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Alkaline sulfide-rich hot springs provide a unique environment for microbial community and arsenic (As) biogeochemistry. In this study, a representative alkaline sulfide-rich hot spring, Zimeiquan in the Tengchong geothermal area, was chosen to study arsenic geochemistry and microbial community using Illumina MiSeq sequencing. Over 0.26 million 16S rRNA sequence reads were obtained from 5-paired parallel water and sediment samples along the hot spring's outflow channel. High ratios of As(V)/AsSum (total combined arsenate and arsenite concentrations) (0.59-0.78), coupled with high sulfide (up to 5.87 mg/L), were present in the hot spring's pools, which suggested As(III) oxidation occurred. Along the outflow channel, AsSum increased from 5.45 to 13.86 μmol/L, and the combined sulfide and sulfate concentrations increased from 292.02 to 364.28 μmol/L. These increases were primarily attributed to thioarsenic transformation. Temperature, sulfide, As and dissolved oxygen significantly shaped the microbial communities between not only the pools and downstream samples, but also water and sediment samples. Results implied that the upstream Thermocrinis was responsible for the transformation of thioarsenic to As(III) and the downstream Thermus contributed to derived As(III) oxidation. This study improves our understanding of microbially-mediated As transformation in alkaline sulfide-rich hot springs.

Arsenic biogeochemistry has been studied extensively in acid sulfate-chloride hot springs, but not in acid sulfate hot springs with low chloride. In this study, Zhenzhuquan in Tengchong geothermal area, a representative acid sulfate hot spring with low chloride, was chosen to study arsenic geochemistry and microbial community structure using Illumina MiSeq sequencing. Over 0.3 million 16S rRNA sequence reads were obtained from 6-paired parallel water and sediment samples along its outflow channel. Arsenic oxidation occurred in the Zhenxhuquan pool, with distinctly high ratios of arsenate to total dissolved arsenic (0.73-0.86). Coupled with iron and sulfur oxidation along the outflow channel, arsenic accumulated in downstream sediments with concentrations up to 16.44 g/kg and appeared to significantly constrain their microbial community diversity. These oxidations might be correlated with the appearance of some putative functional microbial populations, such as Aquificae and Pseudomonas (arsenic oxidation), Sulfolobus (sulfur and iron oxidation), Metallosphaera and Acidicaldus (iron oxidation). Temperature, total organic carbon and dissolved oxygen significantly shaped the microbial community structure of upstream and downstream samples. In the upstream outflow channel region, most microbial populations were microaerophilic/anaerobic thermophiles and hyperthermophiles, such as Sulfolobus, Nocardia, Fervidicoccus, Delftia, and Ralstonia. In the downstream region, aerobic heterotrophic mesophiles and thermophiles were identified, including Ktedonobacteria, Acidicaldus, Chthonomonas and Sphingobacteria. A total of 72.41-95.91% unassigned-genus sequences were derived from the downstream high arsenic sediments 16S rRNA clone libraries. This study could enable us to achieve an integrated understanding on arsenic biogeochemistry in acid hot springs.

A survey was carried out on the microbial community of 20 groundwater samples (4 low and 16 high arsenic groundwater) and 19 sediments from three boreholes (two high arsenic and one low arsenic boreholes) in a high arsenic groundwater system located in Hetao Basin, Inner Mongolia, using the 454 pyrosequencing approach. A total of 233,704 sequence reads were obtained and classified into 12-267 operational taxonomic units (OTUs). Groundwater and sediment samples were divided into low and high arsenic groups based on measured geochemical parameters and microbial communities, by hierarchical clustering and principal coordinates analysis. Richness and diversity of the microbial communities in high arsenic sediments are higher than those in high arsenic groundwater. Microbial community structure was significantly different either between low and high arsenic samples or between groundwater and sediments. Acinetobacter, Pseudomonas, Psychrobacter and Alishewanella were the top four genera in high arsenic groundwater, while Thiobacillus, Pseudomonas, Hydrogenophaga, Enterobacteriaceae, Sulfuricurvum and Arthrobacter dominated high arsenic sediments. Archaeal sequences in high arsenic groundwater were mostly related to methanogens. Biota-environment matching and co-inertia analyses showed that arsenic, total organic carbon, SO4(2-), SO4(2-)/total sulfur ratio, and Fe(2+) were important environmental factors shaping the observed microbial communities. The results of this study expand our current understanding of microbial ecology in high arsenic groundwater aquifers and emphasize the potential importance of microbes in arsenic transformation in the Hetao Basin, Inner Mongolia.

A survey of bacterial and archaeal community structure was carried out in 10 shallow tube wells in a high arsenic groundwater system located in Hetao Basin, Inner Mongolia by 16S rRNA gene based two-step nested PCR-DGGE, clone libraries and 454 pyrosequencing. 12 bacterial and 18 archaeal DGGE bands and 26-136 species-level OTUs were detected for all the samples. 299 bacterial and 283 archaeal 16S rRNA gene clones for two typical samples were identified by phylogenetic analysis. Most of the results from these different methods were consistent with the dominant bacterial populations. But the proportions of the microbial populations were mostly different and the bacterial communities in most of these samples from pyrosequencing were both more abundant and more diverse than those from the traditional methods. Even after quality filtering, pyrosequencing revealed some populations including Alishewanella, Sulfuricurvum, Arthrobacter, Sporosarcina and Algoriphagus which were not detected with traditional techniques. The most dominant bacterial populations in these samples identified as some arsenic, iron, nitrogen and sulfur reducing and oxidizing related populations including Acinetobacter, Pseudomonas, Flavobacterium, Brevundimonas, Massilia, Planococcus, and Aquabacterium and archaeal communities Nitrosophaera and Methanosaeta. Acinetobacter and Pseudomonas were distinctly abundant in most of these samples. Methanogens were found as the dominant archeal population with three methods. From the results of traditional methods, the dominant archaeal populations apparently changed from phylum Thaumarchaeota to Euryarchaeota with the arsenic concentrations increasing. But this structure dynamic change was not revealed with pyrosequencing. Our results imply that an integrated approach combining the traditional methods and next generation sequencing approaches to characterize the microbial communities in high arsenic groundwater is recommended.

Vertical distribution of bacterial communities was detected in high arsenic (As) sediments in a representative high As area in Inner Mongolia. Nineteen sediment samples were collected from a 30 m borehole and detected by geochemistry and molecular ecological approaches including polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), 16S rRNA gene clone library and 454 pyrosequencing. As contents ranged from 42.1 to 111.3 mg kg(-1) which fluctuated with different depth and significantly high in clay and mild clay sediment samples at depth of 8, 20, 25 and 28 m respectively. The ratios of As(III) to total As generally increased with depth but As(V) dominated in all sediment samples. High concentrations of total As, sulfur, iron and total organic carbon were generally found in clay and low in sand samples. Both DGGE patterns and 454 pyrosequencing results indicated that bacterial communities dynamically diversified with increasing depth and were dominated by Firmicutes, Bacteroidetes, Proteobacteria and Chloroflexi. Most of the sediment samples were dominated by populations including Sporosarcina, Acinetobacter, Pseudomonas, Halomonas, Polaromonas, Paenibacillus and Flavobacterium. These populations were found with high similarities with those microbes capable of denitrification, sulfur oxidation, organic matter degradation and As resistance and reduction. These results implied that microbes might play an important role in As mobilization in the shallow aquifers of Hetao Plain, Inner Mongolia.

Kelp is a traditional healthy food due to its high nutritional content; however, its relatively high contents of iodine and arsenic have raised concerns about its edible safety. This study explored the effects of different cooking treatments on the contents of iodine and arsenic in kelp, evaluated the bioaccessibility and bioavailability of iodine and arsenic in kelp using in vitro digestion, and compared the differences in the transport characteristics of iodine in kelp and KIO3 using a Caco-2 monolayer cell transport model. The results show that the content of target elements that reached systemic circulation could be reduced by cooking and gastrointestinal digestion. The highest reductions in iodine and arsenic were 94.4% and 74.7%, respectively, which were achieved by boiling for 10 min. The bioaccessibility and bioavailability of iodine and arsenic were significantly improved by a cooking treatment. However, the contents of iodine and arsenic decreased significantly, with the bioaccessibility of iodine reducing from 3188.2 μg/L to 317.0 μg/L and that of arsenic reducing from 32.5 μg/L to 18.1 μg/L in the gastric phase after boiling. The findings also show that the efficiency of iodine transport in kelp and KIO3 was positively correlated with the transport time and negatively correlated with the concentration of iodine. With the increase in the iodine concentration, the rate of iodine transport in kelp decreased from 63.93% to 3.14%, but that of KIO3 was stable at around 35%, which indicates that the absorption efficiency of iodine from kelp was limited, even when too much kelp was ingested. In conclusion, the edible safety of kelp is significantly improved after cooking. The risk of excessive iodine and arsenic intake caused by consuming kelp is extremely low, and as an effective iodine supplement source, kelp has higher edible safety compared with KIO3. This study clarifies the safety of algae based on iodine and arsenic contents and also provides a basis for the formulation of food safety standards. [ABSTRACT FROM AUTHOR]

The abundance, diversity, and relative distribution of sulfate-reducing bacteria (SRB) in high arsenic (As) groundwater aquifers of Hangjinhouqi County in the Hetao Basin, Inner Mongolia was investigated using denaturing gradient gel electrophoresis (DGGE) and quantitative polymerase chain reaction (qPCR) analysis ofdsrBgenes (encoding dissimilatory sulfite reductase beta-subunit). DGGE results revealed that SRB populations were diverse, but were mainly composed ofDesulfotomaculum,Desulfobulbus,Desulfosarcina, andDesulfobacca. The abundance ofDesulfobulbuswas positively correlated with the ratio of Fe(II)/Fe(III). Although qPCR results showed that thedsrBgene abundance in groundwater samples ranged from below detection to 4.9 × 106copies/L, and the highest percentage ofdsrBgene copies to bacterial 16S rRNA gene copies was 2.1%. Geochemical analyses showed that As(III) content and the ratio of Fe(II) to Fe(III) increased with total As, while sulfate concentrations decreased. Interestingly, thedsrBgene abundance was positively correlated with As concentrations. These results indicate that sulfate reduction occurs simultaneously with As and Fe reduction, and might result in increased As release and mobilization when As is not incorporated into iron sulfides. This study improves our understanding of SRB and As cycling in high As groundwater systems. [ABSTRACT FROM AUTHOR]

To detect arsenic geochemistry and evaluate its environmental risk, 30 geothermal water samples were collected from Rehai and Ruidian geothermal fields of Tengchong, China. There were three main water types including SO 4 and Na-Cl-HCO 3 types in Rehai and Na-HCO 3 type in Ruidian. Arsenic concentrations ranged from 22.1 to 1150.3 μg L −1 . Relative high concentrations of arsenic with an average of 495.1 μg L −1 , as well as K, Na, F, Cl, Li and B, were detected in neutral or alkaline geothermal water samples, which suggested that rock leaching in geothermal reservoir was the main resource of arsenic enrichment in geothermal water. Comparatively, those acid geothermal water samples which were formed by vapor rich in H 2 S condensing and oxidizing in the shallow groundwater or surface water had lower arsenic concentrations with an average of 77.1 μg L −1 . The ratios of arsenite to total arsenic widely ranged from 0.01 to 0.97 and were determined by mixing proportions of geothermal water and shallow groundwater or surface water. Furthermore, there was a significantly positive correlation between arsenic with HCO 3 (R = 0.81, P = 0.01). These results implied that shallow groundwater or surface water in Tengchong geothermal area had been probably contaminated by arsenic due to the mixing of geothermal water. [ABSTRACT FROM AUTHOR]