Characterizing the new bacterial isolates of high yielding exopolysaccharides under hypersaline conditions

摘要

The ability of plant growth promoting bacteria (PGPR) to survive under salinity stress has important implications on the growth of their host plants. The production of different biochemicals by the bacteria including exopolysaccharides (EPS) may determine their survival as well as their alleviating effects under stress. However, one important approach, which deserves more attention, is the performance of PGPR under stressed conditions such as hypersaline conditions. Accordingly, the objectives of this study were: 1) the isolation and characterization of new bacterial isolates of high yielding EPS from a hypersaline soil, and 2) the investigation of EPS structure in the presence of salt. Samples of soil were spread on nutrient agar +/- %5 NaCl to determine the salt tolerant colonies with the maximum tolerable salt concentrations (MTC). Among the isolates of "salt tolerant bacteria" (STB), six isolates had the potential to produce EPS. According to 16S rDNA gene sequencing, three salt tolerant EPS-producing isolates were identified as Bacillus aerius ATHM35, Arthrobacter luteolus ATHM 36, and Halomonas eurihalina ATHM 37. It is the first time that Bacillus aerius and Arthrobacter luteolus have been isolated from hypersaline soils. The biochemical analyses indicated that the isolates were able to produce a wide range of products including enzymes such as urease, lactose, oxidase and catalase. With increasing salt concentration the production of EPS by the isolates significantly (P 0.05) increased. H. eurihalina showed the MTC of 25% and produced the highest amounts of EPS (0.277 gL(-1)) significantly higher than the other isolates. The FTIR spectrum of EPSs showed they are heteropolysaccharides containing the functional groups of hydroxyl, alkyne, amides and carboxyl, and the absorption peaks related to sugar units. These new salt-tolerant isolates of high yielding EPS are suitable biotechnological candidates for agricultural and environmental applications. (C) 2018 Elsevier Ltd. All rights reserved.