Silent bacteria: Intrinsic bioremediation potential in the sediments of Lake Faro (Messina, Italy)

Lake sediments can act as reservoirs for contaminants and host microbial communities with potential roles in natural ecosystem functioning. This study explored the occurrence of hydrocarbon-degrading bacteria, including "silent" hydrocarbon-responsive populations detectable after selective enrichment, in interfacial sediments of Lake Faro, a brackish meromictic basin in Messina, Italy. Sediment samples collected from five stations were chemically characterized and incubated in microcosms enriched with tetradecane, phenanthrene, or crude oil as the sole carbon and energy source. Chemical analyses revealed that hydrocarbons HCs > 12 were below the quantification limit at all stations, while PAHs were detectable at low concentrations. After 80 days of enrichment, microbial abundance increased, especially in tetradecane and crude oil-amended microcosms, and hydrocarbon-degrading bacteria were selectively enriched. Overall, 25 bacterial isolates were obtained, of which 16 were identified by 16S rRNA gene sequencing and assigned to taxa with reported hydrocarbon-degrading potential, including Isoalcanivorax pacificus, Marinobacter hydrocarbonoclasticus, Pseudoalteromonas sp., Vibirio alginolyticus, and Stappia indica. Several strains showed emulsifying activity, with E₂₄ values up to 60%. These findings suggest that Lake Faro sediments host a latent hydrocarbon-responsive bacterial fraction, with intrinsic bioremediation potential and ecological relevance for natural attenuation processes in transitional aquatic ecosystems.