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The structure and succession of copper-resistant bacterial communities from the soils of the King George island 1
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Hanna Tashyreva , Natalia Belkova Department of Extremophilic Microorganism Biology, Zabolotny Institute of Microbiology and Virology, 2 National Academy of Science of Ukraine, Kyiv, Ukraine, Laboratory of Aquatic Microbiology, Limnological Institute SB RAS , Irkutsk, Russia 1
(Email:
[email protected]) Abiotic factors are believed to influence the structure of microbial communities in terrestrial Antarctic environments, while trace metals also play important role in shaping the community variation. Copper can be one of such factors since it enters into environments during rock weathering processes and appears to be an abundant anthropogenic pollutant. Five soil samples were collected on ice-free areas of Fildes Peninsula (King George Island, Antarctica) to discover changes in the microbial communities under the action of copper ions. We studied the formation of the metal-resistant microbial community and it‘s succession in the presence of 200 mg/L Cu(II) ions during 6 days by using 454 pyrosequencing of V4-V8 variable regions of 16S rDNA amplicons. Metal-resistant communities showed lower heterogeneity of their structure compared to natural diversity of the soil bacterial communities (19-21 phyla) and included 11 phyla (3-8 phyla in each community) Proteobacteria, Firmicutes, Verrucomicrobia, Actinobacteria, Gemmatimonadetes, Acidobacteria, Bacteroidetes, Cyanobacteria, Planctomycetes, Chloroflexi and Nitrospira. The dominant part of the Cu-resistant community was bacteria detected in the natural soil samples only as low-abundant or unique sequences – members of the genera Pseudomonas, Ralstonia, Microbacterium, Caulobacter, Methylobacterium, Sphingomonas and Bacillus, while genera Massilia, Polaromonas, Brevundimonas, Rhodococcus and class Spartobacteria, which were abundant in natural communities, accounted for only a smaller proportion. We have observed 3 different scenarios of succession in Antarctic Cu-resistant bacterial communities: 1) rapid increase in the proportion followed by complete dominance of Gammaproteobacteria; 2) shift of the dominant phylum from Proteobacteria to Firmicutes; 3) gradual increase in the proportion of Actinobacteria during the community incubation. Diversity of the Cu-resistant community significantly varied and did not depend on the initial diversity of the soil sample. Diversity by Shannon‘s index in natural communities was in range 4.4-5.9 while for Cu-resistant communities it varied from 1.9 to 0.2. At early stages of the community growth at the 3% evolutionary distance were detected 22-62 OTUs depending on the sampling site (the highest in samples selected on slopes with rich moss and lichen cover). During the growth and succession of the microbial community the tendency to decreasing diversity to 15-40 OTUs was observed. At the same time, at late stages surprisingly high diversity of Cu-resistant anaerobic bacteria that belong to Clostridia class – Tissierella, Clostridium sensu stricto and Anaerosporobacter, was found. Among them, unclassified bacteria of family Ruminococcaceae were the dominant phylotypes that accounted for 30% of total reads. Three typical strains representing Cu-resistant Antarctic soil bacterial communities were isolated and identified as Ralstonia pickettii KG85, Pseudomonas veronii KG147 and Microbacterium laevaniformans KG138. The findings of this study contribute to knowledge about the adaptation of highly heterogeneous microbial communities and their changes under pressure of extreme natural and anthropogenic abiotic factors.
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