An cost-effective production of bacterial exopolysaccharide emulsifier for oil pollution bioremediation

The thermotolerant bacterium Geobacillus stearothermophilus DG1 was cultured with agroindustrial by-product molasses supplemented with NaNO3 and (NH4)2HPO3 to produce exopolysaccharides (EPSs) for the bioremediation of oil contamination. The EPSs produced under the optimal conditions contained a relatively high content of carbohydrates (60.32%), proteins (11.82%) and uronic acids (1.32%) as the main constituents. The EPSs successfully emulsified a range of hydrocarbons and exhibited excellent stability by thermal treatmanet and over a broad range of pH as well as a strong tolerance to different salinity levels. Additionally, hazardous constituents of the crude oil such as heteroaromatics, alkanes and alkyl cyclohexanes were readily degraded. A gene cluster containing 26 open reading frames (ORFs) responsible for EPS biosynthesis was isolated and characterised. Metabolic pathways related to EPS production and hydrocarbon degradation were reconstructed, and the analysis of the relationship between bioemulsion and biodegradation revealed that the EPSs enhanced petroleum hydrocarbon solubility and bioavailability, thereby promoting its uptake and utilization by microorganisms. This may also provide a carbon resource for sustainable bioremediation to generate sugar precursors for the synthesis of EPSs. Our results promoted the emulsification efficiency of crude oil and the findings illuminate the potential for EPS application in the bioremediation of hydrocarbons in different environments.