Environmental drivers of bacterial diversity, distribution, and predicted metabolic potential in Hainan Island mangrove sediments

Mangrove sediments harbor highly diverse microbial communities essential to biogeochemical cycling and ecosystem functioning. However, island-scale patterns linking environmental gradients, bacterial diversity, community distribution, and secondary metabolic potential remain unclear. We used high-throughput 16S rRNA amplicon sequencing and sediment physicochemical analyses to investigate bacterial communities across 12 representative mangrove habitats on Hainan Island, China. Bacterial diversity varied substantially among sites (Shannon indices: 5.24–6.98); and community composition was consistently dominated by Proteobacteria, Firmicutes, and Actinobacteria. Electrical conductivity, available nitrogen, and total potassium were identified as the primary environmental variables associated with community structure. Significant correlations between microbial β-diversity and environmental dissimilarity indicated that environmental variation was associated with bacterial community differentiation at the island scale. Biosynthetic gene clusters (BGCs) were predicted based on taxonomic profiles. The predicted biosynthetic landscape revealed spatial differentiation across sampling sites and was classified into nonribosomal peptide, post-translationally modified peptide, and terpene-enriched metabolic types. Environmental factors, including available phosphorus, water content, and pH, were associated with variation in specific predicted BGC classes. This island-scale survey shows that environmental gradients across Hainan Island are associated with bacterial diversity, community distribution, and predicted secondary metabolic potential in mangrove sediments. These findings provide insights into the ecological organization of mangrove sediment microbiomes and highlight mangrove sediments as reservoirs of microbial and predicted biosynthetic diversity.