Aquibium microcysteis gen. nov., sp. nov., isolated from a Microcystis aeruginosa culture and reclassification of Mesorhizobium carbonis as Aquibium carbonis comb. nov. and Mesorhizobium oceanicum as Aquibium oceanicum comb. nov

A novel bacterial strain, NIBR3(T), was isolated from a Microcystis aeruginosa culture. Strain NIBR3(T) was characterized as Gram-negative, rod-shaped, catalase- and oxidase-positive, and aerobic. The 16S rRNA gene sequence analysis showed that strain NIBR3(T) was most closely related to Mesorhizobium carbonis B2.3(T) (=KCTC 52461), Mesorhizobium oceanicum B7(T) (=KCTC 42783) and Mesorhizobium qingshengii CCBAU 33460(T) (=HAMBI 3277), at 98.7, 97.2 and 97.2% similarity, respectively. Our phylogenetic analyses revealed that three strains [strain NIBR3(T) with the previously reported two Mesorhizobium species (M. carbonis B2.3(T) and M. oceanicum B7(T))] formed a distinct cluster from other Mesorhizobium type strains. The average nucleotide identity of strain NIBR3(T) relative to M. carbonis B2.3(T), M. oceanicum B7(T), and M. qingshengii CCBAU 33460(T) was found to be 84.3, 79.4 and 75.8%, with average amino-acid identities of 85.1, 74.8 and 64.3%, and digital DNA-DNA hybridization values of 27.6, 22.6 and 20.7%, respectively. The genome size and genomic DNA G+C content of NIBR3(T) were 6.1 Mbp and 67.9 mol%, respectively. Growth of strain NIBR3(T) was observed at 23-45 degrees C (optimum, 33 degrees C), at pH 6-11 (optimum, 8) and in the presence of 0-4% (w/v) NaCl (optimum, 0%). The major polar lipids in this novel strain were phosphatidylethanolamine, phosphatidylcholine and phosphatidylmethylethanolamine. The predominant respiratory quinone was Q-10. Summed feature 8 (C-18:1 omega 7c and/or C-18:1 omega 6c) was the most abundant cellular fatty acid in strain NIBR3(T). Based on genotypic characteristics using our genomic data, strain NIBR3(T) was identified as a member of new genus, Aquibium gen. nov., with the two aforementioned stains. The type strain f the novel species, Aquibium microcysteis sp. nov., is NIBR3(T) (=KACC 22092(T)=HAMBI 3738(T)). We also reclassified Mesorhizobium carbonis and M. oceanicum as Aquibium carbonis comb. nov. and A. oceanicum comb. nov., respectively.

Automated summary

A novel bacterial strain, NIBR3(T), isolated from a Microcystis aeruginosa culture, was identified as a member of a new genus, Aquibium gen. nov. The type strain of the new species, Aquibium microcysteis sp. nov., is NIBR3(T).