Isolation, Molecular Identification, and Assessing Plant Growth Promoting Activities of Biofilm Forming Bacteria from Gramineae Rhizosphere in North West of Iran

Plant-associated rhizospheric bacteria which form biofilms have higher positive effects on plants in fluctuating environments. Thus, to study of these bacteria, 50 rhizospheric samples were taken from grass geramineae roots. After preparing the suspension, 100 microlitere was cultured on TSA medium and then pure culture of bacteria was prepared. Resulted showed that up to 90% of these isolates were able to form biofilm, so that they could be categorized in five groups as: pellicle, very adherent, moderately adherent, weakly adherent and non-adherent. 16S rDNA analysis revealed six different genus of bacteria. Bacillus are the predominant group (80%) of robust biofilm forming in the grass geramineae rhizosphere. The water deficit tolerance of isolates was assessed by rising concentration of sorbitol (1, 10, 20 and 30 %, w/v). All isolates were able to grow in -25 bar matric potential. Isolates showed good potential to producing auxins ranging from 6 - 65 µg mL-1, ACC-deaminase activity (up to 2.14 µmol α-ketobutyrate in 36 h), Ca3(PO4)2 solublization ranging from 1.2 – 251 mg L-1 and K releasing ability 90 to 250 mg L-1. Only three bacteria were able to produce siderophore. It seems that these isolates can be suitable candidates for doing some greeanhaous or pot experiment subjected to protecting plants against water deficit stress. Moreover, they can act as plant growth promoting bacteria as well.