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 ZXT2-3T and ZXT2-6T, were isolated from the river sediment sample of Jinshui River in Xingtai City, Hebei Province, China. Based on 16S rRNA gene sequence analysis, strain ZXT2-3T showed the highest sequence similarity to Agromyces binzhouensis CGMCC 4.7180T (98.5%), and strain ZXT2-6T was most closely related to Agromyces arachidis JCM 19251T (99.1%), Agromyces indicus CCTCC AB 2011122T (98.8%), Agromyces aurantiacus DSM 14598T (98.6%), Agromyces tropicus JCM 15672T (98.4%), Agromyces mediolanus JCM 3346T (98.2%) and Agromyces soli JCM 16247T (98.0%). The 16S rRNA gene sequence similarity between strains ZXT2-3T and ZXT2-6T was 98.4%. Phylogenetic analysis based on 16S rRNA gene sequences and whole-genome sequences indicated that strains ZXT2-3T and ZXT2-6T belong to the genus Agromyces. The genome sizes of strains ZXT2-3T and ZXT2-6T 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 ZXT2-3T included anteiso-C15 : 0, iso-C16 : 0, anteiso-C17 : 0, C16 : 0 and iso-C15 : 0. For strain ZXT2-6T, the major cellular fatty acids were identified as anteiso-C15 : 0, anteiso-C15 : 1A, iso-C16 : 0 and anteiso-C17 : 0. The major respiratory quinones of strains ZXT2-3T and ZXT2-6T 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 ZXT2-3T was also capable of reducing Mo(VI) to molybdenum blue. According to the phenotypic, genotypic and phylogenetic data, strains ZXT2-3T and ZXT2-6T 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 ZXT2-3T (=GDMCC 1.4963T=JCM 37791T=MCCC 1K10748T) and ZXT2-6T (=GDMCC 1.4965T=JCM 37792T=MCCC 1K10749T), respectively.