N-185. Inter-Annual Stability of Microbial Community Composition in Three Perennially Ice-Covered Lake Systems in the McMurdo Dry Valleys, Antarctica

W. Foo, S-K. Han, B. Lanoil;
Univ. of California, Riverside, CA.

The highly stratified perennially ice-covered lakes of the McMurdo Dry Valleys, Antarctica (MCM)experience reduced light penetration, decoupled light-dark cycles, no vertical mixing, and minimal sediment deposition. As part of our ongoing efforts to determine the interactions between the microbial communities and the highly unusual geochemistry of the MCM, we used bacterial 16S rRNA gene DGGE to characterize the diversity and distribution of microorganisms in the water columns of east lobe Bonney (ELB), west lobe Bonney (WLB), and Fryxell (FRX) lakes across three years: 2003, 2004, and 2007. Cluster analysis indicated that while the surface layers of all three systems are related to each other, the bottom waters are distinct, both from each other and from surface waters. For most samples, cluster analysis also indicated that the microbial diversity in these systems is highly stable on an annual basis though the relative abundance of individual OTUs based upon DGGE band intensity varied between the three years. The exceptions to this pattern are ELB 13 m and FRX 12 m. For these two samples near the chemocline of their respective systems, the DGGE banding pattern shifted in similarity from the surface waters to the bottom waters. This fluctuation may be attributed to variation in the chemical composition of the water column at these specific depths. Canonical correspondence analysis (CCA) based upon the 2003 clone library results and the biogeochemical data explain 40.9% of the variance between samples. Though salinity is largely responsible for the presence of a chemocline in these lake systems, it was not a major factor for distinguishing the variance between these samples in CCA. Rather the bottom waters of ELB were differentiated through positive correlations with NO2 and NO3, whereas the bottom waters of FRX were differentiated through positive correlations with silicon and soluble reactive phosphorus. This study is the first to address inter-annual variability of the microbial community composition of the McMurdo Dry Valley lakes.