Isolation and characterization of thermotolerant hydrocarbon degrading bacteria which sustained the activity at extreme salinity and high osmotic conditions.

The bioremediation method is considered an economical and environmentally friendly strategy for the remediation of oil-contaminated soils. However, some oil field areas have extreme environmental conditions that make it difficult to establish microbes for bioreme-diation. In this study, bacteria were isolated from oil-contaminated soils of the Dehloran oil fields, which have very harsh soil and weather conditions. Soil samples were collected from two highly contaminated mud pits. The petroleum content and physicochemical characteristics of the soil were investigated. Soil samples pollution were about 8%, sandy and alkaline, and their EC reached up to 125.6 ds/m in some samples. The isolated bacteria were screened according to their ability to grow on the M9 mineral medium containing crude oil as the sole carbon source. Moreover, their physiological characteristics in diesel degradation were investigated. The phenotypic, biochemical, and molecular characteristics of selected isolates and their stability under extreme conditions such as drought, salinity and high temperatures were investigated. Two isolates NC39 and NB391 showed the highest ability in diesel degradation. The results of 16SrRNA sequencing showed that NC39 isolate had 98% similarity to Pseudomonas sp. and isolate NB391 belonged to Pantoea agglomerans with 99% similarity. These two isolates showed a high ability to tolerate high salinity (10%), temperature (50°C), and drought (-0.73 MPa) stress. Exploiting these extremophile strains is a promising tool in the bioremediation of oil-contaminated soils in extreme environments.