Isolation and characterization of efficient diesel-degrading, biosurfactant biosurfactant-producing bacteria from petroleum-contaminated subsurface soils in Kandy District, Sri Lanka

Abstract

Petroleum contamination is a prevalent environmental issue, with detrimental effects extending across diverse ecosystems. Among the numerous hydrocarbons present in petroleum, diesel is a major contributor to soil pollution. Previous studies have identified bacteria as highly effective agents for diesel degradation (DD), highlighting their potential for bioremediation of oil spills. However, successful bioremediation of diesel-contaminated environments requires the identification of effective diesel-degrading microbial strains, along with key traits that support DD, such as biosurfactant production. Therefore, this study aimed to identify efficient diesel-degrading bacteria (DDB) from petroleum-contaminated sites in Kandy District, while concurrently exploring their biosurfactant production capabilities. DDB were isolated using Bushnell-Haas broth supplemented with diesel. Pure bacterial isolates were obtained by streak and spread plating techniques. Isolated bacteria were identified through morphological and biochemical methods. The DD efficiencies of the isolates were examined by turbidity assay and 2,6-dicholophenolindophenol (DCPIP) assays. Moreover, efficient DDB were used to design artificial consortia. The degradation efficiencies of artificial consortia and natural consortia were also evaluated. Additionally, the biosurfactant production ability of efficient DDB was investigated by the emulsification test, oil displacement test, and CTAB agar plates. Among the diesel-degrading bacterial strains isolated, the four most effective isolates, in the order of decreasing efficiency, belonged to the genera Pseudomonas (83.04%), Staphylococcus (71.84%), Corynebacterium (62.61%), and Streptococcus (60.50%). Further, the DD efficiencies of most of the designed consortia and natural consortia were found to be significantly higher than those of the individual bacterial isolates, with one natural consortium containing Pseudomonas, Staphylococcus, and Corynebacterium that outperformed the designed consortia. Moreover, the isolated Pseudomonas and Staphylococcus strains were identified as biosurfactant producers, suggesting that their ability to produce biosurfactants contributes to their highest DD efficiencies. The findings of this study can be used in developing locally adaptable bioremediation strategies for diesel-contaminated sites in Sri Lanka.