Agromyces molybdatiresistens sp. nov. and Agromyces selenitireducens sp. nov., two molybdate/selenite co-resistant and reducing bacteria isolated from riverbed silt

Two actinobacterial strains with resistance to selenite and molybdate, designated as ZXT2-3 ^T and ZXT2-6 ^T , were isolated from the river sediment sample of Jinshui River in Xingtai City, Hebei Province, China. Based on 16S rRNA gene sequence analysis, strain ZXT2-3 ^T showed the highest sequence similarity to Agromyces binzhouensis CGMCC 4.7180 ^T (98.5%), and strain ZXT2-6 ^T was most closely related to Agromyces arachidis JCM 19251 ^T (99.1%), Agromyces indicus CCTCC AB 2011122 ^T (98.8%), Agromyces aurantiacus DSM 14598 ^T (98.6%), Agromyces tropicus JCM 15672 ^T (98.4%), Agromyces mediolanus JCM 3346 ^T (98.2%) and Agromyces soli JCM 16247 ^T (98.0%). The 16S rRNA gene sequence similarity between strains ZXT2-3 ^T and ZXT2-6 ^T was 98.4%. Phylogenetic analysis based on 16S rRNA gene sequences and whole-genome sequences indicated that strains ZXT2-3 ^T and ZXT2-6 ^T belong to the genus Agromyces . The genome sizes of strains ZXT2-3 ^T and ZXT2-6 ^T were 3.9 and 4.0 Mb, with DNA G+C contents of 72 and 71.5 %, respectively. The average nucleotide identity and digital DNA–DNA hybridization values with the closest relatives were below species delineation thresholds. The major fatty acids detected in strain ZXT2-3 ^T included anteiso-C _{15 : 0} , iso-C _{16 : 0} , anteiso-C _{17 : 0} , C _{16 : 0} and iso-C _{15 : 0} . For strain ZXT2-6 ^T , the major cellular fatty acids were identified as anteiso-C _{15 : 0} , anteiso-C _{15 : 1} A, iso-C _{16 : 0} and anteiso-C _{17 : 0} . The major respiratory quinones of strains ZXT2-3 ^T and ZXT2-6 ^T were MK-11 and MK-12. The polar lipid profiles of both strains contained diphosphatidylglycerol, phosphatidylglycerol and unidentified glycolipids. Both isolates could reduce Se(IV) to produce selenium-containing particles. Strain ZXT2-3 ^T was also capable of reducing Mo(VI) to molybdenum blue. According to the phenotypic, genotypic and phylogenetic data, strains ZXT2-3 ^T and ZXT2-6 ^T represent two novel species of the genus Agromyces , for which Agromyces molybdatiresistens sp. nov. and Agromyces selenitireducens sp. nov. are proposed, respectively. The type strains are ZXT2-3 ^T (=GDMCC 1.4963 ^T =JCM 37791 ^T =MCCC 1K10748 ^T ) and ZXT2-6 ^T (=GDMCC 1.4965 ^T =JCM 37792 ^T =MCCC 1K10749 ^T ), respectively.