Arsenic is the most ubiquitous environmental toxin and enters our environment in many ways, including weathering of rocks, mining, volcanic activities, herbicides, wood preservatives, feed additives and so on. Arsenate (As(V)) is the predominant species in the aerobic soils and be ingested and accumulated by non-target soil organisms via ingestion and dermal contact. Soil fauna is an important component of soil ecosystem, and its gut bacteria plays a crucial role in enhancing the host metabolism, health and immunity. Some studies have focused on the survival and reproduction of soil animals exposed to arsenic contamination. However, comprehensive studies of the interactions between arsenic species and the gut bacterial flora of soil animals have not been undertaken and relationships between arsenic species and ABGs in the soil fauna gut are not well understood. In this study, five important soil organisms involved in organic matter decomposition and nutrient turnover including the macrofauna (two earthworms) and three mesofauna (isopoda, enchytraeid and collembolan) were treated with arsenic. High-throughput quantitative PCR (HT-qPCR) with 80 primer sets (79 arsenic biotransformation genes (ABGs), and the bacterial 16S rRNA gene) was used to investigate the distribution of ABGs in different soil fauna. The gut microbial community was evaluated by using 16S rRNA gene amplification and high-throughput sequencing. The results showed that arsenic can be accumulated by all five soil animal body tissues. The profiles of ABGs in the gut of different animal species were various, though genes involved in arsenic reduction and efflux were predominant in all soil fauna gut. Gut bacterial community of soil fauna were significantly influenced by arsenic and animal ecological species. In addition, perturbation of gut microbiota can exert an impact on the abundance of ABGs. Our study characterizes the first time the distribution of ABGs in the gut of different soil animals and help understand the role of gut microbiota in the arsenic biotransformation.

Keywords: soil animals; arsenic; gut microbial community; arsenic biotransformation genes