Regulation of antimicrobial peptides in Hermetia illucens in response to fungal exposure

The black soldier fly (Hermetia illucens) is important in antimicrobial peptides (AMP) research due to its exposure to diverse microbial environments. However, the impact of different fungal exposures on AMP abundance in H. illucens has not been thoroughly explored. Our study focused on basal conditions and interactions with three fungi: the non-pathogenic Candida tropicalis (isolated from larval gut), Saccharomyces cerevisiae, and the pathogenic Beauveria bassiana. Using RNA-seq and LC-MS/MS, we found that under standard conditions, the majority of AMPs belonged to the Lysozyme, Cecropin, and Defensin classes, with Defensins exhibiting the highest quantification levels. Exposure to any of the fungi upregulated AMP gene expression, indicating immune activation. Notably, exposure to C. tropicalis and B. bassiana led to notable downregulation of AMPs in H. illucens larvae compared to S. cerevisiae, suggesting these fungi may suppress or modulate the host immune response to aid their survival and colonization. The immune response of H. illucens larvae revealed that S. cerevisiae and B. bassiana trigger similar AMP pathways, whereas C. tropicalis elicits a distinct response with upregulation of Defensins and Cecropins. Lysozymes, known for their antibacterial and antifungal activity, were upregulated in response to S. cerevisiae and B. bassiana, but downregulated with C. tropicalis, potentially facilitating fungal survival in the larvae's gut. This suggests that C. tropicalis adapts to reduce immune pressure, while B. bassiana may suppress AMPs to persist. Understanding these mechanisms opens possibilities for leveraging AMPs in combating C. tropicalis, which is implicated in human diseases. Overall design: To study how pathogenic and non-pathogenic fungi affect the mRNA expression levels of AMP genes in H. illucens, we raised H. illucens larvae on a standard diet supplemented with different fungi: B. bassiana, S. cerevisiae, C. tropicalis, and a control group (no fungi added). Four days after the fungal treatment we extracted RNA from the fat bodies and performed RNA-seq analysis.We conducted differential expression analysis for the different treatments relative to the control using all expressed genes and then focused specifically on AMP-expressed genes in subsequent analyses.