Arachidicoccus rhizosphaerae gen. nov., sp. nov., a plant-growth-promoting bacterium in the family Chitinophagaceae isolated from rhizosphere soil

Abstract

Three nov.l bacterial strains, designated Vu-144T, Vu-7 and Vu-35, were isolated on minimal medium from rhizosphere soil of field-grown cowpea and subjected to a taxonomic study using a polyphasic approach. Cells of the strains were Gram-stain-negative, non-motile, non-spore-forming, coccoid rods, and formed non-pigmented colonies. Phylogenetic analysis based on 16S rRNA gen. sequences revealed that strain Vu-144T was affiliated with an uncultivated lineage of the phylum Bacteroidetes. Its closest phylogenetic neighbour was the recently described sp.cies Niastella populi, a member of the family Chitinophagaceae, with just 90.7% sequence similarity to the type strain. The only isoprenoid quinone detected was menaquinone 7 (MK-7). The fatty acid profiles showed large amounts of iso-C15 : 0, iso-C17 : 0 3-OH and iso-C15 : 1 G and minor amounts of summed feature 3 (C16 : 1v7c and/or iso-C15: 0 2-OH), C16 : 0 and other fatty acids, allowing the differentiation of the strains from other gen.ra. The G+C content of the gen.mic DNA of the three strains ranged from 43.1 to 44.3 mol%. In addition to phosphatidylethanolamine, the major polar lipids were three unidentified aminophospholipids (APL1-APL3), two unidentified phospholipids (PL1, PL2) and three unidentified lipids (UL1-UL3). Biochemical test patterns also differed from those of Niastella populi and members of other gen.ra. All three isolates showed plant-growth-promoting properties, e.g. the ability to produce indole-3-acetic acid and NH3 and to solubilize phosphate, utilized 1-aminocyclopropane 1-carboxylate (ACC) as a sole source of nitrogen and possessed the ACC deaminase enzyme. The nov.l isolates readily colonized roots and stimulated growth of tomato and cowpea under glasshouse conditions. Inoculated plants showed a 45-60% increase in dry matter weight with respect to uninoculated controls. On the basis of the evidence from our polyphasic study, isolate Vu-144T represents a nov.l gen.s and sp.cies in the family Chitinophagaceae, for which the name Arachidicoccus rhizosphaerae gen. nov., sp. nov. is proposed. The type strain of Arachidicoccus rhizosphaerae is Vu-144T (5KCTC 22378T5NCIMB 14473T).