Enrichment hydrocarbon‑degrading bacterial communities from the southern Gulf of Mexico in long‑term stored sediments.

The Gulf of Mexico is chronically exposed to petroleum hydrocarbons from natural seeps and anthropogenic activities, sustaining diverse microbial communities capable of hydrocarbon degradation. To investigate natural bacterial succession associated with long-term hydrocarbon degradation, sediment samples from shallow (< 1000 m) and deep (> 2500 m) sites in the southern Gulf of Mexico were incubated at 4 °C for up to 24 months. Temporal changes in bacterial community composition were analyzed by 16S ribosomal RNA gene sequencing, and residual hydrocarbons were quantified by gas chromatography-mass spectrometry. Initial communities differed significantly between shallow and deep sediments but remained stable during the first six months before shifting markedly after 12 months of incubation. Gammaproteobacteria, Alphaproteobacteria, and Bacteroidota increased in relative abundance, whereas Deltaproteobacteria declined. Genera such as Colwellia, Alcanivorax, Shewanella, and Neptunomonas, which include well-known hydrocarbon-degrading species, displayed dynamic, time-dependent enrichment patterns. Chemical analyses revealed substantial depletion of alkanes and polycyclic aromatic hydrocarbons, indicating sustained biodegradation activity. These results demonstrate that Gulf of Mexico sediment communities harbor metabolically resilient consortia capable of long-term hydrocarbon mineralization under low-temperature, dark conditions. The integrated microbial and geochemical data provide new insights into ecological succession and the persistence of hydrocarbon-degrading bacteria in deep-sea sediments, contributing to a better understanding of natural attenuation processes in petroleum-impacted marine environments.