Genomic Analysis of Actinotalea Species, Description of Actinotalea alkalitolerans sp. nov. from an Alkaline Radioactive Waste Repository, and Proposals on Actinotalea Taxonomy

Abstaract The storage of alkaline liquid radioactive waste (LRW) in surface reservoirs leads to stimulation of a number of microbial processes that should be taken into account in the case of long-term storage. The microorganisms of alkaline LRW have been poorly studied. The purpose of this work was to isolate bacteria from an LRW sample with pH of 10.5 and to determine their possible participation in the transformation of waste components. The K2T strain isolated from the LRW sample was alkalitolerant, resistant to increased gamma radiation level and heavy metal content, and was able to sorb and reduce uranium(VI) and technetium (VII). The strain was investigated using the polyphase taxonomy and genomic approaches. Average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) values of the K2T genome with the genomes of type strains of the genus Actinotalea ranged from 78.8 to 81.1 and from 19.2 to 20.8%, respectively, and were below the species delineation thresholds. The genetic determinants identified in the genome of strain K2T were responsible for replication and repair processes, maintaining the genome stability, reduction of nitrate to nitrite, alkaliphily, heavy metal resistance, and carbohydrate utilization. Based on physiological, chemotaxonomic, and genomic studies, strain K2T was assigned to a novel species within the genus Actinotalea, for which the name Actinotalea alkalitolerans sp. nov. is proposed. These results show that microorganisms inhabiting alkaline waste can participate in conversion of radioactive and non-radioactive components of LRW. Taxonomy of bacteria of the genus Actinotalea is also discussed.