Bioconversion of cyanobacteria by black soldier fly larvae (Hermetia illucens L.): Enhancement by antioxidants

Microcystin-Lr-Induced Changes in Growth Performance, Intestinal Microbiota, and Lipid Metabolism of Black Soldier Fly Larvae (Hermetia illucens)

Biological treatment by black soldier fly larvae (BSFL) has proven to be an effective method for the resource utilization of cyanobacteria, but the effects of microcystin-LR (MC-LR) in cyanobacteria on BSFL growth have not been adequately explored. To evaluate the inhibitory effect and toxic mechanism of MC-LR on BSFL, the growth performance and intestinal microbiota were examined after exposure to 0, 10, 100, and 1000 μg/kg of MC-LR. The larval weight and survival rate were each significantly inhibited by 21.53% and 21.49% compared with the control group, respectively, after exposure at a concentration of 1000 μg/kg MC-LR for 16 days. Lipid accumulation, intestinal inflammation, and oxidative stress were observed in three treatment groups, with dose-dependent inflammation ocurring in the intestine. Compared with the control group, superoxide dismutase and catalase activity levels were significantly increased by 74.91% and 49.58%, respectively, which confirmed the occurrence of oxidative stress induced by MC-LR. Furthermore, MC-LR altered the diversity of intestinal microbiota and increased the relative abundance of pathogenic bacteria (e.g., Paenibacillus, Clostridium_sensu_stricto_1, and Lachnoclostridium), which increased the risk of disease in BSFL and contributed to observed metabolic disorders. On the other hand, qRT-PCR analysis further confirmed the occurrence of oxidative stress and the activation of the peroxisome proliferator-activated receptor signaling pathway, resulting in the upregulation of fatty acid synthesis-related genes, ultimately leading to lipid accumulation and apoptosis. These findings provide valuable insights into the ecological risks associated with MC-LR during the process of cyanobacterial resource utilization.

Deeper insight into the storage time of food waste on black soldier fly larvae growth and nutritive value: Interactions of substrate and gut microorganisms

Biological treatment of food waste (FW) by black soldier fly larvae (BSFL) is considered as an effective management strategy. The composition and concentrations of nutrients in FW change during its storage and transport period, which potentially affect the FW conversion and BSFL growth. The present study systematically investigated the effect of different storage times (i.e., 0-15 d) on FW characteristics and its substantial influence on the BSFL growth. Results showed that the highest larvae weight of 282 mg and the shortest growth time of 14 days were achieved at the group of FW stored for 15 days, but shorter storage time (i.e., 2-7 d) had adverse effect on BSFL growth. Short storage time (i.e., 2-4 d) improved protein content of BSFL biomass and prolonged storage time (i.e., 7-10 d) led to the accumulation of fat content. The changes of substrate characteristics and indigenous microorganisms via FW storage time were the main reasons for BSFL growth difference. Lactic acid (LA) accumulation (i.e., 19.84 g/L) in FW storage for 7 days significantly limited the BSFL growth, leading to lowest larvae weight. Both the substrate and BSFL gut contained same bacterial communities (e.g., Klebsiella and Proteus), which exhibited similar change trend with the prolonged storage time. The transfer of Clostridioides from substrate to BSFL gut promoted nutrients digestion and intestinal flora balance with the FW stored for 15 days. Pathogens (e.g., Acinetobacter) in BSFL gut feeding with FW storage time of 7 days led to the decreased digestive function, consistent with the lowest larvae weight. Overall, shorter storage time (i.e., 2-7 d) inhibited the BSFL digestive function and growth performance, while the balance of the substrate nutrients and intestinal flora promoted the BSFL growth when using the FW stored for 15 days.

Enhanced protein degradation by black soldier fly larvae (Hermetia illucens L.) and its gut microbes

Black soldier fly larvae (BSFL) can convert a variety of organic wastes into biomass, and its gut microbiota are involved in this process. However, the role of gut microbes in the nutrient metabolism of BSFL is unclear. In this study, germ-free BSFL (GF) and gnotobiotic BSFL (GB) were evaluated in a high-protein artificial diet model. We used 16S rDNA sequencing, ITS1 sequencing, and network analysis to study gut microbiota in BSFL that degrade proteins. The protein reduction rate of the GB BSFL group was significantly higher (increased by 73.44%) than that of the GF BSFL group. The activity of gut proteinases, such as trypsin and peptidase, in the GB group was significantly higher than the GF group. The abundances of different gut microbes, including Pseudomonas spp., Orbus spp. and Campylobacter spp., were strongly correlated with amino acid metabolic pathways. Dysgonomonas spp. were strongly correlated with protein digestion and absorption. Issatchenkia spp. had a strong correlation with pepsin activity. Campylobacter spp., Pediococcus spp. and Lactobacillus spp. were strongly correlated with trypsin activity. Lactobacillus spp. and Bacillus spp. were strongly correlated with peptidase activity. Gut microbes such as Issatchenkia spp. may promote the gut proteolytic enzyme activity of BSFL and improve the degradation rate of proteins. BSFL protein digestion and absorption involves gut microbiota that have a variety of functions. In BSFL the core gut microbiota help complete protein degradation. These results demonstrate that core gut microbes in BSFL are important in protein degradation.

Effects of salvaged cyanobacteria content on larval development and feedstock humification during black soldier fly larvae (Hermetia illucens) composting

Cyanobacteria salvage is widely used to deal with massive cyanobacterial blooms. Improper disposal of salvaged cyanobacteria would cause secondary pollution. Black soldier fly (Hermetia illucens) larvae (BSFL) can bio-convert organic wastes into larval biomass, which is rich in protein and lipid. This study evaluated the possibility of using BSFL composting for salvaged cyanobacteria treatment. Results showed that increasing salvaged cyanobacteria waste (CW) content (from 0 to 50%, dry weight basis) extended BSFL development time, e.g., BSFL fed with 50% CW needed 14 days more to finish development than Control (0% CW). The CW content (0-20%) in feeding substrates had no significant effect on BSFL body length and weight. Whereas further increase of CW content (from 20 to 50%) led to significant reductions in substrate-to-BSFL biomass conversion ratio, body size, body weight, and crude protein content of BSFL. Meanwhile, the presence of salvaged cyanobacteria in the feeding substrate reduced the degradation efficiency of feeding substrate. The dissolved organic matter (DOM) results demonstrated that the increased salvaged cyanobacteria content made it more difficult for BSFL to degrade the feeding substrate into simple organic matter and further into humic-like substances. Furthermore, salvaged cyanobacteria in feeding substrates affected the intestinal microbial community significantly. With 20% CW content in the feeding substrate, the relative abundance of Firmicutes decreased from 92.43 to 81.24%, while the relative abundance of Proteobacteria and Bacteroidetes increased from 4.10 to 2.93-8.75% and 7.51%, respectively. BSFL composting is feasible to convert salvaged cyanobacteria into insect biomass. However, the salvaged cyanobacteria content in the feeding substrate should be carefully controlled (e.g., less than 30%).

Toxic Effects of Industrial Flocculants Addition on Bioconversion of Black Soldier Fly Larvae (Hermetia illucens L.)

Simple Summary

The black soldier fly (BSF) is a saprophagous insect that has been applied to organic waste management while providing high-quality insect protein. Flocculants are widely present in organic wastes that could be treated by black soldier fly larvae (BSFL), such as food wastes, municipal sludge, and cyanobacteria sludge. This study investigated the effect of flocculants on bioconversion of BSFL. The results showed that the addition of flocculant affected the bioconversion efficiency and nutritional composition of BSFL. The relative abundance of bacterial genera related to lipid metabolism decreased with increasing flocculant concentrations while disease-related taxa increased in relative abundance. This study could serve as a reference for related research and applications in the future.

Abstract

Black soldier fly is a saprophagous insect that has been widely reported in recent years due to its excellent performance in bioremediation. Due to the widespread presence of flocculants in the organic waste treated by black soldier fly larvae, this study aimed to evaluate the potential impacts and risks of flocculant addition (a combination of poly aluminum chloride and polyacrylamide with the ratio of 50:1). Results showed that the growth and weight of BSFL in the high-exposure groups (≥200 mg/L) were inhibited. The bioaccumulation of aluminum (Al) in larvae was estimated, and the proportions of different Al forms in the frass from high to low were the residual state (41.38% to 67.92%), water-soluble state (16.88% to 37.03%), acid-soluble state (8.45% to 18.72%), and alkali-soluble state (3.38% to 5.14%). The relative abundance of bacterial genera related to lipid metabolism decreased with increasing flocculant concentrations while disease-related taxa increased in relative abundance. The results serve as a reference for subsequent research and application of the treatment of flocculant-contaminated waste by BSFL.