Bacterial community succession during the enrichment of chemolithoautotrophic arsenite oxidizing bacteria at high arsenic concentrations

Arsenic Contamination of Groundwater Is Determined by Complex Interactions between Various Chemical and Biological Processes

At a great many locations worldwide, the safety of drinking water is not assured due to pollution with arsenic. Arsenic toxicity is a matter of both systems chemistry and systems biology: it is determined by complex and intertwined networks of chemical reactions in the inanimate environment, in microbes in that environment, and in the human body. We here review what is known about these networks and their interconnections. We then discuss how consideration of the systems aspects of arsenic levels in groundwater may open up new avenues towards the realization of safer drinking water. Along such avenues, both geochemical and microbiological conditions can optimize groundwater microbial ecology vis-à-vis reduced arsenic toxicity.

Biofilm formation of Ancylobacter sp. TS-1 on different granular materials and its ability for chemolithoautotrophic As(III)-oxidation at high concentrations

The oxidation of arsenic (As) is a key step in its removal from water, and biological oxidation may provide a cost-effective and sustainable method. The biofilm-formation ability of Ancylobacter sp. TS-1, a novel chemolithoautotrophic As oxidizer, was studied for four materials: polypropylene, graphite, sand, and zeolite. After seven days under batch mixotrophic conditions, with high concentrations of As(III) (225 mg·L^-1), biofilm formation was detected on all materials except for polypropylene. The results demonstrate As(III)-oxidation of TS-1 biofilms and suggest that the number of active cells was similar for graphite, sand, and zeolite. However, the biofilm biomass follows the specific surface area of each material: 7.0, 2.4, and 0.4 mg VSS·cm^-3 for zeolite, sand, and graphite, respectively. Therefore, the observed biofilm-biomass differences were probably associated with different amounts of EPS and inert biomass. Lastly, As(III)-oxidation kinetics were assessed for the biofilms formed on graphite and zeolite under chemolithoautotrophic conditions. The normalized oxidation rate for biofilms formed on these materials was 3.6 and 1.0 mg·L^-1·h^-1·cm^-3, resulting among the highest reported values for As(III)-oxidizing biofilms operated at high-As(III) concentrations. Our findings suggest that biofilm reactors based on Ancylobacter sp. TS-1 are highly promising for their utilization in As(III)-oxidation pre-treatment of high-As(III) polluted waters.

Artificial light at night alter the impact of arsenic on microbial decomposers and leaf litter decomposition in streams

Artificial light at night (ALAN, also known as light pollution) has been proved to be a contributor to environmental change and a biodiversity threat worldwide, yet little is known about its potential interaction with different metal pollutants, such as arsenic (As), one of the largest threats to aquatic ecosystems. To narrow this gap, an indoor microcosm study was performed using an ALAN simulation device to examine whether ALAN exposure altered the impact of arsenic on plant litter decomposition and its associated fungi. Results revealed that microbial decomposers involved in the conversion of As(III) to As(V), and ALAN exposure enhanced this effect; ALAN or arsenic only exposure altered fungal community composition and the correlations between fungi species, as well as stimulated or inhibited litter decomposition, respectively. The negative effects of arsenic on the decomposition of Pterocarya stenoptera leaf litter was alleviated by ALAN resulting in the enhanced photodegradation of leaf litter lignin and microbiological oxidation of As(III) to As(V), the increased microbial biomass and CBH activity, as well as the enhanced correlations between CBH and litter decomposition rate. Overall, results expand our understanding of ALAN on environment and highlight the contribution of ALAN to the toxicity of arsenic in aquatic ecosystems.

Ample Arsenite Bio-Oxidation Activity in Bangladesh Drinking Water Wells: A Bonanza for Bioremediation?

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.

Isolation and identification of the native population bacteria for bioremediation of high levels of arsenic from water resources

Health of millions of people is threatened by the risk of drinking arsenic-contaminated water worldwide. Arsenic naturally conflicts with the concept of life, but recent studies showed that some microorganisms use toxic minerals as the source of energy. Hence, the researchers should consider the development of cost-effective and highly productive procedures to remove arsenic. The current study was conducted on a native bacterial population of Seyed-Jalaleddin Spring Kurdistan, Iran. Accordingly, the arsenic amount in water samples was measured >500 μg/L by the two field and in vitro methods. Water samples were transferred to laboratory and cultured on chemically defined medium (CDM) with arsenic salts. A total of 14 native arsenic-resistant bacterial strains were isolated and after providing pure culture and performing biochemical tests, the isolates were identified using polymerase chain reaction (PCR) and 16s rRNA genomic sequencing. The potential of bacterial strains for the biotransformation of arsenic was assessed by the qualitative assessment of AgNO₃ method and efficiency of arsenic speciation was determined for the first time by silver diethyldithiocarbamate (SDDC) method with an error of less than 5%. Among the isolated strains, only strain As-11 and strain As-12 showed arsenic transformation characteristics and were registered in NCBI database by the access numbers KY119262 and KY119261, respectively. Results of the current study indicated that strain As-11 had the potential of biotransformation of As(V) to As(III) and vice versa with the efficiency of 78% and 48%, respectively. On the other hand, strain As-12 had the potential for biotransformation of As(V) to As(III) and vice versa with the efficiency of 28% and 45%, respectively.