Comparative Hydrocarbon Biodegradation by Bacillus haikouensis and Cytobacillus kochii: Pure Culture versus Consortium Performance

This study aimed to investigate indigenous hydrocarbon-tolerant bacteria from a coastal environment and evaluate the bioremediation potential. Water samples were collected from high-risk oil spill areas and mixed with motor oil to find hydrocarbon-tolerant bacteria with potential uses in bioremediation. Two prospective bacterial isolates were selected for inhibition zone test, biochemical analysis, enzymatic assay, and 16S rDNA gene sequencing. The isolates were identified as Cytobacillus kochii (PQ500563) and Bacillus haikouensis (PQ395181). Phylogenetic trees constructed using the Neighbor-Joining (NJ) method confirmed the taxonomic placement with high similarity to known strains. The results showed that C. kochii degraded hydrocarbons, with an inhibition zone of 10 ± 0.55 mm, while B. haikouensis had an inhibition zone of 8 ± 1.05 mm. C. kochii had the highest dehydrogenase activity of 20.67 ± 0.22 × 10-2 μmol/min/ml, suggesting that the bacteria was very good at breaking down hydrocarbons and forming biomass. The isolate B. haikouensis had the highest catechol 2,3-dioxygenase activity of 75.90 ± 0.14 × 10-2 μmol/min/ ml, which signified being very good at breaking down aromatic chemicals. The combination of C. kochii and B. haikouensis as the consortium had a synergistic enhancement, providing significantly higher activities for key catabolic enzymes (dehydrogenase, catechol 2,3-dioxygenase, and catalase) along with increased biomass production compared to the individual pure cultures. This showed the superior efficacy of the consortium, which was driven by complementary enzymatic strengths for degrading diverse hydrocarbons in marine oil spill contexts.