Plasmid profiles of mercuric chloride tolerant rhizobia from horse gram (Macrotyloma uniflorum).

Thirty two rhizobia were isolated from the fresh healthy root nodules of horse gram. They were found to be highly salt tolerant. They were identified as rhizobia by cultural, biochemical and 16S rRNA sequence. The sequences of the four selected isolates were deposited in the NCBI GenBank. The obtained accession numbers were GQ483457, GQ483458, GQ483459 and GQ483460. All the rhizobia were able to grow at 10 ppm mercuric chloride concentration. Four isolates HGR-11, 16, 30 and 31 were used to study the effect of different concentrations of mercuric chloride on the growth of rhizobia. These isolates were able to grow at 30 ppm concentration also. In these isolates, HGR-11 and HGR-30 showed maximum growth at 20 ppm than at control. These isolates contained one mega plasmid (-22 kb) at 20 ppm mercuric chloride concentration.