Brachybacterium saurashtrense sp. nov., a halotolerant root-associated bacterium with plant growth-promoting potential

Abstract

A Gram-positive-staining, aerobic, non-motile, coccoid shaped, halotolerant bacterium (strain JG 06T) was isolated from the roots of Salicornia brachiata, an extreme halophyte. Phylogenetic analysis based on 16S rRNA gene sequence showed that the novel strain had sequence similarities of 99.2 % to Brachybacterium paraconglomeratum JCM 11608T, 99.0 % to Brachybacterium conglomeratum DSM 10241 and 98.2 % to Brachybacterium faecium DSM 4810T. DNA–DNA hybridization with B. paraconglomeratum DSM 46341T, B. conglomeratum DSM 10241T, B. faecium DSM 4810T, Brachybacterium tyrofermentans DSM 10673T, Brachybacterium alimentarium DSM 10672T, Brachybacterium fresconsis DSM 14564T, Brachybacterium sacelli DSM 14566T and Brachybacterium muris DSM 15460T resulted in reassociation values of 36.2 %, 36.5 %, 35.8 %, 27.6 %, 27.9 %, 28.2 %, 28.7 % and 11.2 %, respectively. The peptidoglycan type of strain JG 06T was variant A4γ. The menaquinone content was MK7 (100 %). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, monogalactosyl diglyceride, three unidentified phospholipids and three glycolipids. The predominant fatty acid was anteiso-C15 : 0 (52.07 %); significant amounts of iso-C16 : 0 (12.38 %), iso-C15 : 0 (8.59 %) and anteiso-C17 : 0 (10.03 %) were also present. The G+C content of the DNA was 73.0 mol%. The strain formed a growth pellicle in nitrogen-free semisolid NFb medium containing NaCl at levels of up to 4 % (w/v) and reduced acetylene to ethylene, a result indicative of N2 fixation. In nutrient broth medium the novel strain grew at NaCl concentrations up to 15 % (w/v). It also had the ability to produce indole-3-acetic acid (IAA) and siderophores, utilized 1-aminocyclopropane-1-carboxylate (ACC) as a sole source of nitrogen and possessed the ACC deaminase enzyme. On the basis of physiological, biochemical data and phylogenetic analyses, strain JG 06T should be placed in the genus Brachybacterium. Strain JG 06T represents a novel species of the genus Brachybacterium for which the name Brachybacterium saurashtrense sp. nov. is proposed (type strain JG 06T = DSM 23186T = IMCC 252T).