Antarctic lake microbes survive in environments with a myriad of extreme conditions. Understanding microbial community structure and metabolic diversity in these stressful conditions is an underexplored topic in microbial ecology. Notably, these communities are largely dependent on photosynthesis to form the base of their food webs, and thus light availability has major implications on community survival and structure. Therefore, we evaluated the impact of extreme shade on Antarctic lake community biodiversity and productivity. We subjected enriched environmental cultures from Lakes Fryxell and Bonney to extreme shade for four weeks. To assess culture productivity, we monitored growth using cellular density measurements OD600nm and Countess cell count values, as well as photosynthetic activity using Fv/Fm, the measurement of the maximum PSII photochemical yield. We also performed 16S and 18S rRNA sequencing, a classic approach for determining taxonomy, to assess the impact of extreme shade on biodiversity and species composition between control and treated communities. Although the lakes had some similarities, our data revealed distinct differences; Lake Fryxell cultures showed higher photosynthetic productivity and growth compared to Lake Bonney cultures. Similarly, although both cultures subjected to extreme shade showed an enrichment in non-photosynthetic microbes; this trend was particularly pronounced in Lake Bonney. Additionally, the lake cultures differed in the microbial families they contained. Our data ultimately indicates a structural and functional transition of Antarctic lake communities in response to extreme shade that is partly dependent on lake origin. Identifying and analyzing these changes in community structure addresses fundamental microbial ecology questions about how environmental conditions influence microbes. Future work could further characterize these microbial relationships by analyzing metabolic functions or follow shifts in other abiotic factors due to the shade-dependent microbial activity. As future scientists, this project familiarized us with various methods of culturing, physiological measurement and analysis, and fundamental concepts of microbial ecological study.
Authors: Hope Kirby, Avery Imes
Faculty Advisor: Rachael Morgan-Kiss, Microbiology Department