Impact of exposure to arsenic on the bacterial microbiota associated with river biofilms in the Pampas region

Freshwater contamination by arsenic (As) is a worldwide problem. It may be found in Pampean streams of Argentina at concentrations higher than those recommended by international organizations and stipulated by national regulations. Exposure to high As concentrations causes serious consequences to both human health and the environment. The general objective of this work was to evaluate the effect of As on the biofilm microbiota structure from Naveira stream, Luján, Province of Buenos Aires (Coordinates: 34º34′02 "S 59º03′51" W). The biofilm collected was cultivated in glass aquaria at different As III concentrations (0, 0.2 and 20 mg / L), inside incubation chambers under controlled conditions (16h light: 8h dark and 24 ± 1°C) and constant aeration for 31 d, with partial water renewal every 9 d. We amplified the hypervariable regions V3 and V4 of the bacterial 16S rRNA gene from biofilm bacterial community samples to determine the diversity and abundance of the different taxa. The taxonomic composition of each sample, the alpha diversity of each treatment and the main metabolic pathways were analyzed. Principal Component Analysis of the present phyla and a Linear Discriminant Analysis of the metabolic pathways was also performed. Significant changes were observed in relation to the taxonomic composition of the bacterial community after exposure to the metalloid. However, this effect was not observed at the low concentration used (0.2 mg / L), which is the one that corresponds to ecologically relevant levels. The significantly affected phyla were Verrucomicrobiota, Acidobacteriota, Patescibacteria, Hydrogenedentes and WPS-2. The relative abundances of the Verrucomicrobiota, WPS-2 and Patescibacteria groups were notably decreased in the treatment with high As, while the Acidobacteria group was increased in both treatments with As. The stream samples showed greater bacterial diversity than those grown in the laboratory without As. Finally, it was possible to characterize the metabolic profile of the biofilm developed under natural conditions in the leaves of the aquatic plant Elodea canadensis in the Naveira stream. In addition, results showed that biosynthesis-related pathways were more abundant at the high As concentration treatment (20 mg / L).