A salt resistant biosurfactant produced by moderately halotolerant Pseudomonas aeruginosa (AHV-KH10) and its application for bioremediation of diesel-contaminated sediment in saline environment

A halotolerant bacterial strain was isolated from oily-contaminated sites of Persian Gulf, which characterized as Pseudomonas aeruginosa (AHV-KH10) by 16S rRNA gene sequencing. This strain was used for bioremediation of diesel-contaminated sediments. Biosurfactant production was initially screened by using oil displacement test and drop-collapse method, followed by measurement of surface tension (ST) of growth medium. Produced biosurfactant was a rhamnolipid type biosurfactant and lowered the ST to 33.4 mN/m at the given critical micelle concentration (CMC) of 75 mg/L. Addition of 3 CMC rhamnolipid, inoculums size of 15 mL, biodegradation in slurry phase and salinity level of 6% led totally to a diesel biodegradation rate of 70% for initial concentration of 1000 mg/kg after 35 days. The maximum diesel removal occurred at the salinity content of 6% indicating the moderately halo-tolerant characteristics of isolated strain. Evaluation of bacterial growth showed a biomass yield of 0.33 mg (VSS)/mg (diesel) in selected conditions. The field performance of Pseudomonas aeruginosa AHV-KH10 was proved through the removal of the TPH content in unwashed sediment, which varied from 2390 to 1875 mg/kg within four months.