Convergent shifts in microbial communities: Petroleum hydrocarbon contamination suppresses matrix heterogeneity.

Accurate characterization of microbial communities in aquifers is essential for understanding groundwater ecosystem responses to petroleum hydrocarbon contamination. However, existing studies have focused primarily on groundwater, largely overlooking the coupled interactions between groundwater and aquifer sediments, which may bias aquifer-scale evaluations of microbial functional potential. In this study, contaminated groundwater and corresponding aquifer sediment samples were collected from a petroleum hydrocarbon impacted site, together with uncontaminated groundwater and sediment samples outside the contaminant plume as controls. Petroleum hydrocarbon concentrations and principal component analysis (PCA) revealed comparable contamination levels in groundwater and aquifer sediments. Integrating 16S rRNA gene sequencing analysis and metagenomic sequencing analysis, we found that microbial communities in contaminated groundwater exhibited broader niche breadth, higher niche overlap, and increased representation of low-molecular-weight carbon (LMW-C) metabolism, particularly pathways associated with ribose and amino sugar utilization. In contrast, aquifer sediment communities showed higher abundances of multidrug efflux pump genes and functional pathways involved in naphthalene and benzene degradation (PAH-C and MAH-C). Further correlation and community assembly analyses indicated that petroleum hydrocarbon contamination was the primary driver shaping microbial communities in both matrices, overriding intrinsic physicochemical differences. Meanwhile, sediment-specific properties, such as stronger sorption capacity for organic matter and differences in microbial lifestyles contributed to the observed divergence between groundwater and sediment communities. Overall, this study demonstrates that contamination induced selection dominates microbial community assembly in aquifers, and provides a mechanistic basis for improving the evaluation of natural attenuation potential and informing remediation strategies in contaminated aquifer systems.