The Abundance and Taxonomic Diversity of Filterable Forms of Bacteria during Succession in the Soils of Antarctica (Bunger Hills).

Andrey V Dolgih,Ilya G Shorkunov,Alina G Kudinova,Olga A Maslova,Mayya A Petrova,Nikita S Mergelov

doi:10.3390/microorganisms9081728

Abstract

Previous studies have shown that a significant part of the bacterial communities of Antarctic soils is represented by cells passing through filters with pore sizes of 0.2 µm. These results raised new research questions about the composition and diversity of the filterable forms of bacteria (FFB) in Antarctic soils and their role in the adaptation of bacteria to the extreme living conditions. To answer such questions, we analyzed the succession of bacterial communities during incubation of Antarctic soil samples from the Bunger Hills at increased humidity and positive temperatures (5 °C and 20 °C). We determined the total number of viable cells by fluorescence microscopy in all samples and assessed the taxonomic diversity of bacteria by next-generation sequencing of the 16S rRNA gene region. Our results have shown that at those checkpoints where the total number of cells reached the maximum, the FFB fraction reached its minimum, and vice versa. We did not observe significant changes in taxonomic diversity in the soil bacterial communities during succession. During our study, we found that the soil bacterial communities as a whole and the FFB fraction consist of almost the same phylogenetic groups. We suppose rapid transition of the cells of the active part of the bacterial population to small dormant forms is one of the survival strategies in extreme conditions and contributes to the stable functioning of microbial communities in Antarctic soils.

Highlights

Typic Haploturbel sample (BB 63–48), the organo-mineral material was organized in mmsized granules that often had a coarse mineral grain in their core and a mixture of clays, carbonates and other salts at a periphery; the latter were mainly responsible for a lighter color in comparison to the other two samples (Figure 2e,f)
In the Typic Haploturbel sample (BB 63–48), the organo-mineral material was organized in mm-sized granules that often had a coarse mineral grain in their6core of 22 and a mixture of clays, carbonates and other salts at a periphery; the latter were mainly responsible for a lighter color in comparison to the other two samples (Figure 2e,f)
Since our results have shown the enrichment of the FFB fraction of Antarctic soils precisely by the phylum Proteobacteria, it is possible to expect that a significant part of the cells are just those slender filamentous forms of bacteria capable of

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Bacteria have a wide variety of survival strategies under adverse conditions such as low temperatures, ultraviolet radiation, low humidity, and nutrient deficiencies [1,2]. There is a hypothesis that in the soil, especially in the conditions of the nitrogen and carbon limitation, as well as in habitats with extremely low temperature, a significant part of the cells is dormant, which is often characterized by a decrease in cell size [3,4]. The bacterial strains isolated from permafrost are more prone to go into a dormant state in the form of ultra-small cells than strains of the same genera isolated from soils of temperate latitudes [5]

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