Rhizobium puerariae sp. nov., an endophytic bacterium from the root nodules of the medicinal plant Pueraria candollei var. candollei

Abstract

A Gram negative, rod-shape, motile bacterium, PC004T, was isolated from root nodule of the Thai medicinal plant Pueraria candollei var. candollei. 16S rRNA gene sequences indicate that the strain is phylogenetically related to species in the genus Rhizobium, showing the highest similarity (96.6%) with Rhizobium mesosinicum HAMBI 3194T. The phylogenetic tree constructed using 16S rRNA gene sequences shows that strain PC004T forms a cluster with Rhizobium petrolearium KCTC 23288T. Based on atpD, gyrB and recA gene sequences, strain PC004T also shows low similarity (<90%) when comparing with reference strains. These phylogenetic data indicate that PC004T may represent a novel species. Strain PC004T also exhibits low DNA-DNA relatedness with R. mesosinicum HAMBI 3194T (8.2%) and R. petrolearium KCTC 23288T (26.3%). The DNA G+C content of strain PC004T is 64 mol%, which is in the range of genus Rhizobium. A major fatty acid of PC004T is C18:1 ω7c (75.1%) with minor amounts of C16:0 (3.9%), C16:0 3-OH (3.5%), C18:0 3-OH (2.2%), C18:1 2-OH (2.5%), C19:0 cyclo ω8c (3.0%) and summed feature 2 (5.4%). The strain can grow at pH 12 and up to 2% NaCl. Strain PC004T did not nodulate five tested legumes and the nifH and nodC genes were not detected by PCR. Based on the physiological, chemotaxonomic and phenotypic data from this study, the strain PC004T represents a novel species of genus Rhizobium, for which the name Rhizobium puerariae sp. nov. is proposed; the type strain is PC004T (BCC 73740T = NBRC 110722T).