Spatial patterns in the abundance and expression of heavy metal resistance genes in Yucatán coastal microbiomes

Heavy metal pollution poses a growing threat to coastal ecosystems; however, its impact on the bacterial communities that inhabit them remains underexplored. Here, we present the first metatranscriptomic analysis of heavy metal resistance genes (HMRGs) in coastal bacterial communities along the Yucatán Peninsula. At four sites, ranging from well-preserved mangroves to coastal areas impacted by human activity, we detected 2,916 HMRG transcripts linked to resistance against 23 metals. Our results reveal spatial patterns in taxonomic and genetic abundance, as well as in transcriptional activity, reflecting differences in gene-level diversity across sites. The phylum Proteobacteria dominated the taxonomic profiles, while at the family level, less studied groups such as Myxococcaceae and Merismopediaceae emerged as potential reservoirs of novel resistance mechanisms. The abundance of HMRG transcripts increased along a west–east gradient, with the lowest levels at El Palmar and the highest at Progreso. Resistance genes for copper, zinc, arsenic, and nickel were prevalent at all analyzed sites, reflecting ecological risk. The presence of multi-metal resistance genes suggests possible co-selection with antibiotic resistance genes. Expression patterns revealed site-specific variation: conserved sites showed broader gene diversity and broad-spectrum expression, while impacted sites showed lower expression. Notably, Progreso showed the highest abundance of HMRG transcripts but the lowest overall expression.