Functional profiles and organochlorine degradation potential in microbial communities of tropical epilithic biofilms: a case study in Guadeloupe (Lesser Antilles)

This study investigates the composition, structure, and predictive associated functions of epilithic bacteria living in the biofilms of a freshwater (FWR) and a mixed-saline (MSR) tropical river. High-throughput sequencing revealed a 69% overlap in species richness between the two sites. Cyanobacteria were dominant in freshwater, while heterotrophic classes like Alphaproteobacteria and Betaproteobacteria were prevalent in the mixed-saline biofilm. Predictive functional analysis (FAPROTAX) indicated greater diversity in MSR, favoring organic matter degradation and nutrient cycling, with more bacterial OTUs involved in chemoheterotrophy and hydrogen oxidation (Wilcoxon, <i>p</i> > 0.001). In contrast, FWR had a higher abundance of OTUs linked to phototrophy and degradation of aromatic compounds and plastics (Wilcoxon, <i>p</i> > 0.001). Key microbial interactions were revealed between phototrophic cyanobacteria and heterotrophs such as <i>Fulvivirga</i> (Cytophagia), suggesting a pivotal role for this genus in the carbon cycle. Additionally, bacterial species known for their ability to remove chlorine from pollutants, such as <i>Acidovorax, Acinetobacter, Comamonas, Curvibacter</i>, <i>Sediminibacterium</i>, or bacterial species belonging to the Sphingomonadaceae family were more diverse and abundant in FWR site. These findings point to promising bioremediation potential driven by biofilm community activities, particularly in tropical freshwater environments impacted by organochlorine contaminants.