ИСТИНА

The goal of the study was to investigate the microbial community in the groundwater with high nitrate concentration of a suspended surface repositories for liquid radioactive waste and sludges (Siberia, Russia) and to determine the possibility of in situ groundwater bioremediation by removal of nitrate ions. Groundwater in the liquid radioactive waste repository area (10-m depth) had elevated concentrations of strontium, nitrate (up to 5000 mg/l), sulfate, and bicarbonate ions with neutral pH levels. Water samples collected nearby uranium sludges repository had high nitrate (up to 15000 mg/l), sulfate, and uranium concentrations and with alkaline pH levels (8-9,5). High-throughput sequencing of the V3-V4 region of the 16S rRNA gene revealed the presence of members of the phyla Proteobacteria (genera Alicycliphilus, Thermomonas, Herminiimonas Pseudomonas, Brevundimonas), Firmicutes (genera Bacillus and Paenibacillus), and Actinobacteria (Candidatus Planktophila). Groundwater samples contained culturable aerobic organotrophic, as well as anaerobic fermenting, iron-reducing, and denitrifying bacteria. Members of the genera Pseudomonas, Rhizobium, Cupriavidus, Shewanella, Ensifer, and Thermomonas reduced nitrate to nitrite and/or dinitrogen. Application of specific primers revealed the nirS and nirK genes encoding nitrite reductases in bacteria of the genera Pseudomonas, Rhizobium, and Ensifer. Among the organic substrates tested, sodium acetate and milk whey were the best for stimulation of denitrification by the microcosms with groundwater microorganisms. Injection of these substrates into the subterranean horizon (single-well push-pull test) resulted in temporary removal of nitrate ions in the area of the suspended radioactive waste repository and confirmed the possibility for in situ application of this method for bioremediation. In water samples collected nearby sludge repository (with high nitrate concentrations and pH levels 9-9,5) we found aerobic organotrophic, iron-reducing, sulphate reducing and denitrifying bacteria. Dominating genera where Pseudomonas, Lysobacter, Alidiomarina, Sporosarcina, Hermiimonas, Parapusilimonas, Pusillimonas, Nitrosospira.