Isolation of nitrate-reducing bacteria from an offshore reservoir and the associated biosurfactant production.

Biosurfactant producing nitrate-reducing bacteria (NRB) in anaerobic reservoir environments are closely associated with souring (H ₂ S) control in the offshore oil and gas industry. Five NRB strains were screened from offshore produced water samples and all were identified as Pseudomonas stutzeri . Their biosurfactant producing abilities when fed on either glucose or glycerol media were investigated. P. stutzeri CX3 reduced the medium surface tension to 33.5 and 29.6 mN m ^-1 , respectively, while growing on glucose or glycerol media. The CX3 strain was further inoculated to examine its growth performance, resulting in 32.4% and 94.5% of nitrate consumption over 228 hours of monitoring in two media, respectively. The composition analysis of the biosurfactant product generated by P. stutzeri CX3 was conducted through thin-layer chromatography, gas chromatography with a flame ionization detector (FID) and Fourier transform infrared spectroscopy (FT-IR). The biosurfactant product was identified as a mixture of a small part of lipopeptides and a large part of glycolipids while its critical micellar concentration (CMC) was as low as 35 mg L ^-1 . The biosurfactant product demonstrated high stability over a wide range of temperature (4-121 °C), pH (2-10), and salinity (0-20% w/v) concentration. The results provided valuable technical and methodological support for effective offshore reservoir souring control and associated enhanced oil recovery activities.
Competing Interests: The authors declare no conflict of interest.
(This journal is © The Royal Society of Chemistry.)