Screening of biosurfactant producing bacteria from diesel-contaminated soils in Kerman, Iran

BACKGROUND AND OBJECTIVESBiosurfactants are microbial compounds that exhibit emulsifying activities. These amphipathic molecules have variety applications in biotechnology such as biodegradation and detoxification of industrial effluents, bioremediation and enhanced oil recovery due to their emulsification, cleansing, surface activity. Biosurfactants have also shown their antimicrobial and antibiofilm properties in red Biotechnology. Accordingly, the aim of this research was to isolate biosurfactant producing bacteria and their products from diesel-contaminated soils.MATERIALS AND METHODSTen grams of diesel contaminated soil was cultivated in ۹۰ ml of Bushnell-Haas broth containing ۲% diesel fuel as the carbon source and aerated at ۱۵۰ rpm in shaker incubator for ۳ days adjusted on ۳۰oC. Serial diluted grown cultures were inoculated on nutrient agar plates by spreading method and incubated at ۳۰oC during ۲۴ hours to achieve pure cultures. Primary tests such as hemolytic activity, emulsification, drop collapse assay, oil spreading and biochemical activities were evaluated about each isolate. Three selected isolates were cultivated in broth at ۳۰oC and ۱۵۰ rpm. After ۱۰ days, grown cultures were centrifuged for ۱۵ min at ۸۰۰۰ rpm. Cell-free supernatant was adjusted to pH: ۲ with ۶M HCl and stored overnight at ۴°C. Precipitated biosurfactants recovered using methanol and chloroform (۱:۲ v/v). Hydrophobic phase was separated using funnel and dried at ۵۰oC to obtain dry mass.RESULTS AND DISCUSSIONFifteen Gram-negative and three Gram-positive bacteria were isolated. They were monitored without hemolytic activity, beta and alpha hemolysis as ۶۳.۱۵%, ۲۱.۰۷% and ۱۵.۷۸%, respectively. Oil Spreading revealed a range between ۳-۱۲ mm. Out of ۱۹ isolates ۳ ones showed best results related to the primary tests. The best emulsifier isolate as IAUK۱۰۱ was able to produce ۹.۱۵ grams of dry biosurfactant from ۵۰۰ ml broth medium.CONCLUSIONThree selected isolates had emulsion more than ۵۰% and showed high efficiencies in biosurfactant production. These biosurfactants have a good potential to be use in bioremediation of hydrocarbons contaminated environments and further related biotechnological purposes.

کلیدواژه ها:

Biosurfactant ، Diesel-contaminated soils ، Emulsification ، bioremediation