Soil Bacterial Community and Earthworms: Hand-in-Hand First Responders to Pesticides

Earthworms and microbial communities represent a large fraction of soil living biomass and play an essential role in soil functioning. They are also important non-target organisms in soil and sub-lethal dose toxicity assessment represents a decisive step for the regulatory authorities to evaluate the collateral impact of pesticides. Here we present a study where we evaluated through High Throughput Sequencing (HTS) of 16S rDNA amplicons the sub-lethal impact of spinosyn and organophosphate based pesticides on soil bacteria with or without earthworms during 28d long experiment. We found that community composition were changing over time rapidly starting from the first day with the most significant impact on the 7th and 14th days. Formation of hierarchical clusters mainly as a function of time and then treatments in the presence/absence of earthworms was observed. Multivariate canonical correspondence analysis that assessed the pesticides, earthworm's presence and their combined impact at the beginning (1d) and at the end of the experiments (28d) marked further differences caused by various treatments at the beginning of the experiments and fade-out phenomenon as time passed by. Specific OTUs with previously reported pesticide degradation potential and earthworm gut microbiota presence were also singled out as the main drivers of change in soil microbial community. Overall, these findings clearly indicated the buffering effect earthworms had on the bacterial communities starting from earliest sampling (1d) until the final sampling (28d) as well as bacterial community members’ degradation response to pesticides over time.