Characterization of exopolymeric substances from selected Rhodopseudomonas palustris strains and their ability to adsorb sodium ions

•Rhodopseudomonas palustris secreted exopolymeric substances (EPS) to resist NaCl.•The maximum EPS production by R. palustris PP803 and TN114 was found at 1% NaCl.•EPS from strain PP803 had higher efficiency to remove Na+ than EPS from TN114.•The main part of EPS from strain PP803 that binds with Na+ was galacturonic acid. Removal of Na+ by binding with exopolymeric substances (EPS) from Rhodopseudomonas palustris TN114 and PP803 was investigated. The moderate negative correlation pairs (rp) between remaining Alcian blue and amount of Na+ adsorbed on EPS from strains TN114 and PP803 were −0.652 and −0.609. Both strains showed positive relationships between the amounts of EPS produced and bacterial growth. EPS from strain PP803 had a higher efficiency in removing Na+ than the EPS from strain TN114 based on their EC50 values (1.79 and 1.49mg/mL for TN114 and PP803, respectively). The principal component from EPS of strain PP803 which was responsible for salt removal was purified and it was identified as a polysaccharide (≈18kDa) mainly composed of galacturonic acid. Overall results suggested that EPS is a key factor that our strains used to bind Na+ allowing their survival in high NaCl concentrations.