Characterization of an Effective Salt-tolerant, Fast-growing Strain of Rhizobium japonicum

Abstract

Summary: Rhizobium japonicum USDA191 is a member of a new group of Rhizobium japonicum strains found in China. This strain is one of several strains shown to be salt-tolerant and fast-growing; it is unique in being the only strain of this group that effectively nodulates American soybean cultivars. For these reasons strain USDA191 was chosen for further study and comparison to the common American Rhizobium japonicum isolate USDA110. Strain USDA191 has a doubling time of 3.2 h in complex medium and grows in concentrations of up to 0.4 M-NaCl, while strain USDA110, which has a doubling time of 12 h, is severely inhibited in media containing 0.1 M-NaCl. Under salt stress conditions, intracellular levels of K+ and glutamate were shown to increase. A comparison based on carbohydrate metabolism, DNA homology and protein patterns on polyacrylamide gels reveals that strain USDA191 is more closely related to the fast-growing rhizobia than to Rhizobium japonicum. However, the strain retains capacity to nodulate American soybean and cowpea cultivars effectively.