Lake Fryxell is a perennially ice-covered lake located in the McMurdo Dry Valley, Antarctica. Due to harsh conditions such as low temperature and light, its food web is composed entirely of microbes. In this project, the goal was to investigate the composition of Lake Fryxell’s microbial communities when placed under extreme shade as the abiotic stressor. Community health was evaluated by monitoring growth and photosynthetic efficiency in the enrichment cultures. After four weeks of growth, cultures were filtered; DNA was extracted and sequenced to analyze phylogenetic make-up. The cultures grown under extreme shade showed lower photosynthetic activity than the control, and additionally, photosynthetic efficiency in both enrichment culture groups was lower than that of the pure cultures consisting of only algae. Phylogenetic diversity increased in the shaded cultures, while the relative abundance of green algae decreased. Taken together, this suggests that while phototrophs from Lake Fryxell can adapt to extreme shade in pure culture, they cannot compete with other organisms for resources in enrichment cultures. The family Neobodonida, composed of heterotrophic microbes, saw a 300% increase in relative abundance under extreme shade compared to the control, providing an example of a microbe that can outcompete green algae. It can be concluded that while phototrophic organisms remain dominant in Lake Fryxell samples under normal conditions, during extreme shade conditions their relative abundance is adversely affected by the lack of light. Drastic differences between community composition of shaded and control cultures were not observed, which is expected, seeing as Lake Fryxell is naturally a low light environment. Given this regular low light condition, the starting samples’ microbial composition likely already reflected some of the implications of the abiotic stress. Future studies could use microscopy and flow cytometry to determine if algae-bacterial interactions occur within enrichment cultures and how these interactions might impact the community structure compared to species grown in isolation.
Authors: Susanna D’Silva, Sydney Palmer
Faculty Advisor: Rachael Morgan-Kiss, Microbiology
Graduate Student Advisor: Trevor Powell, Microbiology and Rochelle Pereira, Microbiology
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