Soil Hg Contamination Impact on Earthworms’ Gut Microbiome

Abstract

Mercury (Hg) is one of the most toxic heavy metals and is known for its persistence in the environment and potential to accumulate along the food chain. In many terrestrial polluted sites, earthworms are in direct contact with Hg contamination by ingesting large quantities of soil. However, little is known about the impact of Hg soil pollution on earthworms’ gut microbiome. In this study, two incubation experiments involving earthworms in soils from a long-term Hg-polluted site were conducted to assess: (1) the effect of soil Hg contamination on the diversity and structure of microbial communities in earthworm, cast and soil samples; and (2) how the gut microbiome of different digestive track parts of the earthworm responds to soil Hg contamination. The large accumulation of total Hg and methyl-Hg within the earthworm tissues clearly impacted the bacterial and fungal gut community structures, drastically decreasing the relative abundance of the dominating gut bacterial class Mollicutes. Hg-tolerant taxa were found to be taxonomically widespread but consistent along the different parts of the earthworm digestive tract. This study revealed that although Hg might not directly affect the health of macro-organisms in the food-web such as earthworms, their metabolism and legacy in the soil might be impacted through changes in their gut microbiome.

Attributes of Drying Define the Structure and Functioning of Microbial Communities in Temperate Riverbed Sediment

“…We ran a non-metric multidimensional scaling (NMDS) PERMANOVA ( adonis function, “vegan” package) to assess the β-diversity community structure and pairwise post-hoc tests to assess differences among sediment types, drying intensities and drying durations at the ASV-level. For each drying treatment, after 10, 30, or 90 days of drying, we calculated the log2-fold change response of ASV’s count from each bacterial and fungal at class-level relative to the corresponding before-drying ASV’s assembly, using the “Deseq” package ( Brantschen et al, 2020 ). Positive significant log2-fold change responses were defined as tolerant ASVs and negative change responses were defined as sensitive.…”

Special Issue on Bioconversion, Bioaccumulation and Toxicity of Mercury in a Changing World

“…As such, it is hypothesized to play a major role in the exposure of the host to dietary pollutants, including Hg. Two papers studied the impact of Hg on microbiota [4,6]. The paper authored by Brantschen et al revealed changes in microbiota of earthworms exposed to Hg contaminated soils [6].…”

“…Two papers studied the impact of Hg on microbiota [4,6]. The paper authored by Brantschen et al revealed changes in microbiota of earthworms exposed to Hg contaminated soils [6]. Data pointed out that the health of macro-organisms in the food web might be impacted through changes in their gut microbiome, subsequently affecting their metabolism and legacy in the soil [6].…”

“…In 2013, the nations of the world agreed on the first global treaty to mitigate the many deleterious health outcomes associated with Hg release into the environment and MMHg exposure. In this context, all the papers in this Special Issue provide innovative insights into the Hg fate in the aquatic and terrestrial ecosystems and increase the understanding of the Hg biogeochemical cycle [1][2][3][4][5][6].…”