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Biomineralization of arsenate to arsenic sulfides is greatly enhanced at mildly acidic conditions.

ABSTRACT: Arsenic (As) is an important water contaminant due to its high toxicity and widespread occurrence. Arsenic-sulfide minerals (ASM) are formed during microbial reduction of arsenate (As(V)) and sulfate (SO4(2-)). The objective of this research is to study the effect of the pH on the removal of As due to the formation of ASM in an iron-poor system. A series of batch experiments was used to study the reduction of SO4(2-) and As(V) by an anaerobic biofilm mixed culture in a range of pH conditions (6.1-7.2), using ethanol as the electron donor. Total soluble concentrations and speciation of S and As were monitored. Solid phase speciation of arsenic was characterized by x-ray adsorption spectroscopy (XAS). A marked decrease of the total aqueous concentrations of As and S was observed in the inoculated treatments amended with ethanol, but not in the non-inoculated controls, indicating that the As-removal was biologically mediated. The pH dramatically affected the extent and rate of As removal, as well as the stoichiometric composition of the precipitate. The amount of As removed was 2-fold higher and the rate of the As removal was up to 17-fold greater at pH 6.1 than at pH 7.2. Stoichiometric analysis and XAS results confirmed the precipitate was composed of a mixture of orpiment and realgar, and the proportion of orpiment in the sample increased with increasing pH. The results taken as a whole suggest that ASM formation is greatly enhanced at mildly acidic pH conditions.

SUBMITTER: Rodriguez-Freire L

PROVIDER: S-EPMC4252821 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature

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Biomineralization of arsenate to arsenic sulfides is greatly enhanced at mildly acidic conditions.

Rodriguez-Freire Lucia L Sierra-Alvarez Reyes R Root Robert R Chorover Jon J Field James A JA

Water research 20140824

Arsenic (As) is an important water contaminant due to its high toxicity and widespread occurrence. Arsenic-sulfide minerals (ASM) are formed during microbial reduction of arsenate (As(V)) and sulfate (SO4(2-)). The objective of this research is to study the effect of the pH on the removal of As due to the formation of ASM in an iron-poor system. A series of batch experiments was used to study the reduction of SO4(2-) and As(V) by an anaerobic biofilm mixed culture in a range of pH conditions (6. ...[more]

PMID: 25222328

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Project description:Arsenate is a notorious toxicant that is known to disrupt multiple biochemical pathways. Many microorganisms have developed mechanisms to detoxify arsenate using the ArsC-type arsenate reductase, and some even use arsenate as a terminal electron acceptor for respiration involving arsenate respiratory reductase (Arr). ArsC-type reductases have been studied extensively, but the phylogenetically unrelated Arr system is less investigated and has not been characterized from Archaea Here, we heterologously expressed the genes encoding Arr from the crenarchaeon Pyrobaculum aerophilum in the euryarchaeon Pyrococcus furiosus, both of which grow optimally near 100°C. Recombinant P. furiosus was grown on molybdenum (Mo)- or tungsten (W)-containing medium, and two types of recombinant Arr enzymes were purified, one containing Mo (Arr-Mo) and one containing W (Arr-W). Purified Arr-Mo had a 140-fold higher specific activity in arsenate [As(V)] reduction than Arr-W, and Arr-Mo also reduced arsenite [As(III)]. The P. furiosus strain expressing Arr-Mo (the Arr strain) was able to use arsenate as a terminal electron acceptor during growth on peptides. In addition, the Arr strain had increased tolerance compared to that of the parent strain to arsenate and also, surprisingly, to arsenite. Compared to the parent, the Arr strain accumulated intracellularly almost an order of magnitude more arsenic when cells were grown in the presence of arsenite. X-ray absorption spectroscopy (XAS) results suggest that the Arr strain of P. furiosus improves its tolerance to arsenite by increasing production of less-toxic arsenate and nontoxic methylated arsenicals compared to that by the parent.IMPORTANCE Arsenate respiratory reductases (Arr) are much less characterized than the detoxifying arsenate reductase system. The heterologous expression and characterization of an Arr from Pyrobaculum aerophilum in Pyrococcus furiosus provides new insights into the function of this enzyme. From in vivo studies, production of Arr not only enabled P. furiosus to use arsenate [As(V)] as a terminal electron acceptor, it also provided the organism with a higher resistance to arsenate and also, surprisingly, to arsenite [As(III)]. In contrast to the tungsten-containing oxidoreductase enzymes natively produced by P. furiosus, recombinant P. aerophilum Arr was much more active with molybdenum than with tungsten. It is also, to our knowledge, the only characterized Arr to be active with both molybdenum and tungsten in the active site.

Dataset Information

Biomineralization of arsenate to arsenic sulfides is greatly enhanced at mildly acidic conditions.

Publications

Biomineralization of arsenate to arsenic sulfides is greatly enhanced at mildly acidic conditions.

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