Bacteria of the Genus Shewanella from Radionuclide-Contaminated Groundwater

Abstract

Decommissioned surface repositories of liquid radioactive waste remain a potential source of groundwater pollution. Establishment of biogeochemical barriers results in decreased migration of both radioactive and toxic macro-components of the waste. The article presents the results of studying the composition of the microbial community of groundwater sampled in the area of a surface repository for liquid radioactive waste. High-throughput sequencing of the 16S rRNA genes revealed the dominant and minor components of the community, among which were found bacteria of the genus Shewanella. Isolated pure cultures of Shewanella putrefaciens J1-6-2-2 and A-4-3 and Shewanella xiamenensis DCB2-1 were capable of reducing nitrate ions to dinitrogen, which resulted in a decrease in the redox potential of the medium and contributed to reduction and deposition of pertechnetate, uranyl, and chromate ions. In the presence of organic substrates the strains formed biofilms on a number of natural materials (vermiculite, pearlite, schungite, etc.) with high sorption characteristics for cesium, strontium, uranium, and technetium. Analysis of the genome of strain DCB2-1 revealed a cluster of genes homologous to those determining biofilm formation in the well-known strain Shewanella oneidensis MR-1. The isolated strains may be used for introduction into subsurface horizons and enrichment of the natural microbial community in order to create a biogeochemical barrier for purification of groundwater from nitrate ions and immobilization of radioactive waste components.