Characterisation and effectiveness evaluation of microbial biosurfactants for their use in oil spill response

Abstract

Surfactants are a group of amphiphilic chemical compounds (i.e. having both hydrophobic and hydrophilic domains) that form an indispensable component in almost every sector of modern industry. Their significance is evidenced from the enormous diversity of applications they are used in, ranging from food and beverage, agriculture, public health, healthcare/medicine, textiles, oil & gas, and bioremediation. This PhD aimed to investigate two hydrocarbon-degrading bacterial strains, Halomonas sp. stain TGOS-10 and Pseudomonas sp. strain MCTG214(3b1), for their ability to produce biosurfactants and their usefulness for oil spill response. For this, three strategies were developed. First, the two strains were screened for production of surface-active compounds using sustainable substrates such as glucose and sunflower oil. Surface-active compounds were extracted, purified and their chemical structure was characterised with carbohydrate and amino acid assays, and NMR. Results revealed that both stains produced surface-active compound, TGOS-10 strain produced both an emulsifier and surfactant when grown on different substrates, whereas MCTG214(3b1) strain produced only surfactant. Second, the extracted and purified surfactants were tested for dispersion effectiveness at different concentrations and three oil types by utilising a standard baffled flask test. Both biosurfactants dispersed the crude oil at varying efficiencies depending on concentration and oil type but generally TGOS-10 showed better dispersing results than MCTG214(3b1). Lastly, in a case study from the northeast Atlantic, Illumina MiSeq sequencing was used to determine the response of the natural microbial community when exposed to either chemically-dispersed crude oil (commercial dispersant Finasol) or biosurfactant-dispersed oil (rhamnolipid from P. aeruginosa). In addition, parallel microcosms to determine hydrocarbon degradation were performed and analysed with Gas-Chromatography coupled with Flame Ionization Detection (GC-FID). During incubation for 4 weeks in roller-bottle microcosms, members of psychrophilic oil-degrading Colwellia and Oleispira initially dominated the microbial community in both the rhamnolipid and Finasol treatments. Thereafter, the community structure of these treatments significantly delineated. The microbial diversity was significantly greater in the treatment amended with rhamnolipid compared to that in the dispersant-amended treatment. GC-FID/MS analysis revealed that oil biodegradation was markedly enhanced in the Finasol-amended treatment. However, the “better-performing” qualities of the chemical dispersant Finasol may be in part, at least, conferred by other components that constituent its formulation, and biosurfactants, such as rhamnolipid, could potentially be developed into dispersant formulations with much improved qualities. Ecological null models were also used to better understand and quantify the relative importance of ecological processes in the assembly of microbial communities.