Rhodoferax potami sp. nov. and Rhodoferax mekongensis sp. nov., isolated from the Mekong River in Thailand

Four newly discovered Gram-stain-negative bacteria, designated as BL00010 T , BL00058, D8-11 T and BL00200, were isolated from water samples collected at three hydrological monitoring stations (namely Chiang Saen, Chiang Khan and Nong Khai) located along the Mekong River in Thailand. An investigation encompassing phenotypic, chemotaxonomic and genomic traits was conducted. The results of phylogenetic analysis based on 16S rRNA gene sequences indicated that all four isolates represented members of the genus Rhodoferax . These isolates were closely related to Rhodoferax bucti KCTC 62564 T with a similarity of 99.59%. The major fatty acids of the four novel isolates included C 16:0 and C 16:1 ω7 c and/or C 16 : 1 ω6 c , whereas the major respiratory quinone was identified as ubiquinone Q-8. In addition, phosphatidylethanolamine was identified as a major polar lipid in these bacteria. The genomes of BL00010 T , BL00058, D8-11 T and BL00200 were similar in size (3.88–4.01 Mbp) and DNA G+C contents (59.5, 59.3, 59.5 and 59.3 mol%, respectively). In contrast to R. bucti KCTC 62564 T and Rhodoferax aquaticus KCTC 32394 T , the newly discovered species possessed several genes involved in nitrite and nitrile metabolism, which may be related to their unique adaptation to nitrile-rich environments. From the results of the pairwise analysis of average nucleotide identity of the whole genome and digital DNA–DNA hybridisation, it was evident that BL00010 T and D8-11 T represented two novel species, for which we propose the nomenclature Rhodoferax potami sp. nov., with the type strain BL00010 T (TBRC 17198 T = NBRC 116413 T ), and Rhodoferax mekongensis sp. nov., with the type strain D8-11 T (TBRC 17307 T = NBRC 116415 T ).