Effect of chlorpyrifos on the earthworm Eudrilus euginae and their gut microbiome by toxicological and metagenomic analysis

The earthworms are important soil invertebrates and play a crucial role in pedogenesis. The application of pesticides and prolonged exposure to pesticides causes mortality of earthworms apart from profoundly affecting the resident gut microbiome. The microbiome plays a significant effect on the metabolic processes associated with earthworms. The pesticide Chlorpyrifos (CPF) was studied for its toxicity on Eudrilus euginae by toxicity studies. The LC50 value of filter paper contact test and acute toxicity test was 3.8 mg/mL and 180 mg/kg. The prolonged exposure of earthworms to pesticide on reproductive toxicity resulted in the mortality of earthworms and absence of cocoon formation. Further, the effects of CPF on the whole gut microbiome of E. euginae was analyzed using a long amplicon Nanopore sequencing. Results indicated no fluctuations with Firmicutes and Bacteroidetes, that were found to be dominant at bacterial phyla level while at the genus level, remarkable differences were noticed. Clostridium dominated the earthworm gut prior to CPF exposure while Bacillus dominated after exposure. Similarly, the fungal members such as Ascomycota and Basidiomycota were observed to dominate the gut of earthworm at the phyla level before and after exposure to CPF. In contrast, Clavispora (65%) was the dominant genus before CPF exposure and Taloromyces (42%) dominated after the CPF exposure. Our study demonstrates the effect of CPF on the mortality of E. euginae while the amplicon sequencing established the unique microbiome of the gut in response to the CPF exposure. [GRAPHICS] .