Salt tolerance characteristics of rhizobium species associated with Vigna marina

Abstract

A study was conducted during 2003–04 to examine the characteristics of rhizobia associated with Vigna marina (Burm.) Merr. (syn. V. retusa. Walp) a wild legume of Andaman and Nicobar islands, which was found growing naturally in the sandy seashore and was able to survive high saline environment with prolific root nodules. The rhizobia associated with the root nodule of V. marina was collected, characterized and studied for their growth and salt tolerance properties. The plant gave more root/shoot ratio (0.76) and had runner type roots with more than 50% viable nodules. Salinity however did not hinder the nodulation process. The Rhizobium was found to be tolerant to antibiotics, like erythromycin, chloromphenicol, streptomycin and ampicillin. High membrane protein (14.98 μg/ml) was observed in the cells of Rhizobium VM1 indicating lesser degradation of protein under saline environment. Lipopolysaccharide profile revealed that the bacterium was closely related to Rhizobium of cowpea (Vigna unguiculata (L.) Walp) and blackgram (Vigna mungo (L.) Hepper). The bacteria showed resistance up to 600 mM NaCl and tolerance up to 1000 mM of NaCl in vitro.