Diversity and Functions of Epilithic Riverine Biofilms

This article relates epilithic dry- and wet-seasonal bacterial biofilm composition to water quality along Río de la Sabana near Acapulco, Mexico. Samples were taken from various locations including nearly pristine upland locations, adjacent to residential floodplain developments, and immediately upstream from an estuarine lagoon. Bacterial composition was identified through sequential DNA analysis at the phylum, class, order, and family levels, with most of these categorized as heterotrophs, autotrophs, denitrifiers, nitrogen fixers, pathogens, and/or potential bioremediators based on generalized literature-sourced assignments. The results were interpreted in terms of location by extent of effluent pollution, and by dry versus wet seasonal changes pertaining to biofilm composition, related bacterial functions, and the following water quality parameters: temperature, pH, dissolved oxygen, biological and chemical oxygen demand, fecal and total bacteria counts, methylene blue active substances, electrical conductivity, and nitrite, nitrate, ammonium, sulfate, and phosphate concentrations. It was found that epilithic bacterial biofilm diversity was richest during the wet season, was more varied in abundance along the upland locations, and was dominated by Proteobacteria and Bacteroidetes with bioremediation and pathogen functions along effluent-receiving river locations. Low-abundance families associated with anaerobic and denitrifying functions were more prevalent during the wet season, while low-abundance families associated with aerobic, N 2 -fixing and pH-elevating functions were more prevalent during the dry season.