Turning trash into treasure: Hermetia illucens microbiome and biodegradation of industrial side streams

Black soldier fly larvae (BSFL) have attracted attention due to their ability to upcycle various biological side streams into valuable biomass, such as proteins, lipids, and chitin. In this study, we investigated the impact of high-fiber diets on larval growth performance and the shift of microbes in the gut. We tested empty fruit bunches (EFB), potato pulp (PP), and cottonseed press cake (CPC), with chicken feed (CF) used as a control diet. We found that larvae reared on the EFB, PP, and CPC were smaller than control larvae at the end of development due to the low nutritional value of the diets. However, survival rates of more than 90% were observed regardless of the diet. We used a cultivation-dependent approach to analyze the microbial community in the gut of BSFL, isolated, and identified a total of 329 bacterial strains. Bacillaceae were most frequently isolated from larvae reared on the high-fiber EFB diet. These isolates were predicted to degrade cellulose in silico and this was subsequently confirmed in vitro using the Congo Red assay. Whereas the members of Enterobacteriaceae and Morganellaceae were mostly found in guts of larvae reared on the high-protein diets CPC and CF. We conclude that the gut microbiome plays a crucial role in the digestion of fiber-rich plant organic material, thereby enabling the BSFL to successfully complete their life cycle also on substrates with low nutritional value. As a result, BSFL convert industrial side streams into valuable biomass, reducing waste and promoting sustainability.