The evolution and proliferation of oxygenic photosynthesis in the form of cyanobacteria has fundamentally altered Earth and ultimately enabled the emergence of multicellular life. In the largely anoxic Precambrian environment, cyanobacteria likely first created oxygen hotspots in the arena for the evolution of OP, microbial mats, which eventually facilitated wide-spread atmospheric oxygen “whiffs” and finally the Great Oxidation Event (GOE). ). In the variable oxygen conditions after the GOE, cyanobacterial mats likely remained important sources of O2. There are however many open questions concerning the drivers of Earth’s redox evolution including the factors that might have controlled the net release of O2 from ancient microbial mats. Studying extant analogue microbial mats can reveal conceptual mechanisms that better constrain current models of ancient ecosystems. The cyanobacterial mats forming in the Middle Island Sinkhole, Michigan, are such modern analog of a Proterozoic low-oxygen ecosystem. We studied how the concerted operation of the main metabolic pathways within these mats affects net O2 production, mainly using microsensors. We found that the interaction of functionally diverse groups of microorganisms, namely cyanobacteria, sulfur oxidizing bacteria, diatoms, sulfate reducers and methanogens, shapes the rates of O2 release. Most notably, the O2 production was not predictable based on thermodynamic considerations because of specific adaptation mechanisms of the microbial groups to the dynamic mat environment. In such microbially engineered structures, the interaction of energetics, kinetics, mechanics, and microbial (mis)behavior can lead to counterintuitive feedback effects, ultimately shaping O2 accumulation. The unexpectedly complex regulation of O2 production might indicate that the ancient sources of O2, microbial mats and their inhabitants, hold the answers to some of major open questions about Earth’s oxygenation.

Geochemical and microbiological controls of oxygen production in cyanobacterial mats

253rd National Meeting (2017)

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