As in various other natural environments, the mixed communities of microbes occupying the Antarctic lakes are marked by dynamic interactions between two important groups of microorganisms, the protists and the heterotrophic bacteria. The community structure in the lake habitat is composed of microorganisms that operate a simple food web in a physically and chemically stratified water column permanently covered by ice. Lake Fryxell, located in the McMurdo Dry Valleys of Antarctica, hosts a diverse community of algae and heterotrophic bacteria that survive under harsh conditions, including permanent low temperatures. Our study focused on the role of heat stress on microbial communities isolated from Lake Fryxell. First, the mixed enrichment cultures were exposed to short-term heat stress, having been incubated at 24°C for 24 hours. Second, in-vivo physiology and growth measurements were conducted. Lastly, sequencing of 16S and 18S rRNA taxonomic genes yielded phylogenetic analyses of the bacteria and eukarya communities. Bacteria in the no-stress control group had greater exponential growth rates than the heat-treated samples. In contrast, phytoplankton count increased after heat exposure. 16S rRNA amplicon sequencing data revealed changes in the community structure at the class level, with a decrease in the abundance of Gammaproteobacteria in heat-treated cultures compared to the no-stress control group. Rarefaction curves for both 16S and 18S OTUs revealed that the heat stress group was less diverse than both original cultures and control groups. Our results demonstrate that exposure to heat induces growth in bacterial communities isolated from Lake Fryxell while having a negative effect on the alpha diversity. These findings inform our understanding of the microbial community structure in Lake Fryxell, enabling further investigation into the diverse and complex interactions between bacterial and eukaryotic communities in extreme habitats. The combination of laboratory and analytical techniques utilized in this project provided experience that will be beneficial in our skill development as future physician-investigators.
Authors: Rakhsha Khatri, Valerie Thompson
Faculty Advisor:Rachael Morgan-Kiss, Microbiology
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