Influence of salinity variations on exocellular polysaccharide production, biofilm formation and flocculation in halotolerant bacteria

Abstract

Aim: The present study was carried out to evaluate the exopolysaccharide (EPS) production, biofilm formation and flocculation in four halotolerant plant growth promoting (PGP) bacterial strains i.e., Brevibacterium iodinum RS16, Micrococcus yunnanensis RS222, Bacillus aryabhattai RS341, B. licheniformis RS656 underdifferentsaltlevels. Methodology: Four halotolerant plant growth promoting bacterial strains namely B. iodinum RS16, M. yunnanensis RS222, B. aryabhattai RS341 and B. licheniformis RS656 were studied for their exopolysaccharide (EPS) production, biofilm formation and flocculation efficiency under different NaCI levels. EPS production of halotolerant plant growth promoting strains was quantified in terms of dry weight and glucose content. Biofilm formation of the plant growth promoting halotolerant strains was quantified based on a micro titer plate assay. Plant growth-promoting efficiency of halotolerant strains was quantified in red pepper plants in terms ofvigor index and fresh weight. Results: Among the strains, strain B. aryabhattai RS341 recorded the highest EPS dry weight (5.80 gI-1), while the highest floe yield (0.60 g I-1 dry weight) was recorded by B. licheniformis RS656 at 2 mM NaCI concentration. Regression analysis revealed that EPS content, expressed in terms of dry weight, and flocculation in terms of floe yield, correlated positively with NaCI levels. The highest biofilm formation in Canola root surfaces was observed in the strain B. iodinum RS16 in all NaCI concentrations. All the halotolerant strains promoted plant growth as evidenced by the increased vigor index and fresh weight irrespective of the level of NaCI. Interpretation: It was observed that halotolerant bacterial strains were able to promote plant growth in the presence of NaCI through the mechanisms of EPS production, flocculation and biofilmformations.