Effect of the natural arsenic gradient on the diversity and arsenic resistance of bacterial communities of the sediments of Camarones River (Atacama Desert, Chile)

Abstract

Arsenic (As), a highly toxic metalloid, naturally present in Camarones River (Atacama Desert, Chile) is a great health concern for the local population and authorities. In this study, the taxonomic and functional characterization of bacterial communities associated to metal-rich sediments from three sites of the river (sites M1, M2 and M3), showing different arsenic concentrations, were evaluated using a combination of approaches. Diversity of bacterial communities was evaluated by Illumina sequencing. Strains resistant to arsenic concentrations varying from 0.5 to 100 mM arsenite or arsenate were isolated and the presence of genes coding for enzymes involved in arsenic oxidation (aio) or reduction (arsC) investigated. Bacterial communities showed a moderate diversity which increased as arsenic concentrations decreased along the river. Sequences of the dominant taxonomic groups (abundances ≥1%) present in all three sites were affiliated to Proteobacteria (range 40.3–47.2%), Firmicutes (8.4–24.8%), Acidobacteria (10.4–17.1%), Actinobacteria (5.4–8.1%), Chloroflexi (3.9–7.5%), Planctomycetes (1.2–5.3%), Gemmatimonadetes (1.2–1.5%), and Nitrospirae (1.1–1.2%). Bacterial communities from sites M2 and M3 showed no significant differences in diversity between each other (p = 0.9753) but they were significantly more diverse than M1 (p<0.001 and p<0.001, respectively). Sequences affiliated with Proteobacteria, Firmicutes, Acidobacteria, Chloroflexi and Actinobacteria at M1 accounted for more than 89% of the total classified bacterial sequences present but these phyla were present in lesser proportions in M2 and M3 sites. Strains isolated from the sediment of sample M1, having the greatest arsenic concentration (498 mg kg-1), showed the largest percentages of arsenic oxidation and reduction. Genes aio were more frequently detected in isolates from M1 (54%), whereas arsC genes were present in almost all isolates from all three sediments, suggesting that bacterial communities play an important role in the arsenic biogeochemical cycle and detoxification of arsenical compounds. Overall, results provide further knowledge on the microbial diversity of arsenic contaminated fresh-water sediments.

Seasonal variations in arsenic mobility and bacterial diversity: The case study of Huangshui Creek, Shimen Realgar Mine, Hunan Province, China

“…Significant differences in arsenic concentrations were observed in each site As1 (dry 120 µg g -1 ; wet 103 µg g -1 ), As4 (dry 590 µg g -1 ; wet 521 µg g -1 ), As7 (dry 964 µg g -1 ; wet 1310 µg g -1 ), As9 (dry 992 µg g -1 ; wet 1700 µg g -1 ); As12 (dry 564 µg g -1 ; wet 675 µg g -1 ). Concentrations of arsenic in samples As7 and As9 were the highest, and are comparable to those in other mining-affected river sediments (Azcue et al 1994, Leon et al 2018. Wet season arsenic concentrations in samples As7, As9 and As12 were higher than their respective dry season concentrations.…”

Reconstructing Draft Genomes Using Genome Resolved Metagenomics Reveal Arsenic Metabolizing Genes and Secondary Metabolites in Fresh Water Lake in Eastern India

“… 15 Therefore the possible occurrence of resistance genes related to arsenic (As) contamination in lake microbes can be investigated with genome resolved metagenomics approach. 75 - 78 Importantly, arsenic (As) resistant and metabolism-related genes were found to be present in the recovered genome bins of the lake sample ( Figure 5 and Supplementary Table S6 ); This is an indication that the mechanism to stabilize the Arsenic toxicity is already active in the lake microbes. The predominant forms of As in environment are inorganic arsenate (As [V]) and arsenite (As [III]).…”

Root microbiome assembly of As‐hyperaccumulator Pteris vittata and its efficacy in arsenic requisition

“…We demonstrated that the assembled bacterial and fungal genera inhabiting the root and rhizosphere compartments of P. vittata were reportedly involved in As cycling. For example, the bacterial genera Gemmatimonas, Lysobacter and Nitrospira are tolerant to high levels of As and are widely identified in As-contaminated environments, such as soil (Sun et al, 2019), rivers (Halter et al, 2011;Leon et al, 2018) and tailing dumps (Xiao et al, 2016a). Opitutus and Penicillium were identified as arsenate-reducing bacteria and are widely reported in Ascontaminated soils (Xiao et al, 2016c), activated sludge and coastal sediments (Cai et al, 2013).…”