Ornithinimicrobium tianjinense sp. nov., isolated from a recirculating aquaculture system

A Gram-positive, strictly aerobic and heterotrophic, non-spore-forming actinobacterium (strain B2^T) isolated from a recirculating aquaculture system was studied for its taxonomic position. Strain B2^T formed a rudimentary substrate-mycelium that fragmented into short rod-shaped to coccoid cells (0.5 µm×0.5–2.2 µm or 0.5–1.0 µm in diameter). Colonies were yellow, smooth, circular and 1.5–2.0 mm in diameter after incubation on TSA for 3 days at 30 °C. Strain B2^T grew at 20–40 °C (optimal, 30 °C) and pH 5.5–9.5 (optimal, 6.5–7.0) and in the presence of 0–9 % (w/v) NaCl (optimal, 1 %). The predominant menaquinone of strain B2^T was MK-8(H₄). The cell-wall peptidoglycan of strain B2^T contained the amino acids ornithine, glutamic acid, alanine, glycine and aspartic acid. The major polar lipids were phosphatidylglycerol and diphosphatidylglycerol. The major fatty acids were iso-C_15 : 0, iso-C_16 : 0 and summed feature 9. Its DNA G+C content was 68.3 mol% (T_m). Analysis of 16S rRNA gene sequences indicated that strain B2^T was related phylogenetically to members of the genus Ornithinimicrobium with highest similarity (96.6 %) to Ornithinimicrobium kibberense DSM 17687^T, followed by Ornithinimicrobium humiphilum DSM 12362^T (96.3 %), Ornithinimicrobium pekingense LW6^T (96.2 %) and Ornithinimicrobium murale 01-Gi-040^T (94.8 %). On basis of phenotypic, chemotaxonomic and phylogenetic data, it was concluded that strain B2^T represents a novel species of the genus Ornithinimicrobium, for which the name Ornithinimicrobium tianjinense sp. nov. is proposed. The type strain is B2^T ( = CGMCC 1.12160^T = JCM 18464^T).