Autotrophy to Heterotrophy: Shift in Bacterial Functions During the Melt Season in Antarctic Cryoconite Holes.

Microbes residing in cryoconite holes (debris, water, and nutrient-rich ecosystems) on the glacier surface actively participate in carbon and nutrient cycling. Not much is known about how these communities and their functions change during the summer melt-season when intense ablation and runoff alter the influx and outflux of nutrients and microbes. Here, we use high-throughput-amplicon sequencing, predictive metabolic tools and Phenotype MicroArray techniques to track changes in bacterial communities and functions in cryoconite holes in a coastal Antarctic site and the surrounding fjord, during the summer season. The bacterial diversity in cryoconite hole meltwater was predominantly composed of heterotrophs (Proteobacteria) throughout the season. The associated functional potentials were related to heterotrophic-assimilatory and -dissimilatory pathways. Autotrophic Cyanobacterial lineages dominated the debris community at the beginning and end of summer, while heterotrophic Bacteroidota- and Proteobacteria-related phyla increased during the peak melt period. Predictive functional analyses based on taxonomy show a shift from predominantly phototrophy-related functions to heterotrophic assimilatory pathways as the melt-season progressed. This shift from autotrophic to heterotrophic communities within cryoconite holes can affect carbon drawdown and nutrient liberation from the glacier surface during the summer. In addition, the flushing out and export of cryoconite hole communities to the fjord could influence the biogeochemical dynamics of the fjord ecosystem.

Microbial communities and their potential for degradation of dissolved organic carbon in cryoconite hole environments of Himalaya and Antarctica.

Cryoconite holes (cylindrical melt-holes on the glacier surface) are important hydrological and biological systems within glacial environments that support diverse microbial communities and biogeochemical processes. This study describes retrievable heterotrophic microbes in cryoconite hole water from three geographically distinct sites in Antarctica, and a Himalayan glacier, along with their potential to degrade organic compounds found in these environments. Microcosm experiments (22 days) show that 13-60% of the dissolved organic carbon in the water within cryoconite holes is bio-available to resident microbes. Biodegradation tests of organic compounds such as lactate, acetate, formate, propionate and oxalate that are present in cryoconite hole water show that microbes have good potential to metabolize the compounds tested. Substrate utilization tests on Biolog Ecoplate show that microbial communities in the Himalayan samples are able to oxidize a diverse array of organic substrates including carbohydrates, carboxylic acids, amino acids, amines/amides and polymers, while Antarctic communities generally utilized complex polymers. In addition, as determined by the extracellular enzyme activities, majority of the microbes (82%, total of 355) isolated in this study (Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria and Basidiomycota) had ability to degrade a variety of compounds such as proteins, lipids, carbohydrates, cellulose and lignin that are documented to be present within cryoconite holes. Thus, microbial communities have good potential to metabolize organic compounds found in the cryoconite hole environment, thereby influencing the water chemistry in these holes. Moreover, microbes exported downstream during melting and flushing of cryoconite holes may participate in carbon cycling processes in recipient ecosystems.

Spatial variability and possible sources of acetate and formate in the surface snow of East Antarctica.

Spatial trends of acetate (Ac-) and formate (Fo-) were determined in surface snow samples along a coastal-inland transect (180km) in the ice cap region at Princess Elizabeth Land and along a coastal transect in the Amery Ice Shelf (130km), East Antarctica. Variations in both Ac- and Fo- seem to be unrelated to the acidity of snow. Ionic balance determined for the snow samples indicate the availability of HNO3 that could undergo photolysis to produce hydroxyl radical (OH), one of the major reactants involved in oxidation reactions with organic matter. The strong positive correlations between Ac- and NO3- in snow from both regions indicate that NO3- mediated OH-oxidation of organic compounds in snow could be an important source of Ac- within the snowpack. On the other hand, negative correlation between Fo- and NO3- might indicate that sources other than OH-oxidation of organic matter may be dominant in the case of Fo-. Higher Ac- concentrations in the ice cap compared to the ice shelf correspond with long-range transport of biomass burning emissions to the ice cap region. Interaction of Ac- and Fo- with alkaline minerals could lead to their stability in the snowpack and minimize their loss from the snow surface. Resident microbial communities could also influence the budget of the carboxylic acids in snow.