Zoogloea oryzae sp. nov., a nitrogen-fixing bacterium isolated from rice paddy soil, and reclassification of the strain ATCC 19623 as Crabtreella saccharophila gen. nov., sp. nov.

Two strains of free-living diazotrophs isolated from soil from a rice paddy field were characterized by using a polyphasic approach. The novel strains, A-7T and A-4, were found to be very closely related, with 99.9% 16S rRNA gene sequence similarity and a DNA-DNA hybridization value of 89.5%, suggesting that they represent a single species. 16S rRNA gene sequence analyses indicated that the two strains fell within the Zoogloea lineage, with less than 96.7 % sequence similarity to other Zoogloea species. Chemotaxonomic characteristics of the novel strains, including DNA G + C content (65.1 mol%), the major quinone system (Q-8), predominant fatty acids (16:1omega7c and 16:0) and major hydroxy fatty acids (3-OH 10:0 and 3-OH 12:0), are similar to those of the genus Zoogloea. The novel strains showed positive results for floc formation which is accepted as confirmatory for species of the genus Zoogloea. However, the novel strains can be distinguished from the other species of Zoogloea by physiological characteristics. The name Zoogloea oryzae sp. nov. is therefore proposed for the novel strains with strain A-7T (= IAM 15218T = CCTCC AB 2052005T) as the type strain. Phylogenetic and chemotaxonomic analyses indicate that strain ATCC 19623, designated as a reference strain of Zoogloea ramigera, does not belong to the genus Zoogloea but to a new genus of Alphaproteobacteria. The name Crabtreella saccharophila gen. nov., sp. nov. is proposed for strain ATCC 19623T (= IAM 12669T).