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

Abstract

Kitasato Institute for Life Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, 108-8641, Japan A Gram-stain-negative, rod-shaped, motile bacterium, PC004 T , was isolated from root nodules of the Thai medicinal plant Pueraria candollei var. candollei. 16S rRNA gene sequence analysis indicated that the strain is phylogenetically related to species in the genus Rhizobium, showing highest similarity (96.6 %) with Rhizobium mesosinicum HAMBI 3194 T . The phylogenetic tree reconstructed based on 16S rRNA gene sequences showed that strain PC004 T forms a cluster with Rhizobium petrolearium KCTC 23288 T . Based on atpD, gyrB and recA gene sequences, strain PC004 T also showed low similarity (,90 %) to reference strains. These phylogenetic data indicate that PC004 T may represent a novel species. Strain PC004 T also exhibited low DNA-DNA relatedness with R. mesosinicum HAMBI 3194 T (8.2 %) and R. petrolearium KCTC 23288 T (26.3 %). The DNA G+C content of strain PC004 T was 64 mol%, which is within the range reported for the genus Rhizobium. The major fatty acid of PC004 T was C 18 : 1 v7c with minor amounts of C 16 : 0 , C 16 : 0 3-OH, C 18 : 0 3-OH, C 18 : 1 2-OH, C 19 : 0 cyclo v8c and summed feature 2. The strain was able to grow at pH 12 and with up to 2 % (w/v) NaCl. Strain PC004 T 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, strain PC004 T represents a novel species of the genus Rhizobium, for which the name Rhizobium puerariae sp. nov. is proposed; the type strain is PC004 T (5BCC 73740 T 5NBRC 110722 T ).

What makes rhizobia rhizosphere colonizers?

“…Furthermore, rhizobia are able to colonize the rhizosphere of a wide variety of plants, including nonlegumes. Recent studies have shown the presence of non-symbiotic rhizobia in the rhizosphere and within the root tissues of plants as different as Arabidopsis thaliana (Lundberg et al, 2012), palm tree (Yaish et al, 2016), sugar cane (de Souza et al, 2016) and even inside nodules formed by other rhizobia (Boonsnongcheep et al, 2016). For this reason, rhizobia are now considered part of the plant core microbiome (Yeoh et al, 2016).…”