Diverse underwater communities of cyanobacteria and other microorganisms are capable of withstanding drastic changes in salinity.
The microbial mat communities—multi-layered sheets of bacteria and archaea that grow at the interface between submerged, moist or even desiccated surfaces—in a remote lake near the border with Canada are relatively stable, despite weathering a 10-fold increase in salinity over the summer months. The composition of the microorganisms seemed to respond more to changes in available light than changes in salinity.
This is the first time that the microbial mats in Hot Lake have been studied in detail. The findings indicate that a complex relationship between the organisms that make up the mat is responsible for the annual buildup, maintenance and eventual breakdown of the mats.
Hot Lake, located in northern Washington State, is home to a seasonal community of microorganisms that form dense mats on the floor of the lake every summer, but disintegrate over the winter. Snowmelt and rain replenish the water every spring, but as water evaporates over the summer, the salinity of the lake increased 10-fold.
The researchers found that, surprisingly, the composition of the microbial communities didn’t change much in response to drastic changes in salinity. The diversity of microorganisms only started to drop in October. The researchers observed that the diversity of the bacteria at the bottom of the mat took a nosedive first.
They propose that waning light in autumn makes it harder for the cyanobacteria above to produce enough organic compounds to feed the rich bacterial community living underneath it. The bacteria starve to death and without them and the mat begins to fall apart.
It’s possible that the drop in bacterial density is a delayed response to trying to survive in a high salinity environment, but understanding how this microbial community changes over time will require additional samples from a variety of locations in the lake, collected more frequently over the year. Nevertheless, the researchers note that the data generated for this publication serves as a solid genomic foundation for understanding microbial diversity and function in extreme habitats, particularly the process of carbon capture, via CO2 fixation by autotrophs—primary producers—those microorganisms that synthesize organic compounds from their surroundings.
The study, led by James Fredrickson of the Pacific Northwest National Laboratory, was part of a Community Sequencing Project that was started in 2012 and also represents a collaboration between JGI and another DOE national user facility, PNNL’s Environmental Molecular Sciences Laboratory.
Pacific Northwest National Laboratory
DOE Office of Science, Office of Biological and Environmental Research
Lindemann SR, et al, (2013) The Epsomitic Phototrophic Microbial Mat of Hot Lake, Washington: Community Structural Responses to Seasonal Cycling. Front. Microbio. 4:323.