Biotransformation of selenium and arsenic in multi-species biofilm

Environmental context Elevated levels of selenium and arsenic in the environment as a result of anthropogenic activities are creating significant concerns for the health of aquatic ecosystems. How biofilms, or aquatic microbial communities, interact with and chemically modify selenium and arsenic species has been examined. The results demonstrate that selenium and arsenic induce structural changes in biofilms, and concurrently undergo extensive biotransformation, in most cases to less bioavailable species. Abstract Arsenic and selenium are both elements of concern especially when released into the environment by anthropogenic activity. Biofilms, or communities of microorganisms, can play important roles in biotransforming elements to less toxic chemical forms. This study used novel tools to characterise the fate of oxyanions (selenate, selenite, arsenate or arsenite) in multi-species biofilms inoculated from a source receiving coal mining effluent. Confocal laser scanning microscopy (CLSM) demonstrated a distinct biofilm morphology at elevated oxyanion concentrations. Selenium and arsenic K near-edge X-ray absorption spectroscopy (XAS) showed biofilm biotransformation of oxyanions; extended X-ray absorption fine structure (EXAFS) confirmed elemental selenium as a product. Micro X-ray fluorescence imaging combined with CLSM revealed highly localised reduced selenium species in the biofilm. Isolation and partial 16S rRNA gene sequencing suggested four principle bacterial genera were responsible. Biofilms can both detoxify and sequester selenium and arsenic, playing critical roles in their fate and effects in aquatic environments.