Copper and chlorpyrifos stress affect the gut microbiota of chironomid larvae (Propsilocerus akamusi)

Chironomids are characterized by their ubiquitous distribution, global diversity and tolerant ability to deal with environmental stressors. To our knowledge, this is the first study presenting the gut microbial structure of chironomid larvae and examining the microbial alteration induced by invading chlorpyrifos and copper with different dosages. Lethal bioassay displayed a significantly decreased percentage survival of Propsilocerus akamusi larvae exposed to 800 mg/L copper and 50 mu g/L chlorpyrifos at 96 h. Larvae with deficient gut microbiota exhibited a depressed level of glutathione S-transferase activity after stressful exposure. The high-throughput 16S rRNA gene sequencing was adopted to investigate the community structure and it turned out that both copper and chlorpyrifos were able to generate distinguished variations of gut microbiota in the stressor-specific and concentration-dependent manner. Of note, the relative abundance of Comamonas, Stenotrophomonas, and Yersinia remarkably elevated in the presence of copper while chlorpyrifos exposure upregulated the prevalence of certain genera (e.g. Serratia). Flavobacterium was greatly attenuated in chlorpyrifos group with lethal dosage exhibiting more severe impacts. The predicted gene functions of the gut commensals differed between normal samples and those subjected to distinct toxins. Besides, more positive associations and limited modularity of microbial interactions were observed in stressor-challenged larvae, presenting a network with impaired complexity and stability. The appearance of either copper or chlorpyrifos exhibited strong positive correlations with genera belonging to Proteobacteria and Firmicutes. Collectively, this investigation introduces a general outline of gut microbiota obtained from chironomid individuals with latent adaptive tactics to nocuous factors (heavy metal and pesticide), which could build a fundamental basis for us to further explore the protective roles of chironomid gut bacterial colonizers in defending against aquatic contaminants.