The Correlation between Salt Tolerance and Extracellular Polysaccharide Production in Rhizobium.

Abstract

We examined the correlation between the extracellular polysaccharide (EPS) production and salt tolerance of rhizobia. Twelve rhizobial isolates from six different legume hosts were used in this study. Six isolates were found to be salt-tolerant to various degrees and other isolates were salt-sensitive in the presence of 0.5% or higher concentrations of NaCl in Mannitol-salt-yeast extract (MSY) culture broth. Salt-sensitive isolates developed dry and larger colonies on MSY agar plates, except TAL619 and CWP2 which developed larger and gummy colonies similar to the NaCl-tolerant isolates. Salt-sensitive isolates excreted lesser amounts of EPS even when they grew under stress-free conditions, except TAL619 and CWP2 which showed significant level of EPS production. On the other hand, salt-tolerant strains produced notable amounts of EPS. Among the six salt-tolerant isolates, RCSt1 and CPL3 showed sharp and significant rates of increase of EPS production with increasing salt concentration. Three other strains, RJL3, RMB3 and CWP2S showed less of an increase, while for TAL309L, the EPS production remained unaltered with increasing salt concentration. From the results, it appears that extracellular polysaccharide may have some influence on salt tolerance of certain rhizobial strains.