Taxonomic Diversity of Bacteria and Their Filterable Forms in the Soils of Eastern Antarctica (Larsemann Hills and Bunger Hills)

Abstract

Increasing interest in microbial communities of Arctic and Antarctic extreme environments, their taxonomic diversity, and forms and mechanisms of adaptation of inhabitants of Antarctic biotopes to extreme conditions determined the goal of the present work. Next generation sequencing of the 16S rRNA gene fragments was used to determine the taxonomic structure of microbial communities in soil samples from the Larsemann Hills and Bunger Hills. Revealed differences in the composition of predominant bacterial phyla and genera indicate that the type of the biotope developing on the soil surface and a combination of various physicochemical factors play a major role in formation of Antarctic microbial communities. High number of filterable forms of prokaryotes (FFP) was found in the communities. Analysis of the libraries of the 16S rRNA gene clones revealed that the FFP from three Larsemann Hills samples belonged to the phylum Proteobacteria. In all three samples, the dominant FFP group exhibited the highest similarity (99%) to an uncultured bacterial clone of the class Deltaproteobacteria revealed by assessment of bacterial diversity of rocks and groundwater of the Donghai County, China. The FFP capable of growth of standard nutrient media belonged to the phyla Actinobacteria, Bacteroidetes, Deinococcus-Thermus, Firmicutes, and Proteobacteria. Taking into account the data of high FFP number in the samples and their taxonomic composition, their significant contribution to stability of the bacterial composition of Antarctic soils may be suggested. The FFP fraction was mainly represented by bacterial dormant forms able to revert to active growth under favorable conditions. Rapid transition of a vegetative part of the population to small dormant forms under unfavorable conditions is probably one of the strategies enabling their survival in extreme environments. The FFP fraction also contained the cells belonging to novel bacterial species, probably ultramicrobacteria.