Genomic Analysis Reveals Distinct Strategies for Hydrocarbon Degradation and Salt Adaptation in Two Screened Halotolerant Bacteria

Abstract Petroleum hydrocarbon contamination in saline-alkali environments poses a significant challenge for efficient bioremediation due to the inhibitory effects of high salinity on microbial activity. In this study, two halotolerant hydrocarbon-degrading strains were isolated from petroleum-contaminated saline-alkali soil and identified as Acinetobacter calcoaceticus DA01 and Bacillus enclensis DA02. Strains DA01 and DA02 exhibited efficient degradation of n-hexadecane under high salinity (1.5 M NaCl), with degradation efficiencies of 69.94% and 71.64%, respectively. Whole-genome analysis revealed significant differences between the two strains in terms of hydrocarbon degradation pathways, substrate utilization potential, and salt stress response mechanisms. DA01 harbors AlkB-mediated pathways for linear alkane degradation, has the capacity to degrade aromatic compounds, and relies on biofilm formation and ion-regulatory systems for salt tolerance. DA02 features P450-associated oxidation systems with capability for complex substrates, and efficient osmoadaptation via transporters and compatible solute uptake. This study provides new insights into the distinct molecular strategies enabling stable hydrocarbon degradation under high salinity conditions and offers valuable microbial resources and functional genes for the bioremediation of petroleum-contaminated saline environments.