Isolation and investigation of some growth-promoting properties of halotolerant bacteria -producing polymer of saline soils

Salinity is the most important challenge in arid and semi arid regions. Recently, biological methods are considered as a way for decreasing harmful effects of salinity on plant. In this study halotolerant bacteria were isolated from saline soils. The characteristics of plant growth promotion (PGP) such as production of exopolymer, siderophore, HCN, auxin, ability of potassium and phousphate solubilization and tolerance to drought stress were investigated. Among the 20 isolates selected, two isolates (5, 17) selected as super isolates based on PGP test. Results shown that mean produced exopolymer was in range of 0.8 to 4.2 g l-1 and maximum value was observed by the isolate17. All of the isolates can produce halo in CAS-Agar and bacteria isolate No. 5 produced maximum siderophore with the halo to colony ratio two. Maximum auxin production (8.14 mg l-1) was observed by the isolate17. Also, this isolate had highest ability of potassium solubilization in presence (12.20) and absence (18.62) of salt. Most of the isolates showed drought tolerance at 2 and 5 bar levels. At 15 bar, Isolates 17 and 5 has the highest tolerance to drought stress in comparison to control with 55.6 and 53.2 percentage reuction in growth rate, respectively. With 16S rRNA sequencing, the more closley studied of halotolerant superior isolates were identified as Bacillus. Isolate No. 17 had 99.4% similarity to Bacillus licheniformis DSM13, while isolate No.5 showed 99.57% sequence homology to Bacillus megaterium NBRC 15308.