AME prepress abstract  -  doi: 10.3354/ame01813

Versatile photophysiology of compositionally similar cyanobacterial mat communities inhabiting submerged sinkholes of Lake Huron

Michael J. Snider*, Bopaiah A. Biddanda*, Morgan Lindback, Sharon L. Grim, Gregory J. Dick

*Email: snidemic@mail.gvsu.edu

ABSTRACT: Recently discovered submerged sinkholes in Lake Huron are high-sulfur, low-oxygen extreme environments for microbial life. In order to understand the relationship between the physical environment, photophysiology and community composition, we measured the physical conditions, photophysiological indices, and genetic diversity at 3 microbial mat sites bathed in high conductivity groundwater under a natural light gradient during 2012-2013. A strong seasonal trend prevailed at all sites, characterized by decreased photosynthetic yield (Fv’/Fm’) during the summer (0.25 – 0.40; April – August) and increased yield during the winter (0.70 - 0.75; November – March). Chlorophyll a content varied seasonally in a similar manner to photosynthetic yield. All sites were dominated by >80% abundance of one cyanobacterial group – most closely related to Phormidium sp. Phycobilins (phycocyanin and phycoerythrin) were consistently higher in concentration than chlorophyll. Photosynthetic yield was statistically indistinguishable between sites, suggesting that these mat communities are able to acclimate across a wide range of photosynthetically active radiation (PAR). Interestingly, these cyanobacteria carried out oxygenic photosynthesis in the presence of in vitro H2S – further suggestive of their versatile photophysiologies under variable redox conditions. Collectively, our study provides insight into the adaptive capabilities of cyanobacteria by revealing how they photophysiologically respond to changes in the light climate and redox conditions, and are thereby able to inhabit a wide range of physico-chemical environments. Such versatile physiologies may have enabled their ancestors to thrive across a range of habitats in early Earth.