Isolation and characterization of salt tolerant bacteria from saline soils of Bangladesh

Salinity is an important abiotic stress that limits the productivity of crops growing on the salt affected areas because excess salt concentration in the soil has detrimental effect on growth and development of plants. Beneficial microorganisms having the inimitable characteristics like tolerance to soil salinity, synthesis of plant growth hormones, facilitating nutrient uptake, bio-control ability and beneficial interaction with plants could be vital to address the problem. An experiment was carried out with the objectives of isolating and characterizing saline tolerant bacteria for utilizing as a tool for bioremediation. Soil samples were collected from three saline affected districts of Bangladesh viz. Khulna, Satkhira and Bhola. The highest bacterial population was found in Satkhira followed by Khulna and the lowest was found in Bhola. Eighteen (18) bacterial isolates viz. BU B1, BU B2, BU B3, BU B4, BU B5, BU B6, BU B7, BU B8, BU B9, BU S1, BU S2, BU S3, BU S4, BU S5, BU S6, BU S7, BU K1 and BU K2 were identified according to the colony color and shape. All the isolated bacteria showed positive response to produce IAA. Isolates BU S4, BU B7 and BU S1 showed highest IAA production ability. Among the 18 isolates, 12 were Gram positive and showed negative reaction on KOH test and the rest 6 isolates were Gram negative and showed positive reaction on KOH test. The isolates BU B1, BU B4, BU B6, BU S6, BU K1 and BU K2 were slow growing bacteria and the rest were fast grower. Biochemical tests indicate that 13 isolates were positive for catalase and P solubilization test. Whereas, 11 isolates could degrade the cellulose. For screening of bacterial isolates against NaCl tolerance, the isolates were cultured on NA medium having different salt concentrations. Experimental results reveal that all the isolates could tolerate 4.0% NaCl concentration except BU B6. Ten isolates showed the ability to tolerate NaCl up to 8.0%. The isolates BU B7 and BU S4 showed highest salinity tolerance along with better response to different biochemical characteristics. Therefore, these isolates may become promising for the bioremediation of soil salinity in the saline affected areas of Bangladesh.