesting different microbes migrate vertically to the surface of the mat during daylight and nighttime. This project was aimed at unraveling the who, why and how of daily microbial migration through integration of microscopy, cultures, molecular approaches, and biogeochemical process measurements in response to changing gradients of light, sulfide and oxygen over the day-night cycle – and potentially explain O₂ production in modern cyanobacterial mats thriving in conditions mimicking early Earth.

During the last 3 years of the project, the Biddanda and Hamsher Labs at GVSU have worked with collaborator (Casamatta, UNF) addressing 3 central issues: (1) who is 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 ensuing project resulted in the following activities 1. Obtained underwater time-lapse images of diel vertical migration (DVM) revealing alternating waves of vertically migrating photosynthetic and chemosynthetic filaments that followed daily fluctuating light in microbial mats in Lake Huron’s sinkholes, 2. In two field expeditions, collected intact sediment cores with overlying mats for carrying out controlled experiments, 3. Corroborated DVM observations in the field with similar DVM observations in intact mats under simulated day-night conditions in the laboratory probing the geobiological controls on DVM by physico-chemical microprofiling under low-O₂, sulfidic conditions, and 4. Evaluated the taxa involved in DVM using macro- and microscopic imaging, culturing, genetics (metabarcoding and metatranscriptomics), and allelopathic studies.

These project activities have resulted in the following outcomes: 1. Conducted two field campaigns in Lake Huron and Florida Springs characterizing the habitats and collecting mat samples, 2. Tracked the synchronized DVM of mat microbes in the field and in simulated laboratory settings, 3. Carried out physico-chemical microprofiling of the mat-sediment complex to reveal light and chemical cues that govern DVM across mm distances, 4. Conducted genetic analysis and culture studies of mats to reveal new species and inter-species interactions – and archived the data at NSF’s DMO site, 5. Published, with open access, findings highlighting these outcomes including the notion that such synchronized diel movement, might have played a critical role in optimizing photosynthesis, chemosynthesis, carbon burial, and oxygenation during the Precambrian, 6. Placed the DVM of microbial mats into a broader geobiological context through comparisons with other globally distributed cyanobacterial mat systems such as terrestrial sulfur springs, 7. Generated compelling student projects, 8. Attracted public attention to the local, regional and global significance of our findings, and 9. Fueled active collaboration between two predominantly research in undergraduate institutions (RUI) and a NOAA National Marine Sanctuary.

Our project has revealed 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 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. Broadly speaking, this project has expanded our understanding of Earth’s biological and physiological diversity, recorded daily vertical migration of mat filaments that might represent some of the earliest daily mass movement of life on our planet, provided insight into novel and cryptic species within the mat ecosystem and evidence of interspecific interactions, revealed biogeographic trends, provided a promising window for peering into C burial and release of O₂ in early Earth, and identified a potential model system in our search for life in extraterrestrial waters – ample justification for conservation of extant life such as these found in the extreme environment refugia of the Earth.

Last Modified: 04/12/2024
Modified by: Bopaiah A Biddanda