Sublithic bacteria associated with Antarctic quartz stones

Quartz stone sublithic cyanobacterial communities are common throughout the Vestfold Hills, Eastern Antarctica (68°S 78°E) contributing biomass in areas otherwise devoid of any type of vegetation. In this study, the sublithic microbial community and underlying soil was investigated using a variety of traditional and molecular methods. Although direct epifluorescent counts of the sublithic growth (average 1.1 x 109 cells g-1 dry weight) and underlying soil (0.5 x 109 cells g-1 dry weight) were similar, sublith viable counts (2.1 x 107 cfu g-1 dry weight) were on average 3-orders of magnitude higher in the subliths. Enrichment and molecular analyses revealed the predominate cyanobacteria were non-halophilic, able to grow optimally at 15-20°C, and were related to the Phormidium subgroup with several distinct morphotypes and phylotypes present. Sublithic heterotrophic bacterial populations and those of underlying soils included mostly psychrotolerant taxa typical of Antarctic soil. However, psychrophilic and halophilic bacteria, mostly members of the alpha subdivision of the Proteobacteria and the order Cytophagales, were abundant in the sublithic growth film (20-40% of the viable count and about 50% of isolated individual taxa) but absent from underlying soils. It is suggested that quartz stone subliths might constitute a 'refuge' for psychrophilic bacteria.