Biological arsenic oxidation has been suggested as a key biogeochemical process that controls the mobilization and fate of this metalloid in aqueous environments. To the best of our knowledge, only four aerobic chemolithoautotrophic arsenite-oxidizing (CAO) bacteria have been shown to grow via direct arsenic oxidation and to have the essential genes for chemolithoautotrophic arsenite oxidation. In this study, a new CAO bacterium was isolated from a high Andean watershed evidencing natural dissolved arsenic attenuation. The bacterial isolate, designated TS-1, is closely related to the Ancylobacter genus, in the Alphaproteobacteria class. Results showed that TS-1 has genes for arsenite oxidation and carbon fixation. The dependence of bacterial growth from arsenite oxidation was demonstrated. In addition, a mathematical model was suggested and the kinetic parameters were obtained by simultaneously fitting the biomass growth, arsenite depletion curves, and arsenate production. This research increases the knowledge of chemolithoautotrophic arsenic oxidizing microorganisms and its potential role as a driver for natural arsenic attenuation.

The study of electrochemically active microorganisms (EAMs) has revealed the metabolic versatility of chemolithoautotrophic microorganisms in bioelectrochemical systems (BESs). However, direct electron uptake from electrodes to support bacterial growth has been suggested only for the iron oxidiser Mariprofundus ferrooxydans, the sulfur oxidiser bacterium Thiobacillus denitrificans and the iron/sulfur oxidiser Acidithiobacillus ferrooxidans. To the best of our knowledge, chemolithoautotrophic arsenite oxidisers (CAOs) have not been reported as biocathodic EAM. This paper studies the electrochemical activity of Ancylobacter sp. TS‐1, a new CAO. The electrochemical capacity of TS‐1 was evidenced by linear sweep voltammetry tests, revealing a peak of cathodic current dependent on biomass concentration at −500 mV (vs. Ag/AgCl, at pH 7.2); and by chronoamperometry, showing an increase in the cathodic current over time. Cathodic currents obtained for TS‐1 (9.5±2.4 μA/cm2) are comparable with values previously reported for A. ferrooxidans (∼27 μA/cm2) and M. ferrooxydans (∼8 μA/cm2). Scanning electron micrographs show TS‐1 cells on electrodes during the chronoamperometry, suggesting biofilm development of strain TS‐1 when using the cathode only as an electron donor. Hence, TS‐1 not only enlarges the list of known biocathodic EAMs, but also paves the way for novel BES applications on arsenic electro‐bioaugmentation and bioremediation.

No abstract

Bioelectrochemical systems (BESs) have been extensively studied for treatment and remediation. However, BESs have the potential to be used for the enrichment of microorganisms that could replace their natural electron donor or acceptor for an electrode. In this study, Winogradsky BES columns with As-rich sediments extracted from an Andean watershed were used as a strategy to enrich lithotrophic electrochemically active microorganisms (EAMs) on electrodes (i.e., cathodes). After 15 months, Winogradsky BESs registered power densities up to 650 μWcm−2. Scanning electron microscopy and linear sweep voltammetry confirmed microbial growth and electrochemical activity on cathodes. Pyrosequencing evidenced differences in bacterial composition between sediments from the field and cathodic biofilms. Six EAMs from genera Herbaspirillum, Ancylobacter, Rhodococcus, Methylobacterium, Sphingomonas, and Pseudomonas were isolated from cathodes using a lithoautotrophic As oxidizers culture medium. These results suggest that the tested Winogradsky BES columns result in an enrichment of electrochemically active As-oxidizing microorganisms. A bioelectrochemical boost of centenarian enrichment approaches, such as the Winogradsky column, represents a promising strategy for prospecting new EAMs linked with the biogeochemical cycles of different metals and metalloids.