Prokaryotic diversity in four microbial mats on the Fildes Peninsula, King George Island, maritime Antarctica

Most of Fildes Peninsula is ice-free during summer thereby allowing for formation of networks of creeks with meltwater from Collins Glacier and snowmelt. A variety of benthic microbial mats develop within these creeks. The composition of these microbial communities has not been studied in detail. In this report, clone libraries of bacterial and cyanobacterial 16S rRNA genes were used to describe the microbial community structure of four mats near a shoreline of Drake Passage. Samples were collected from four microbial mats, two at an early developmental stage (December) and two collected latter in late summer (April). Sequence analysis showed that filamentous Cyanobacteria, Alphaproteobacteria, and Betaproteobacteria were the most abundant ribotypes. Diversity indices were comparable for the four mats. Bacterial libraries from mat samples collected in December represented primarily Alphaproteobacterial and Betaproteobacterial ribotypes. In contrast, filamentous Cyanobacteria as well as Alphaproteobacteria were most abundant in libraries derived from samples collected in April. Differences in relative abundances may reflect the succession of microbial communities during the austral summer. Composition of cyanobacterial orders in bacterial libraries obtained from mats collected in late summer were different compared with their corresponding cyanobacterial libraries. This may be the result of divergence in primer specificities. Nostocales, Oscillatoriales, and Synechococcales orders were the dominant ribotypes represented in cyanobacterial libraries. Some taxa of cyanobacteria identified using this strategy coincided with previous studies of others in the same region using microscopic techniques. Future work should combine microscopy, culture-dependent and culture-independent strategies to better describe microbial mats in maritime Antarctica.