Isolation and characterization of biosurfactant-producing and diesel oil degrading Pseudomonas sp. CQ2 from Changqing oil field, China

Abstract

In the present research investigation, 13 indigenous bacteria (from CQ1 to CQ13) were isolated from soil collected from Changqing oil field of Xi'an, China. Four promising biosurfactant producers (CQ1, CQ2, CQ4, and CQ13) were selected through primary screening among these 13 strains, including via drop collapse and oil-spreading methods. However, only the strain CQ2 showed the best biosurfactant production and was further screened by hemolytic assay, cetyl trimethyl ammonium bromide (CTAB), surface tension and emulsifying activity. The bacterium CQ2 has the ability to produce about 3.015 g L⁻¹ of biosurfactant using glucose as the sole carbon source without any optimization. The produced biosurfactant could greatly reduce surface tension from 72.66 to 24.72 mN m⁻¹ with a critical micelle concentration (CMC) of 30 mg L⁻¹ and emulsify diesel oil up to 60.1%. The cell-free broth was found to be stable in wide temperature (4–100 °C), pH (6–12) and salinity (2–20%) ranges for surface and emulsifying activity. This biosurfactant was preliminarily found to be of a glycolipid nature as evident from thin-layer chromatographic (TLC) and Fourier transform infra-red spectroscopic (FTIR) analyses. Moreover, CQ2 was able to degrade 54.7% of diesel oil, which surprisingly could form a substantial amount of bioflocculants during the degradation process. Furthermore, the 16S rDNA sequence using the Genbank BLAST tool revealed that isolated CQ2 was closely related to species of Pseudomonas genus and, thus, was entitled Pseudomonas sp. CQ2. The results of residual diesel oil contents measured by GC-MS showed that C7–C28 hydrocarbons could be degraded by Pseudomonas sp. CQ2. Thus, these findings revealed that CQ2 could be applied for remediation of diesel oil/petroleum-contaminated waters and soils on a large scale.