Rhizobium populi sp nov., an endophytic bacterium isolated from Populus euphratica

An endophytic bacterium, designated K-38(T), was isolated from the storage liquid in the stems of Populus euphratica trees at the ancient Ugan River in Xinjiang, PR China. Strain K-38(T) was found to be rod-shaped, Gram-stain-negative, aerobic, non-motile and non-spore-forming. Strain K-38(T) grew at temperatures of 25-37 degrees C (optimum, 28 degrees C), at pH 6.0-9.0 (optimum, pH 7.5) and in the presence of 0-3% (w/v) NaCl with 1% as the optimum concentration for growth. According to phylogenetic analysis based on 16S rRNA gene sequences, strain K-38(T) was assigned to the genus Rhizobium with highest 16S rRNA gene sequence similarity of 97.2% to Rhizobium rosettiformans W3(T), followed by Rhizobium nepotum 39/7(T) (96.5 %) and Rhizobium borbori DN316(T) (96.2%). Phylogenetic analysis of strain K-38(T) based on the protein coding genes recA, atpD and nifH confirmed (similarities were less than 90%) it to be a representative of a distinctly delineated species of the genus Rhizobium. The DNA G+C content was determined to be 63.5 mol%. DNA-DNA relatedness between K-38(T) and R. rosettiformans W3(T) was 48.4%, indicating genetic separation of strain K-38(T) from the latter strain. The major components of the cellular fatty acids in strain K-38(T) were revealed to be summed feature 8 (comprising C-18:1 omega 7c and/or C-18:1 omega 6c; 57.2%), C-16:0 (13.6%) and summed feature 2 (comprising C-12:0 aldehyde, C-14:0 3-OH/ISO-C-16:1 I and/or unknown ECL 10.928; 11.0%). Polar lipids of strain K-38(T) include phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, two unidentified aminophospholipids and two unidentified phospholipids. Q-10 was the major quinone in strain K-38(T). Based on phenotypic, chemotaxonomic and phylogenetic properties, strain K-38(T) represents a novel species of the genus Rhizobium, for which the name Rhizobium populi sp. nov. is proposed. The type strain is K-38(T) (=CCTCC AB 2013068(T)=NRRL B-59990(T)=JCM 19159(T)).