Microbes in Icy Systems: An interdisciplinary approach to characterize microbes in a humic free environment
Dissolved organic matter (DOM) plays an important role in conditioning the environment for microbes in aquatic ecosystems. DOM is comprised of organic compounds produced by the degradation of plant matter and microbial biomass, and microbial exudates. The absence of higher plants in Antarctica results in a DOM pool derived solely from microbial sources. Antarctic supraglacial streams, which form annually from glacial melt water, are particularly unique in their DOM signature. Analysis of a supraglacial stream on the Cotton Glacier, Antarctica has shown that the concentration of DOM is low (44-48 µM C), and fluorescence spectroscopy indicates a lack of humic signatures. In most natural waters, humic DOM absorbs visible and UV-light, buffers pH, and binds trace metals. The lack of humics may represent an environmental stressor influencing the microbial community. The Cotton Glacier stream contains bacterial cell abundances from 2.94 × 104–4.97 × 105 cells ml-1, and bacterial production from 58.8-293.2 ng C l-1 d-1. Phylogenetic analysis characterized these microorganisms as similar to those from other cryogenic systems (Proteobacteria and Bacteroidetes). A proteomic approach was developed to probe the adaptation techniques and metabolism of stream isolates in the absence of genomic data. This interdisciplinary coupling of proteomics, genomics, and microbial ecology allows us to study microbial adaptation to the absence of humics.