Magnetospirillum caucaseum sp. nov., Magnetospirillum marisnigri sp. nov. and Magnetospirillum moscoviense sp. nov., freshwater magnetotactic bacteria isolated from three distinct geographical locations in European Russia.

Three strains of helical, magnetotactic bacteria, SO-1T, SP-1T and BB-1T, were isolated from freshwater sediments collected from three distinct locations in European Russia. Phylogenetic analysis showed that the strains belong to the genus Magnetospirillum. Strains SO-1T and SP-1T showed the highest 16S rRNA gene sequence similarity to Magnetospirillum magnetotacticum MS-1T (99.3 and 98.1 %, respectively), and strain BB-1T with Magnetospirillum gryphiswaldense MSR-1T (97.3 %). The tree based on concatenated deduced amino acid sequences of the MamA, B, K, M, O, P, Q and T proteins, which are involved in magnetosome formation, was congruent with the tree based on 16S rRNA gene sequences. The genomic DNA G+C contents of strains SO-1T, SP-1T and BB-1T were 65.9, 63.0 and 65.2 mol%, respectively. As major fatty acids, C18 : 1ω9, C16 : 1ω7c, C16 : 0 and C18 : 0 were detected. DNA–DNA hybridization values between the novel strains and their closest relatives in the genus Magnetospirillum were less than 51.7 ± 2.3 %. In contrast to M. magnetotacticum MS-1T, the strains could utilize butyrate and propionate; strains SO-1T and BB-1T could also utilize glycerol. Strain SP-1T showed strictly microaerophilic growth, whereas strains SO-1T and BB-1T were more tolerant of oxygen. The results of DNA–DNA hybridization and physiological tests allowed genotypic and phenotypic differentiation of the strains from each other as well as from the two species of Magnetospirillum with validly published names. Therefore, the strains represent novel species, for which we propose the names Magnetospirillum caucaseum sp. nov. (type strain SO-1T = DSM 28995T = VKM B-2936T), Magnetospirillum marisnigri sp. nov. (type strain SP-1T = DSM 29006T = VKM B-2938T) and Magnetospirillum moscoviense sp. nov. (type strain BB-1T = DSM 29455T = VKM B-2939T).