Three novel bacterial strains, designated Vu-144 T , 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-sporeforming, coccoid rods, and formed non-pigmented colonies. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain Vu-144 T was affiliated with an uncultivated lineage of the phylum Bacteroidetes. Its closest phylogenetic neighbour was the recently described species 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-C 15 : 0 , iso-C 17 : 0 3-OH and iso-C 15 : 1 G and minor amounts of summed feature 3 (C 16 : 1 v7c and/or iso-C 15 : 0 2-OH), C 16 : 0 and other fatty acids, allowing the differentiation of the strains from other genera. The G+C content of the genomic 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 genera. All three isolates showed plant-growth-promoting properties, e.g. the ability to produce indole-3-acetic acid and NH 3 and to solubilize phosphate, utilized 1-aminocyclopropane 1-carboxylate (ACC) as a sole source of nitrogen and possessed the ACC deaminase enzyme. The novel 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-144 T represents a novel genus and species in the family Chitinophagaceae, for which the name Arachidicoccus rhizosphaerae gen. nov., sp. nov. is proposed. The type strain of Arachidicoccus rhizosphaerae is Vu-144 T (5KCTC 22378 T 5NCIMB 14473 T). Abbreviations: ACC, 1-aminocyclopropane 1-carboxylate; IAA, indole-3acetic acid. The GenBank/EMBL/DDBJ accession numbers for the 16S rRNA gene sequences of strains Vu-144 T , Vu-35 and Vu-7 are EU672808, EU672809 and EU672810, respectively. Two supplementary tables and five supplementary figures are available with the online Supplementary Material.