Metagenome-based analysis of xenobiotic degradation potential in urban mangrove sediments under chronic anthropogenic impact.

Urban mangrove sediments receive continuous inputs of industrial and domestic pollutants, yet the microbial basis of pollutant transformation in these chronically impacted systems remains insufficiently resolved. This study investigated xenobiotic degradation potential in sediments from two urban mangrove locations along the Mandovi estuary, Goa, India, through reanalysis of previously generated shotgun metagenomic data. The assembled metagenomes showed enrichment of degradation pathways associated with aromatic and aliphatic pollutants commonly linked to urban contamination. A high representation of oxidoreductases and related aromatic transformation functions indicated that xenobiotic processing is closely linked to redox regulation and central carbon metabolism. Pathway completeness did not consistently correspond with relative abundance, suggesting that lower-abundance pathways may still retain structurally coherent degradation capacity. Hydrocarbon-specific annotation revealed the coexistence of aerobic and anaerobic activation strategies, consistent with adaptation to the redox heterogeneity of mangrove sediments. Xenobiotic- and hydrocarbon-associated functions were linked mainly to Pseudomonadota, Actinomycetota, Shewanella, and a substantial fraction of unresolved bacterial lineages, indicating that undercharacterized taxa may contribute importantly to pollutant-processing potential. Supportive metagenome-assembled genome analysis showed that recovered genomes encoded complementary subsets of degradation functions, although these genomes should be treated as illustrative examples rather than representatives of the whole community. Comparison between locations revealed similar core degradation functions but variation in secondary pathways, likely reflecting differences in local pollutant inputs and sediment conditions. These results show that urban mangrove microbiomes retain a functionally structured and redox-adapted metagenomic repertoire for xenobiotic and hydrocarbon degradation, highlighting their relevance to pollutant transformation, environmental monitoring, and native community-based bioremediation.