Leveraging indigenous Bacillus consortia for heavy oil biodegradation and soil bioremediation

Fast biodegradation of heavy oil contaminants remains a major challenge in the bioremediation of oil-contaminated soil. The use of bacterial consortia containing Bacillus species is a promising strategy for cleaning up contaminated soil. The aim of this study was to develop heavy oil-degrading indigenous bacterial consortia and evaluate their biodegradation performance and bioremediation potential. Four heavy oil-degrading Bacillus strains (designated S1 to S4) were isolated and screened out from oilfield wastewater and oil sludge samples collected in the Karamay Oilfield in Xinjiang, China. S1 was tentatively identified as B. halotolerans, S2 and S6 as B. subtilis, and S4 as B. paralicheniformis. Five consortia were developed through free combination of the four strains. Two consortia (S1 +S2 +S4 and S1 +S2 +S6) showed high efficiencies of heavy oil degradation and heavy metal extraction. Up to 34.5 % of heavy oil was degraded using bacterial consortia after 30 days, which was notably higher than the maximum efficiency of single strains (20 %). The greatest extraction efficiencies of bacterial consortia for iron (87.9 %), vanadium (46.0 %), and nickel (60.0 %) were greater than those of single strains (72.7 %, 31.6 %, and 56.2 %, respectively). In a simulated bioremediation experiment, up to 35.3 % of total petroleum hydrocarbons were from oil sludge using bacterial consortia, with particularly high efficiencies for long-chain n-alkanes (C₂₀–C₂₆: 59.1 %; C₂₈–C₃₂: 61.1 %). This study demonstrates the outstanding performance of indigenous Bacillus consortia in degrading heavy oil and petroleum hydrocarbons in oil sludge, with great application potential for soil bioremediation.