A novel aerobic, non-motile, pleomorphic, Gram-negative and nitrogen-fixing bacterial strain, designated R5-392T, was isolated from surface-sterilized root tissue of Jatropha curcas. The organism grew optimally at 30 °C in media containing 1 % (w/v) NaCl and at pH 6.0–8.0. The predominant ubiquinone was Q-10 and the major fatty acids were C18 : 1ω7c/C18 : 1ω6c, C16 : 0 and C19 : 0 cyclo ω8c. The DNA G+C content was 63.2 mol%. Analysis of the 16S rRNA gene sequence suggested that strain R5-392T is affiliated with the order Rhizobiales within the class Alphaproteobacteria and is most closely related to Pleomorphomonas oryzae F-7T (98.8 % similarity) and Pleomorphomonas koreensis Y9T (98.3 % similarity). Analysis of partial nifH gene sequences also revealed a monophyletic lineage within the class Alphaproteobacteria , and strain R5-392T was most closely related to P. oryzae F-7T (98 %). Highest nitrogenase activity was detected in the presence of low-level organic nitrogen or in the presence of nitrogenase co-factors (Fe/Mo) in N-free media. Phenotypic and chemotaxonomic data suggest that strain R5-392T represents a novel species within the genus Pleomorphomonas , for which the name Pleomorphomonas diazotrophica sp. nov. is proposed. The type strain is R5-392T ( = KACC 16233T = DSM 25022T).