Ting Su

Elucidating microbial community shifts under polycyclic aromatic hydrocarbon (PAH) stress and screening indigenous PAH‐tolerant microbial resources are valuable for exploring potential bioremediation strategies for PAH‐contaminated mangrove ecosystems. In this study, surface sediments were collected from mangrove wetlands of the Maowei Sea, Guangxi, China. Three rounds of successive 7‐day enrichment cultures were performed with gradually elevated PAH concentrations using phenanthrene, anthracene, and pyrene as target carbon substrates, followed by isolation and taxonomic identification of PAH‐adapted bacteria. The results demonstrated that microbial community diversity decreased with increasing enrichment rounds and varied significantly among different PAH substrate treatments. ANOSIM confirmed significant differences in community structure across enrichment cycles and PAH treatments ( p < 0.01), consistent with the ordination patterns revealed by Non‐metric Multidimensional Scaling (NMDS). The PAH‐adapted microbial communities were predominantly dominated by Pseudomonadota (33.2%–99.9%), Bacillota (0%–48.3%), and Actinomycetota (0.1%–33.7%). In total, 17 indigenous PAH‐tolerant bacterial strains belonging to eight genera within the phylum Pseudomonadota were isolated, with representative strains affiliated with Labrys , Sphingomonas , and Acinetobacter . Within the tested physiological gradient ranges, Labrys sp. F3‐1 and Acinetobacter sp. B1‐5 exhibited optimal growth at pH 5.0, 40°C, and 15‰ salinity, while Sphingomonas sp. N2‐15 showed the best growth performance at pH 5.0, 25°C, and 4‰ salinity. Growth assays under PAH pressure further verified that these three isolates could survive and proliferate in PAH‐amended selective media under the tested laboratory conditions. This study provides indigenous PAH‐tolerant bacterial resources and fundamental community‐level insights for future investigations on microbial‐based remediation of PAH‐polluted mangrove sediments. Notably, the high PAH concentrations applied during laboratory enrichment (100–500 mg/L) were substantially higher than in situ environmental levels; the observed microbial responses and strain physiological traits reflect adaptive characteristics under extreme laboratory selective pressure and should be cautiously extrapolated to natural mangrove ecosystems.