Steroidobacter flavus sp. nov., a microcystin-degrading Gammaproteobacterium isolated from soil.

A microcystin-degrading strain, designated CPCC 100154(T), was isolated from a forest soil sample collected from Hainan Island, South China. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain CPCC 100154(T) is affiliated to the family Sinobacteraceae in Gammaproteobacteria, with high 16S rRNA gene sequence similarities of 98.1, 96.6 and 96.6 % to Steroidobacter agariperforans JCM 18477(T), S. denitrificansis DSM 18526(T), and Povalibacter uvarum JCM 18749(T), respectively. In the phylogenetic tree based on 16S rRNA gene sequences, strain CPCC 100154(T) formed a stable phylogenetic subclade with S. agariperforans JCM 18477(T), which indicated that strain CPCC 100154(T) should be identified as a member of the genus Steroidobacter. The phylogenetic analysis based on partial gyrB gene sequences confirmed the affiliation of strain CPCC 100154(T) to the genus Steroidobacter. While the DNA-DNA hybridization value (47.0 ± 1.7 %) between the new isolate and its near phylogenetic neighbor S. agariperforans JCM 18477(T) was far below 70 %, which demonstrated that strain CPCC 100154(T) represents a different genomic species from S. agariperforans. The strain CPCC 100154(T) was found to be a Gram-stain negative, rod-shaped, motile with a polar flagellum, non-endospore-forming bacterium. Good growth was observed at 28-32 °C and pH 7.0-7.5. Polar lipids were identified to be diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, a unidentified phospholipid, an aminophospholipid and an unidentified aminolipid. The polyamine pattern was determined to contain spermidine as the predominant polyamine, moderate amounts of putrescine as well as traces of sym-homospermidine and spermine. The respiratory quinone was identified as ubiquinone-8. The major cellular fatty acids were found to include summed feature 3 (C16: 1 ω7C/C16: 1 ω6C) (46.1 %) and C16: 0 (29.6 %). The genomic DNA G+C content was determined to be 64.4 mol%. On the basis of the above polyphasic taxonomy evidence, a novel species, Steroidobacter flavus sp. nov. is proposed. The type strain is CPCC 100154(T) (=DSM 23339(T) =CGMCC 1.10759(T)).