Mucilaginibacter gossypii sp. nov. and Mucilaginibacter gossypiicola sp. nov., plant-growth-promoting bacteria isolated from cotton rhizosphere soils

Abstract

Two isolates from rhizosphere soil of cotton, designated Gh-67(T) and Gh-48(T), which produced large amounts of extracellular polysaccharide and possessed plant-growth-promoting traits, were characterized phenotypically and genotypically. The strains were Gram-negative and cells were non-motile rods that grew optimally at 28°C and grew between pH 4 and 7. 16S rRNA gene sequence analysis of strains Gh-67(T) and Gh-48(T) placed them in the genus Mucilaginibacter, with pairwise sequence similarity between them and type strains from related genera ranging from 93.9 to 98.2 %. The major fatty acids were iso-C₁₅:₀, C₁₆:₀ and summed feature 3 (C₁₆:₁ω7c and/or iso-C₁₅:₀ 2-OH). The strains contained MK-7 as the major isoprenoid quinone. The DNA G+C contents of strains Gh-67(T) and Gh-48(T) were 46.7 and 44.2 mol%, respectively. The low DNA-DNA hybridization value (18 %) and a number of phenotypic differences between strains Gh-48(T) and Gh-67(T) indicated that they represent two separate species. Results of phenotypic, phylogenetic and genotypic analysis revealed that the strains were separated from the species of Mucilaginibacter described to date. Therefore, strains Gh-67(T) and Gh-48(T) represent novel species of Mucilaginibacter, for which we propose the names Mucilaginibacter gossypii sp. nov. (type strain Gh-67(T) =NCIMB 14470(T) =KCTC 22380(T)) and Mucilaginibacter gossypiicola sp. nov. (type strain Gh-48(T) =NCIMB 14471(T) =KCTC 22379(T)).