Microbiome characterization of urbanized lakes impacted by legacy arsenic contamination

Bacteria and other microbes are important contributors to arsenic
biotransformation processes, which can alter the bioavailability and
toxicity of arsenic within a contaminated environment. Multispecies
biofilms, known as periphyton, have been identified as a significant site
of arsenic bioaccumulation within shallow freshwater lakes impacted by
legacy arsenic contamination. We hypothesized that prolonged arsenic
exposure results in the formation of distinct prokaryotic communities
within the periphyton and other environmental compartments in
arsenic-contaminated lakes compared to uncontaminated lakes. We also
predicted that the periphyton prokaryotic communities would be distinct
from, but partially overlapping with, those found in the surrounding water
column and nearby littoral sediment. To test these hypotheses, we
determined the taxonomic composition and modeled the assembly processes
that yielded the bacterial communities found within three environmental
compartments (periphyton, littoral sediment, and water column) of three
lakes that had been differentially impacted by legacy arsenic
contamination. We identified unique microbiomes within these environmental
compartments and observed a clear shift in microbial community composition
within high arsenic-contaminated periphyton. Hyperaccumulation of arsenic
(~400 ppm) in the periphyton correlated with non-random (deterministic)
selection for prokaryotic taxa that are more related than expected by
chance (homogenizing selection). We also identified key prokaryotic genera
within the arsenic-contaminated periphyton that suggest prolonged arsenic
contamination may shift iron and methane biogeochemical cycles, which may
regulate arsenic accumulation and mobilization. Our results imply that
legacy arsenic contamination, by altering bacterial community composition
and metabolic potential at the base of the food web, may influence
biogeochemical and nutrient cycles at a larger scale within a freshwater
lake ecosystem.