Heavy hydrocarbons as selective substrates for isolation of asphaltene degraders: A substrate-based bacterial isolation strategy for petroleum hydrocarbon biodegradation

Increasing instances of petroleum hydrocarbon (PHC) spills and the release of crude oil sludge into the environment necessitate the implementation of effective remediation strategies. A microorganism or a consortium that can effectively degrade the various complex hydrocarbons (HCs) present in such spills and sludge is still unavailable. Moreover, most studies in the literature use pure model HCs. As PHCs contain both aromatic and aliphatic components, we hypothesized that these compounds could serve as substrates for the enrichment of bacteria with diverse metabolic properties. Subsequently, we used specific crude oil fractions for the isolation of bacterial strains that could potentially act on crude oil sludge. This led to the isolation of six bacterial strains (identified as Pseudomonas putida, Pseudomonas mendocina, Bacillus cereus, Bacillus marisflavi, Lysinibacillus fusiformis, and Ochrobactrum intermedium) that possessed the ability to degrade asphaltenes, the most recalcitrant constituent in oil sludge, to varying degrees (9%-30%). Of the isolated bacteria, the highest asphaltene removal of 30% was obtained with O. intermedium. All six isolates when cultured with HCs, produced biosurfactants (0.15-0.5 gL(-1)), which have been previously associated with the solubilization and assimilation of HCs by microorganisms. Moreover, a mixed culture composed of the above isolates was able to achieve 39%, 49%, and 55% degradation of the crude oil fractions 500 N, lube oil, and deasphalted oil, respectively, in 15 days. Further, the isolates were capable of degrading both aromatic and aliphatic HCs of different chain lengths. The levels of the C21-C30, C31-C35, and C36-C60 HCs decreased by 13%-54%, 49%-70%, and 39%-60%, respectively, upon biodegradation by the mixed culture, thus indicating the versatile nature of microbial metabolism. Through our study, we demonstrate that mixed substrates such as crude HCs act as effective realistic substrates for the isolation of microbes that facilitate diverse substrate degradation. (c) 2020 Elsevier B.V. All rights reserved.