The Acute Impact of Arsenic As(III) on the Prokaryotic Community Composition and Selected Bacterial Strains Based on Microcosm Experiments

Abstract

In the present study, a 3-week microcosm experiment was conducted to assess the acute effect of arsenic trioxide [As(III)] at various concentrations (2.03, 4.06, 7.61, and 25.38 mM) on the bacterial communities. Water from a drinking water system (DWS) containing 6 µg/L (0.0000881 mM) of arsenic was used as a basis for microcosm experiments. Tolerance for As(III) of selectively isolated bacteria was checked based on optical density (OD) measurements which revealed As tolerance of Acidovorax facilis and Pseudomonas extremaustralis strains even at 25.38 mM of As(III). Compared to the control samples, the cell count values of the treated microcosms (DAS1_1, DAS2_1, DAS3_1 and DAS1_2, DAS2_2, DAS3_2) were higher by at least one or two orders of magnitude, even though, diversity indices, calculated from the NGS analysis, decreased. Results of NGS have shown that the structure of the bacterial community has changed as an effect of arsenic: representatives of Planctomycetes (3–6%) decreased while there was a proportional increase in the abundance of Proteobacteria (48–93%). Actinobacteria (2–8%), Bacteroidetes (4–7%), Patescibacteria (3–10%) and Verrucomicrobia (2–4%) were also abundant in the As(III)-treated microcosms. Phyla that contributes to less than 1% of the samples have disappeared already at 2.03 mM of As(III). The most frequent Archaea belonged to Nanoarchaeota (Woesearchaeia) (22–57%) and Thaumarchaeota (Nitrosopumilaceae) (9–40%) in both the control samples and microcosms with 2.03–23.38 mM of As(III). The cell structure of tested bacteria showed partial destruction after As(III) exposure. The ecotoxicological test revealed a cytotoxic effect above 6.67 mM concentration of As(III), genotoxicity could not be proven. Even though, microbes in our microcosms can be characterized by As(III) resistance and show measurable reactions to high As(III) concentrations, low concentrations of arsenic also trigger changes in the composition and diversity indices of the microbial communities. It is possible to cultivate arsenic tolerant microorganisms utilizing As(III) up to 25.38 mM to use them in bioremediation procedures contributing to water-purification processes.