PS 3-29
Microbial communities of pinnacles in ice-covered Antarctic Lake Vanda
Lake Vanda is a perennially ice-covered lake in Wright Valley of the McMurdo Dry Valley region of Antarctica. Lake Vanda is stratified, with saline waters at the bottom and fresher waters near the top. The bottom waters are anoxic, while the fresher waters in the photic zone oxygen saturated. Throughout the photic zone, the lake floor is covered with thick microbial mats. The absence of disturbance and grazing metazoans makes Lake Vanda an environment reminiscent of the earth’s early biosphere. There has been some work on the water column biota, but little research on the benthic mats. Consistent features of the benthic mats in Lake Vanda are pinnacles, which vary in size and number throughout the photic zone. Larger pinnacles (~24 mm) were found at lower depths, and smaller pinnacles (~4 mm) were more abundant at shallow depths. Cross sections of the pinnacles show internal laminations, with characteristic pigmented layers consisting of outer orange/brown layers, followed by an inner green layer which transitions to pink toward the interior of the pinnacle. These layers were separated in the field, and analyzed separately using culture independent methods to gain an understanding of the variations in microbial content between layers.
Results/Conclusions
Cyanobacterial specific partial 16S rRNA gene analysis showed that pinnacles are dominated by filamentous cyanobacteria from the order Oscillatoriales, primarily Limnothrix, Leptolyngbya and Phormidium. Based on phylogenetic and BLASTn analysis, the taxa are most similar cyanobacteria found in other cold environments. Leptolynbya dominated all layers, whereas Phormidium was mainly abundant in the purple and green layers. This matches with microscopic observations, and suggests that Leptolynbya must play an important part in the formation of the cyanobacterial matrix and macroscopic structure of the pinnacles. Difference in pigmentation therefore did not reflect microbial communities, but a response to variable the levels in the pinnacle implying that these Antarctic cyanobacteria are all similarly well adapted to respond to a range of light conditions.