Effect of biofilm forming plant growth promoting rhizobacteria on salinity tolerance in barley

Formation of biofilm under varying stress conditions is a significant strategy adopted by bacterial strains for their successful survival in plant rhizosphere. In this study, the activity of biofilm formation of 20 isolates and strains of plant growth promoting rhizobacteria (PGPR) was determined under different salt concentrations. The results indicated that all of the 20 PGPRs have the activity of biofilm formation under 0.0, 250, 500 or 1000 mM NaCl which was increased with increasing salt concentration. PGPR strains with the highest activity of biofilm formation were selected and used to coat barley grains. The coated grains were sown in clay/sandy soil and left to grow for 25 days. The results showed that bacterial inoculation was effective in alleviating the deleterious effect of salinity on some growth criteria (seedling length, fresh and dry masses as well as relative water content), compared with the control. The isolate HM6 (B6), which showed the highest activity of biofilm formation at all the studied NaCl concentrations, was identified using 16S ribosomal RNA gene amplification and sequencing of the PCR product. The similarity sequence analysis indicated that HM6 isolate has 97.4% similar sequence identity to Bacillus amyloliquifaciens. It could be speculated that the bacterial activity of biofilm formation is helpful for improving salt stress tolerance of barley.