Production of biosurfactant by a Pseudomonas aeruginosa isolate and its applicability to in situ microbial enhanced oil recovery under anoxic conditions

Abstract

Compared to ex situ application, in situ application of biosurfactants for microbial enhanced oil recovery (MEOR) is relatively cost-effective, and lack of oxygen in oil reservoirs is a bottleneck for in situ production of biosurfactants by mostly isolated biosurfactant-producing bacteria. Furthermore, few microorganisms can produce biosurfactants under anoxic conditions. A bacterial strain identified as Pseudomonas aeruginosa SG (GenBank accession number KJ995745) was isolated from Xinjiang oil field, and it can produce biosurfactant under anoxic conditions. Different organic substrates (glucose, sucrose, glycerol, corn steep powder, starch, molasses, soybean oil, sunflower oil) were tested to determine the optimal carbon source for anoxic production of biosurfactant by SG. Strain SG anaerobically grew well at temperatures (25–40 °C), pH (6.0–9.0), and salinity (0–30 g L⁻¹ of NaCl), respectively. Thin layer chromatography and Fourier transform infrared spectroscopy revealed that the SG biosurfactant produced under anoxic conditions was similar to rhamnolipid. SG biosurfactant could reduce air–water surface tension from 71.6 to 33.3 mN m⁻¹, and reduce oil–water interfacial tension from 26.1 to 2.14 mN m⁻¹. And a critical micelle concentration value of 80 mg L⁻¹ was obtained. Moreover, the biosurfactant displayed good emulsifying activity over hydrocarbons and crude oil. A core flooding test revealed that an extra 8.33% of original crude oil in the core was displaced through the in situ production of rhamnolipid by SG. The potential use of the isolated SG for in situ MEOR application was discussed. And bioaugmentation of SG in Xinjiang oil reservoirs will be a promising approach for in situ MEOR.