Gracilibacillus boraciitolerans sp. nov., a highly boron-tolerant and moderately halotolerant bacterium isolated from soil

Abstract

A motile, Gram-positive, boron-tolerant and moderately halotolerant rod-shaped bacterium was isolated from a soil naturally high in boron minerals found in the Hisarcik area of Turkey. The novel isolate, designated T-16XT, produced spherical or ellipsoidal endospores in a non-bulging or slightly swollen sporangium in a terminal position and survived in a medium containing up to 450 mM boron. Whereas it tolerated 11 % (w/v) NaCl, it also grew without NaCl or boron. The temperature range for growth was 16–37 °C (optimum 25–28 °C) and the pH range for growth was 6.0–10.0 (optimum pH 7.5–8.5). The DNA G+C content was 35.8 mol% and the major cellular fatty acids were iso-C15 : 0and anteiso-C15 : 0at 18.2 and 45.7 % of the total fatty acids, respectively. MK-7 (90 %) was the predominant respiratory quinone system andmeso-diaminopimelic acid was the predominant diamino acid of the cell-wall peptidoglycan. Phylogenetic analysis of the 16S rRNA gene sequence revealed that the novel strain is closely related to the type strains ofGracilibacillus orientalis(96.7 % similarity),G. halotolerans(95.5 %) andG. dipsosauri(95.4 %). However, the maximum DNA hybridization value for this strain with these closely related strains was less than 26.2 %. On the basis of 16S rRNA gene sequence data and chemotaxonomic and physiological features, the organism T-16XT(=DSM 17256T=IAM 15263T=ATCC BAA-1190T) is proposed to be a member of the genusGracilibacillusas the type strain of the novel speciesGracilibacillus boraciitoleranssp. nov.