Arsenic disturbs the gut microbiome of individuals in a disadvantaged community in Nepal

Abstract

Arsenic is ubiquitous in nature, highly toxic, and is particularly abundant in Southern Asia. While many studies have focused on areas like Bangladesh and West Bengal, India, disadvantaged regions within Nepal have also suffered from arsenic contamination levels, with wells and other water sources possessing arsenic contamination over the recommended WHO and EPA limit of 10 μg/L, some wells reporting levels as high as 500 μg/L. Despite the region's pronounced arsenic concentrations within community water sources, few investigations have been conducted to understand the impact of arsenic contamination on host gut microbiota health. This study aims to examine differential arsenic exposure on the gut microbiome structure within two disadvantaged communities in southern Nepal. Fecal samples (n = 42) were collected from members of the Mahuawa (n = 20) and Ghanashyampur (n = 22) communities in southern Nepal. The 16S rRNA gene was amplified from fecal samples using Illumina-tag PCR and subject to high-throughput sequencing to generate the bacterial community structure of each sample. Bioinformatics analysis and multivariate statistics were conducted to identify if specific fecal bacterial assemblages and predicted functions were correlated with urine arsenic concentration. Our results revealed unique assemblages of arsenic volatilizing and pathogenic bacteria positively correlated with increased arsenic concentration in individuals within the two respective communities. Additionally, we observed that commensal gut bacteria negatively correlated with increased arsenic concentration in the two respective communities. Our study has revealed that arsenic poses a broader human health risk than was previously known. It is influential in shaping the gut microbiome through its enrichment of arsenic volatilizing and pathogenic bacteria and subsequent depletion of gut commensals. This aspect of arsenic has the potential to debilitate healthy humans by contributing to disorders like heart and liver cancers and diabetes, and it has already been shown to contribute to serious diseases and disorders, including skin lesions, gangrene and several types of skin, renal, lung, and liver cancers in disadvantaged areas of the world like Nepal.

Keywords: Arsenic; Gut microbiome; Microbiology; Nepal; Public health; Well water.

Figure 1

Average species richness measures.

Figure 2

Observed species rarefaction curve of Community.

Figure 3

Cladogram comparing differences in significantly enriched taxa between the two communities.

Figure 4

Comparison of differences in community composition between samples. A) Mahuawa and B) Ghanashyampur community.

Figure 5

Correlation plots analyzing bacterial correlations with arsenic concentration in urine. The size of the dot and the color indicate strength of the correlation. Dark blue indicates a strong positive correlation while dark red indicates a strong negative correlation. (A) Correlations between arsenic concentration in urine and bacterial taxa within the Mahuawa community. (B) Correlations between arsenic concentration and bacterial taxa within the Ghanashyampur community. Plotted correlations all have a p-value less than 0.05.

Figure 6

Cladograms comparing significantly enriched taxa within the Mahuawa community (A) High vs. Undetected Categories (B) Moderate Vs. Undetected Categories.

Figure 7

Cladograms comparing significantly enriched taxa within the Ghanashyampur community Arsenic Exposure Levels (A) High vs. Undetected (B) Moderate vs. Undetected.