Simultaneous petroleum hydrocarbon degradation and nitrogen removal by Acinetobacter sp. XF-5: Degradation mechanisms and temporal metabolic reprogramming.

Acinetobacter species capable of simultaneous total petroleum hydrocarbon degradation and heterotrophic nitrification-aerobic denitrification hold great promise for shale oil fracturing flowback fluid bioremediation. Nevertheless, metabolic regulation governing such coupled pollutant removal and enzyme-hydrocarbon multi-scale coupling mechanisms remain largely elusive. This study characterized the pollutant degradation performance and actual wastewater adaptability of Acinetobacter sp. XF-5, and explored core mechanisms underlying simultaneous total petroleum hydrocarbon degradation and efficient nitrogen removal via multi-omics analyses and molecular dynamics simulations. Under optimal conditions (sodium acetate as a co-metabolic substrate, a carbon/nitrogen ratio of 25, pH 7, 10% inoculum volume), strain XF-5 efficiently removed various nitrogen pollutants while degrading total petroleum hydrocarbon, with strong tolerance to high salinity and pollutant loads, and it can adapt to fracturing flowback fluid. This strain degraded aromatic compounds, and due to the substrate specificity of alkane monooxygenases encoded by strain XF-5, the degradation efficiency of various chain-length normal alkanes (C11-C31) exceeded 74.45%. Furthermore, multi-omics and nitrogen balance analyses indicated that its efficient nitrogen removal is likely driven by alternative enzymatic pathways, compensating for the absence of typical nitrification/denitrification genes. Crucially, the strain employs a 'temporal metabolic reprogramming' strategy to maintain carbon and electron homeostasis, shifting from ATP-intensive rapid proliferation to alkane-driven macromolecule synthesis under carbon limitation. This study addresses the transcriptomic and molecular mechanism gaps of dual-functional Acinetobacter sp., and provides a reliable strain resource and theoretical basis for the bioremediation of fracturing flowback fluid.