Cyanobacterial communities from alvar substrates on Drummond Island, Michigan

Background/Question/Methods

Despite its rarity, there is little research on the alvar habitat and in particular, associated microbial communities. Many unique species are adapted to the harsh alvar environment impacted by sporadic rainfall and large fluctuations in temperature. Alvars are areas of calcerous bedrock, typically calcite (CaCO₃) or dolomite (CaMg(CO₃)₂), with little to no soil or organic matter. The development of soil upon the alvar facilitates the transition from bare substrate to an environment that can support vascular plant growth. Cyanobacteria are some of the earliest colonizers of bedrock and are structurally and functionally important in soil development. Large filamentous cyanobacteria form matrices capable of trapping soil particles, retaining moisture, and preventing erosion. Cyanobacteria are also important in areas with little to no anthropogenic nitrogen inputs as a producer of fixed nitrogen that is needed by successional species. Alvar rock samples and soil crust samples were collected from two sites found on Drummond Island, Michigan. Samples were subject to microscopy to characterize the alvar material. Samples were enriched using liquid media with and without fixed nitrogen and cyanobacteria were identified using microscopy and 16S rRNA sequencing.

Results/Conclusions

Geochemical analysis of the alvar samples revealed that the two sites differ in the degree of weathering, but are geologically similar. Scanning electron microscopy with energy dispersive spectroscopy showed that both sites contained Mg making them both dolomite substrates. Endolithic and soil crust cyanobacteria were successfully cultivated from both alvar sites using a liquid cyanobacterial growth medium, BG-11. Lithic samples and soil crust enrichments were imaged using light and scanning electron microscopy revealing a diverse array of cyanobacterial species. Liquid enrichments primarily contained Leptolyngbya, Microcoleus, Nostoc, Calothrix and Oscillatoria spp. Molecular analysis of unenriched samples found some of the same species along with Chroococcidiopsis and Petalonema spp. A BLASTn search of 16S rRNA sequences found that a number of the organisms detected had closest relatives from species found in Antarctic and Colorado Plateau environments. Overall, the results of microscopy and molecular detection revealed a diverse array of cyanobacteria likely play an important role in developing and stabilizing the delicate soils of the alvar.