Biogeophysical interactions control the formation of iron oxide mat microbial communities in acidic geothermal springs
Ecological succession of microbial communities in their natural environment is a complex process that is not well understood. Microbial ecosystems are difficult to examine in part due to the small size of microbial cells and small scale of key biogeochemical processes, where microscopy and molecular techniques must be employed to track the activities microorganisms in their environment. However, modern molecular (e.g., community genomics) and microscopy techniques (e.g., fluorescence in situ hybridization) have allowed for microbial communities to be studied in greater detail. This study focused on the successional development of iron oxide mat microbial ecosystems that occur within high temperature (65-75° C), acidic (pH ~ 3), geothermal spring outflow channels in Yellowstone National Park. These iron oxide microbial communities contain both microorganisms from the domains Archaea and Bacteria that either use inorganic sources of energy (e.g., iron) and fix carbon dioxide (lithoautotrophs) or utilize organic sources of energy and do not fix carbon dioxide (organoheterotrophs). Glass microscope slides were placed in the outflow channel to provide a substrate for microbial growth and total iron deposited was measured as well as community development by using 16S rRNA genes. Results suggest inter-spring variation of iron deposition likely caused by differences in flow and seasonal variations due to increases UV radiation causing an increase in viral pressure in summer months. Lithoautotrophs were often found to be more dominant in early stages of community development, whereas organoheterotrophs were more abundant when the community reached a pseudo-steady state. Thus, iron oxide microbial community development is a dynamic process.