Mangroves are considered biodiversity hotspots threatened by various anthropogenic tensors such as pollution, which affect the taxonomic and functional diversity of microorganisms and therefore the stability of the ecosystem. Despite metagenomic work, knowledge of gene expression in contaminated mangroves is limited. Our general objective was to characterize the metatranscriptome at the taxonomic and functional level of bacteria associated with nutrient cycling and xenobiotic degradation of a mangrove contaminated by wastewater from the Colombian Caribbean. Total RNA was extracted from three soil samples from a mangrove affected by sewage for the construction of the cDNA library, and sequencing by the Illumina HiSeq 4000 platform. We found a domain of the phylum Firmicutes and Proteobacteria, represented mainly by Bacillus and Desulfuromonas respectively. Functional annotation showed high gene expression in metabolic pathways related to carbohydrate metabolism and processing of genetic information. Regarding biogeochemical cycles, the highest transcriptional activity was found in the assimilation of formaldehyde (methane metabolism), dissimilatory nitrate reduction (nitrogen metabolism), and reduction of sulfate (sulfur metabolism), which indicates a predominance of anaerobic processes and, decomposition of organic matter. Benzoate degradation was the pathway with the highest transcriptional activity in the degradation of xenobiotics. The predominance of few taxonomics could indicate selection of taxonomic groups by wastewater, advanced ecosystem degradation and loss of ecosystem resilience future.
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