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 06(T)) 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 11608(T), 99.0% to Brachybacterium conglomeratum DSM 10241 and 98.2% to Brachybacterium faecium DSM 4810(T). DNA-DNA hybridization with B. paraconglomeratum DSM 46341(T), B. conglomeratum DSM 10241(T), B. faecium DSM 4810(T), Brachybacterium tyrofermentans DSM 10673(T), Brachybacterium alimentarium DSM 10672(T), Brachybacterium fresconsis DSM 14564(T), Brachybacterium sacelli DSM 14566(T) and Brachybacterium muris DSM 15460(T) 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 06(T) 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-C(15:0) (52.07%); significant amounts of iso-C(16:0)(12.38%), iso-C(15:0 )(8.59%) and anteiso-C(17:0)(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 N(2) 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 06(T) should be placed in the genus Brachybacterium. Strain JG 06(T) represents a novel species of the genus Brachybacterium for which the name Brachybacterium saurashtrense sp. nov. is proposed (type strain JG 06(T)=DSM 23186(T)=IMCC 252(T)).