Abstract
Millions of people worldwide are at risk of arsenic poisoning from their drinking water. In Bangladesh the problem extends to rural drinking water wells, where non-biological solutions are not feasible. In serial enrichment cultures of water from various Bangladesh drinking water wells, we found transfer-persistent arsenite oxidation activity under four conditions (aerobic/anaerobic; heterotrophic/autotrophic). This suggests that biological decontamination may help ameliorate the problem. The enriched microbial communities were phylogenetically at least as diverse as the unenriched communities: they contained a bonanza of 16S rRNA gene sequences. These related to Hydrogenophaga, Acinetobacter, Dechloromonas, Comamonas, and Rhizobium/Agrobacterium species. In addition, the enriched microbiomes contained genes highly similar to the arsenite oxidase (aioA) gene of chemolithoautotrophic (e.g., Paracoccus sp. SY) and heterotrophic arsenite-oxidizing strains. The enriched cultures also contained aioA phylotypes not detected in the previous survey of uncultivated samples from the same wells. Anaerobic enrichments disclosed a wider diversity of arsenite oxidizing aioA phylotypes than did aerobic enrichments. The cultivatable chemolithoautotrophic and heterotrophic arsenite oxidizers are of great interest for future in or ex-situ arsenic bioremediation technologies for the detoxification of drinking water by oxidizing arsenite to arsenate that should then precipitates with iron oxides. The microbial activities required for such a technology seem present, amplifiable, diverse and hence robust.
Highlights
Arsenic toxicity of water constitutes a, sometimes ill-recognized but substantial problem in many countries and on all continents [1,2,3]
The anaerobic arsenite oxidizing cultures with nitrate as potential electron acceptor, initiated from wells Mn-40.1, Mn-40.2 and Mn-40.3, all engaged in arsenite oxidation, irrespective of whether or not acetate had been included as source of organic carbon (AHAO; anaerobic heterotrophic arsenite oxidation) and electrons (AAO; anaerobic chemolithoautotrophic arsenite oxidation) (Table 1C: Anaerobic-Chemolithoautotrophic (AAO) and Heterotrophic (AHAO) and As(III) Oxidation (AAO), respectively)
Arsenite oxidase genes could be amplified in all these chemolithoautotrophic or heterotrophic, aerobic or anaerobic, arsenite-oxidizing enrichments, whenever arsenite oxidation had been observed (Table 1, see further below)
Summary
Arsenic toxicity of water constitutes a, sometimes ill-recognized but substantial problem in many countries and on all continents [1,2,3]. Subsurface arsenic removal (SAR) has been proposed based on subsurface iron removal (SIR) as alternative method to remove the arsenic from the drinking water [6] The principle of this technology is the in-situ removal of iron along with arsenic. Under the same aerobic conditions, arsenite is oxidized abiotically to arsenate [1] This process was proposed to remove arsenic from the mobile water phase, if not already reducing arsenic toxicity: arsenite [As(III)] is >25 times more toxic than arsenate [As(V)] [2,3]. Implementations of this SAR have not yet reduced arsenic to levels below drinking-water safety standards . The abiotic oxidation of arsenite is too slow [7,8]
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