The gut and feed residue microbiota changing during the rearing of Hermetia illucens larvae

Intestinal microbial community well explain larval growth than feed types

Black soldier fly larvae (BSFL) are considered a sustainable ingredient in livestock feed. However, addressing issues related to feed substrate and intestinal microbiota is essential to ensure optimal larval development. The aim of this study was to assess and elucidate the contribution of substrate nutrients and intestinal microbes to protein and fat synthesis in BSFL. The results showed that larvae that were fed high-quality feed (chicken feed) had high fat biomass, while larvae that were fed medium-quality feed (wheat bran) had high protein biomass. These results indicate that the original nutritional content of the feed cannot fully explain larval growth and nutrient utilization. However, the phenomenon could be explained by the functional metabolism of intestinal microbes. Chicken feed enhanced the fatty acid metabolism of middle intestine microorganisms in larvae within 0-7 days. This process facilitated larval fat synthesis. In contrast, wheat bran stimulated the amino acid metabolism in posterior intestine microorganisms in larvae within 4-7 days, leading to better protein synthesis. The findings of this study highlight the importance of the microbial functional potential in the intestine in regulating protein and lipid synthesis in BSFL, which is also influenced by the type of feed. In conclusion, our study suggests that both feed type and intestinal microbes play a crucial role in efficiently converting organic waste into high-quality insect protein and fat. Additionally, a mixed culture of chicken feed and wheat bran was found to be effective in promoting larval biomass while reducing feed costs. KEY POINTS: • Intestinal microbes explain BSFL growth better than feed substrates. • Chicken feed promotes fatty acid synthesis in the middle intestine • Wheat bran promotes amino acid synthesis in the posterior intestine.

Microplastics in the diet of Hermetia illucens: Implications for development and midgut bacterial and fungal microbiota

In a world with a population exceeding 8 billion people and continuing to grow, pollution from food and plastic waste is causing long-term issues in ecosystems. Potential solutions may be found by exploiting insect-based bioconversion. In this context, we investigated the impact of polyvinyl chloride microparticles (PVC-MPs) on the development of Hermetia illucens (black soldier fly; BSF) and its midgut bacterial and fungal microbiota. The impact of PVC-MPs was evaluated feeding BSF larvae with a PVC-MPs-supplemented diet. The larvae exposed to different PVC-MPs concentrations (2.5%, 5%, 10% and 20% w/w) developed into adults with no significant increase in pupal mortality. Faster development and smaller pupae were observed when 20% PVC-MPs was provided. The BSF larvae ingest PVC-MPs, resulting in a reduction in MPs size. Larvae exposed to PVC-MPs did not exhibit differences in gut morphology. Regarding the impact of PVC-MPs on the structure of both bacterial and fungal communities, the overall alpha- and beta-diversity did not exhibit significant changes. However, the presence of PVC-MPs significantly affected the relative abundances of Enterobacteriaceae and Paenibacillaceae among the bacteria and of Dipodascaceae and Plectospharellaceae among the fungi (including yeast and filamentous life forms), suggesting that PVC-MP contamination has a taxa-dependent impact. These results indicate that BSF larvae can tolerate PVC-MPs in their diet, supporting the potential use of these insects in organic waste management, even in the presence of high levels of PVC-MP contamination.

Treatment of landfill leachate by black soldier fly (Hermetia illucens L.) larvae and the changes of intestinal microbial community

Black soldier fly larvae (BSFL) (Hermetia illucens) are commonly used to treat organic waste. This work aims to evaluate the transformation effect, heavy metal migration, and alterations in the gut microbiota of BSFL in addition to treating landfill leachate (LL) with BSFL. We found that BSFL may grow in various landfill leachate concentrations without obvious toxicity and growth inhibition. In addition, the results indicated a significant increase in the content of ammonia nitrogen and the activity of urease and β-glucosidase (β-GC) in LL, increased from 2570.17 mg/L to 5853.67 mg/L, 1859.17 mg/(g·d) to 517,177.98 mg/(g·d), 313.73 μg/(g·h) to 441.91 μg/(g·h) respectively. Conversely, the content of total nitrogen (TN) and total organic carbon (TOC) decreased in LL, decreasing by 31.24% and 29.45% respectively. Heavy metals are accumulated in the leachate by the BSFL to differing degrees, the descending sequence of accumulation is Cd > As > Cu > Cr. As dropped by 26.0%, Cd increased by 22.6%, Cu reduced by 5.23%, and Cr increased by 317.1% in the remaining matrix. The concentration of heavy metals satisfies the organic fertilizers' limit index (NY/T1978). The diversity of intestinal microorganisms in BSFL decreased, from 2819 OTUs to 2338 OTUs, with Providencia and Morganella emerging as the core flora. The gene abundance of nitrogen metabolism in the microbiota increased significantly. The TOC, β-GC, and Copper (Cu) content in BSFL correlated significantly with the gut microbiota. In Summary, this study revealed the treatment effect of BSFL on LL, the migration of heavy metals, and changes in the intestinal microorganisms of BSFL. The content of heavy metals in BSFL was found to be much lower than the upper limit of feed protein raw materials, demonstrating that BSFL is a sustainable method to treat LL.

Microbial dynamics and vertical transmission of Escherichia coli across consecutive life stages of the black soldier fly (Hermetia illucens)

BACKGROUND

The black soldier fly (BSF, Hermetia illucens L.) is one of the most promising insects for bioconversion of organic waste, which often carry a high microbial load with potential foodborne pathogens. Although horizontal transmission (from rearing substrate to larvae) has been extensively studied, less is known about vertical transmission of microorganisms, and particularly of foodborne pathogens, across different BSF life stages.

RESULTS

This study investigated the microbial dynamics and vertical transmission of Escherichia coli across different life stages (larvae, prepupae, pupae and adults) of one BSF life cycle and its associated substrate (chicken feed) and frass, based on a combination of general microbial counts (based on culture-dependent techniques) and the bacterial community composition (based on 16S rRNA gene sequencing). Multiple interactions between the microbiota of the substrate, frass and BSF larvae were affirmed. The larvae showed relative consistency among both the microbial counts and bacterial community composition. Diversification of the bacterial communities started during the pupal stage, while most notable changes of the microbial counts and bacterial community compositions occurred during metamorphosis to adults. Furthermore, vertical transmission of E. coli was investigated after substrate inoculation with approximately 7.0 log cfu/g of kanamycin-resistant E. coli, and monitoring E. coli counts from larval to adult stage. Although the frass still contained substantial levels of E. coli (> 4.5 log cfu/g) and E. coli was taken up by the larvae, limited vertical transmission of E. coli was observed with a decreasing trend until the prepupal stage. E. coli counts were below the detection limit (1.0 log cfu/g) for all BSF samples from the end of the pupal stage and the adult stage. Additionally, substrate inoculation of E. coli did not have a substantial impact on the bacterial community composition of the substrate, frass or different BSF life stages.

CONCLUSIONS

The fluctuating microbial counts and bacterial community composition underscored the dynamic character of the microbiota of BSF life stages. Additionally, vertical transmission throughout one BSF life cycle was not observed for E. coli. Hence, these findings paved the way for future case studies on vertical transmission of foodborne pathogens across consecutive BSF life stages or other insect species.

Evaluation of the Microbial Quality of Hermetia illucens Larvae for Animal Feed and Human Consumption: Study of Different Type of Rearing Substrates

In the context of climate change and depletion of natural resources, meeting the growing demand for animal feed and human food through sufficient, nutritious, safe, and affordable sources of protein is becoming a priority. The use of Hermetia illucens, the black soldier fly (BSF), has emerged as a strategy to enhance the circularity of the agri-food chain, but its microbiological safety remains a concern. The aim of the present study was to systematically review available data on the microbiological quality of BSF and to investigate the impact of using four different rearing substrates including classic options allowed by the EU regulation (cereals, fruits, vegetables) and options not allowed by EU regulations regarding vegetable agri-food (co-products, food at shelf life, and meat). A total of 13 studies were collected and synthesized, including 910 sample results, while 102 new sample results were collected from the present experiments in three farms. Both datasets combined revealed a high level of contamination of larvae, potentially transmitted through the substrate. The main pathogenic bacteria identified were Bacillus cereus, Clostridium perfringens, Cronobacter spp., Escherichia coli, Salmonella spp., and Staphylococcus aureus coagulase-positive, while Campylobacter spp. and Listeria monocytogenes were not detected. Any of these four substrates were excluded for their use in insect rearing; however, safety concerns were confirmed and must be managed by the operators of the sector using microbial inactivation treatment after the harvest of the larvae in order to propose safe products for the market. The results obtained will guide the definition of the control criteria and optimize the following manufacturing steps.

Using kin discrimination to construct synthetic microbial communities of Bacillus subtilis strains impacts the growth of black soldier fly larvae

Using synthetic microbial communities to promote host growth is an effective approach. However, the construction of such communities lacks theoretical guidance. Kin discrimination is an effective means by which strains can recognize themselves from non-self, and construct competitive microbial communities to produce more secondary metabolites. However, the construction of cooperative communities benefits from the widespread use of beneficial microorganisms. We used kin discrimination to construct synthetic communities (SCs) comprising 13 Bacillus subtilis strains from the surface and gut of black soldier fly (BSF) larvae. We assessed larval growth promotion in a pigeon manure system and found that the synthetic community comprising 4 strains (SC 4) had the most profound effect. Genomic analyses of these 4 strains revealed that their complementary functional genes underpinned the robust functionality of the cooperative synthetic community, highlighting the importance of strain diversity. After analyzing the bacterial composition of BSF larvae and the pigeon manure substrate, we observed that SC 4 altered the bacterial abundance in both the larval gut and pigeon manure. This also influenced microbial metabolic functions and co-occurrence network complexity. Kin discrimination facilitates the rapid construction of synthetic communities. The positive effects of SC 4 on larval weight gain resulted from the functional redundancy and complementarity among the strains. Furthermore, SC 4 may enhance larval growth by inducing shifts in the bacterial composition of the larval gut and pigeon manure. This elucidated how the SC promoted larval growth by regulating bacterial composition and provided theoretical guidance for the construction of SCs.

Garden fruit chafer (Pachnoda sinuata L.) accelerates recycling and bioremediation of animal waste

Bioconversion of livestock wastes using insect larvae represents an emerging and effective strategy for waste management. However, knowledge on the role of the garden fruit chafer (Pachnoda sinuataL.) in waste recycling and influence on the diversity ofmicrobial community infrass fertilizeris limited. Here, we determined whether and to what extent the conversion of cattle dung into insect frass fertilizer byP. sinuatainfluences the frass' microbial community and its associated antibiotic resistance genes abundance. Pachnoda sinuata larvae were used to valorise cattle dung into frass fertilizer; samples were collected weekly to determine the composition of bacteria and fungi, and antibiotic resistant genes using molecular tools. Results revealed that bioconversion of cattle dung byP. sinuatalarvae significantly increased the richness of beneficial bacteria in the frass fertilizer by 2.5-folds within 28 days, but fungal richness did not vary during the study. Treatment of cattle dung withP. sinuatalarvae caused 2 - 3-folds decrease in the genes conferring resistance to commonly used antibiotics such as aminoglycoside, diaminopyrimidine, multidrug, sulfonamide and tetracycline within 14 days. Furthermore, the recycling cattle dung using considerably reduced the abundance of mobile genetic elements known to play critical roles in the horizontal transfer of antibiotic resistance genes between organisms. This studyhighlights the efficiency ofsaprohytic insects in recycling animal manure and suppressing manure-borne pathogens in the organic fertilizer products, opening new market opportunities for innovative and safe bio-based products and achieving efficient resource utilization in a circular and green economy.

Deciphering the functional diversity of the gut microbiota of the black soldier fly (Hermetia illucens): recent advances and future challenges

Bioconversion using insects is a promising strategy to convert organic waste (catering leftovers, harvest waste, food processing byproducts, etc.) into biomass that can be used for multiple applications, turned into high added-value products, and address environmental, societal and economic concerns. Due to its ability to feed on a tremendous variety of organic wastes, the black soldier fly (Hermetia illucens) has recently emerged as a promising insect for bioconversion of organic wastes on an industrial scale. A growing number of studies have highlighted the pivotal role of the gut microbiota in the performance and health of this insect species. This review aims to provide a critical overview of current knowledge regarding the functional diversity of the gut microbiota of H. illucens, highlighting its importance for bioconversion, food safety and the development of new biotechnological tools. After providing an overview of the different strategies that have been used to outline the microbial communities of H. illucens, we discuss the diversity of these gut microbes and the beneficial services they can provide to their insect host. Emphasis is placed on technical strategies and aspects of host biology that require special attention in the near future of research. We also argue that the singular digestive capabilities and complex gut microbiota of H. illucens make this insect species a valuable model for addressing fundamental questions regarding the interactions that insects have evolved with microorganisms. By proposing new avenues of research, this review aims to stimulate research on the microbiota of a promising insect to address the challenges of bioconversion, but also fundamental questions regarding bacterial symbiosis in insects.

Microbiota is structured by gut regions, life stage, and diet in the Black Soldier Fly (Hermetia illucens)

The larvae of the Black Soldier Fly (Hermetia illucens) provide numerous ecological benefits, leading to significant commercial advancements. These benefits include the bioconversion of low-value waste into high-value feed and soil amendments. Understanding how the bacterial and eukaryotic microbiota communities affect host performance becomes vital for the optimization and specialization of industrial-scale rearing. This study investigates H. illucens-associated microbiota taxonomic composition and dynamics across the developmental cycle (eggs, neonates, larvae, prepupae, and imago X0 to second generation X1) when reared on two substrates: (i) plant-based (Housefly Gainesville diet) and (ii) animal-based (poultry hatchery waste). By using the 16S gene amplicon metataxonomic approach, we found that the results revealed that bacterial microbiota inherited from parents reared on a different substrate may have induced dysbiosis in the progeny. Specifically, the interaction networks of individuals reared on hatchery waste showed a high prevalence of negative interactions and low connectivity. Proteobacteria (39-92%), Firmicutes (4-39%), Bacteroidota (1-38%), and Actinobacteria (1-33%). In animal feed-reared individuals, Firmicutes reached the highest relative abundance (10-80%), followed by Proteobacteria (6-55%), Actinobacteria (1-31%), and Bacteroidota (0-22%). The rearing substrate was the main driver of microbiota composition, while the developmental stage influenced only the whole individual's bacterial microbiota composition. Gut regions were associated with distinct bacterial composition and richness, with diversity decreasing along the digestive tract. For the first time, microeukaryotes of the microbiota other than Fungi were investigated using 18S genetic marker amplicon sequencing with novel blocking primers specific to the Black Soldier Fly. Microeukaryotes are a neglected part of multitrophic microbiota communities that can have similar effects on their hosts as bacterial microbiota. Microeukaryotes from seven orders were identified in black soldier flies, including potential pathogens (e.g., Aplicomplexa group). Nucletmycea were the dominant class throughout development, followed by Holozoa and Stramenophiles. The eukaryote microbiota was structured by developmental stages but not by gut regions. Insights from this study are a stepping stone toward the microbiological optimization of black soldier flies for industrial rearing, highlighting how a synthetic microbiota assembly should be tailored to the rearing environment of the larvae at a targeted developmental stage.

Insects as food and medicine: a sustainable solution for global health and environmental challenges

Insects are a significant source of food for millions of people worldwide. Since ancient times, insects in medicine have been contributing to the treatment of diseases in humans and animals. Compared to conventional animal farming, the production of insects for food and feed generates significantly less greenhouse gas emissions and uses considerably less land. Edible insects provide many ecosystem services, including pollination, environmental health monitoring, and the decomposition of organic waste materials. Some wild edible insects are pests of cash crops. Thus, harvesting and consuming edible insect pests as food and utilizing them for therapeutic purposes could be a significant progress in the biological control of insect pests. Our review discusses the contribution of edible insects to food and nutritional security. It highlights therapeutic uses of insects and recommends ways to ensure a sustainable insect diet. We stress that the design and implementation of guidelines for producing, harvesting, processing, and consuming edible insects must be prioritized to ensure safe and sustainable use.

Changes in Bacterial Community Structure Across the Different Life Stages of Black Soldier Fly (Hermetia illucens)

The digestive capacity of organic compounds by the black soldier fly (BSF, Hermetia illucens, Diptera: Stratiomyidae, Linnaeus, 1758) is known to rely on complex larva-microbiota interactions. Although insect development is known to be a driver of changes of bacterial communities, the fluctuations along BSF life cycle in terms of composition and diversity of bacterial communities are still unknown. In this work, we used a metabarcoding approach to explore the differences in bacterial diversity along all four BSF developmental stages: eggs, larvae, pupae, and adult. We detected not only significant differences in bacterial community composition and species richness along the development of BSF, but also nine prevalent amplicon single variants (ASVs) forming the core microbiota. Out of the 2010 ASVs identified, 160 were significantly more abundant in one of the life stages. Moreover, using PICRUSt2, we inferred 27 potential metabolic pathways differentially used among the BSF life cycle. This distribution of metabolic pathways was congruent with the bacterial taxonomic distribution among life stages, demonstrating that the functional requirements of each phase of development are drivers of bacterial composition and diversity. This study provides a better understanding of the different metabolic processes occurring during BSF development and their links to changes in bacterial taxa. This information has important implications for improving bio-waste processing in such an economically important insect species.

Meta-analysis of larvae of the black soldier fly (Hermetia illucens) microbiota based on 16S rRNA gene amplicon sequencing

Black soldier fly larvae (BSFL) belong to the most widely reared insects as an alternative protein source at industrial scale. Bacteria in the larval gut can provide benefits for the animal, though some bacteria can also be pathogenic for the insect. Accurate characterization of the BSFL microbiota is important for the production of BSFL in terms of yield and microbiological safety. In this study, 16S ribosomal RNA gene sequence data sets from 11 studies were re-analysed to gain better insights in the BSFL gut microbiota, potential factors that influence their composition, and differences between the gut and the whole larvae microbiota. A core gut microbiota was found consisting of members of Enterococcus, Klebsiella, Morganella, Providencia, and Scrofimicrobium. Further, the factors 'Study', 'Age' and 'Feed' (i.e. rearing substrate of the larvae) significantly affected the microbiota gut composition. When compared to whole larvae, a significantly lower diversity was found for gut samples, suggesting that the larvae harboured additional microbes on their cuticle or in the insect body. Universal choices in insect sample type, primer selection and bio-informatics analysis pipeline can strengthen future meta-analyses and improve our understanding of the BSFL gut microbiota towards the optimization of insect rearing conditions and substrates.

Dynamics of the intestinal bacterial community in black soldier fly larval guts and its influence on insect growth and development

Black soldier fly (BSF), Hermetia illucens (Diptera: Stratiomyidae), is a prominent insect for the bioconversion of various organic wastes. As a saprotrophic insect, the BSF inhabits microbe-rich environments. However, the influences of the intestinal microorganisms on BSF growth and development are not very clear. In this study, the dynamics of the intestinal bacterial community of BSF larvae (BSFL) were analyzed using pyrosequencing. Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria were the most prevalent bacterial phyla in the intestines of all larval instars. The dynamic changes in bacterial community compositions among different larval instars were striking at the genus level. Klebsiella, Clostridium, Providencia, and Dysgonomonas were the relatively most abundant bacteria in the 1st- to 4th-instar BSFL, respectively. Dysgonomonas and Providencia also dominated the 5th- and 6th-instar larvae, at ratios of 31.1% and 47.2%, respectively. In total, 148 bacterial strains affiliated with 20 genera were isolated on different media under aerobic and anaerobic conditions. Among them, 6 bacteria, BSF1-BSF6, were selected for further study. The inoculation of the 6 isolates independently into germ-free BSFL feeding on an artificial diet showed that all the bacteria, except BSF4, significantly promoted BSF growth and development compared with the germ-free control. Citrobacter, Dysgonomonas, Klebsiella, Ochrobactrum, and Providencia promoted BSF development significantly by increasing the weight gains of larvae and pupae, as well as increasing the prepupae and eclosion rates. In addition, Citrobacter, Klebsiella and Providencia shortened the BSF life cycle significantly. The results illustrate the promotive effects of intestinal bacteria on BSF growth and development.

Diet Fermentation Leads to Microbial Adaptation in Black Soldier Fly (Hermetia illucens; Linnaeus, 1758) Larvae Reared on Palm Oil Side Streams

Insects offer a promising alternative source of protein to mitigate the environmental consequences of conventional livestock farming. Larvae of the black soldier fly (Hermetia illucens; Linnaeus, 1758) efficiently convert a variety of organic side streams and residues into valuable proteins, lipids, and chitin. Here, we evaluated the suitability of two palm oil industry side streams—empty fruit bunches (EFB) and palm kernel meal (PKM)—as larval feed, and their impact on the larval gut microbiome. Among 69 fungal species we screened, Marasmius palmivorus, Irpex consors, and Bjerkandera adusta achieved the fastest growth and lignin degradation, so these fungi were used for the pretreatment of 7:3 mixtures of EFB and PKM. Larvae reared on the mixture pretreated with B. adusta (BAD) developed significantly more quickly and reached a higher final weight than those reared on the other pretreatments or the non-fermented reference (NFR). Amplicon sequencing of the BAD and NFR groups revealed major differences in the larval gut microbiome. The NFR group was dominated by facultatively anaerobic Enterobacteriaceae (typical of H. illucens larvae) whereas the BAD group favored obligately anaerobic, cellulolytic bacteria (Ruminococcaceae and Lachnospiraceae). We hypothesize that fungal lignin degradation led to an accumulation of mycelia and subsequent cellulolytic breakdown of fiber residues, thus improving substrate digestibility.

Isolation of Hermetia illucens larvae core gut microbiota by two different cultivation strategies

Hermetia illucens larvae (black soldier fly larvae, BSFL) convert efficiently organic waste to high quality biomass. To gain knowledge on the specific functions of gut microbes in this process it is a prerequisite to culture members of the core gut microbiota. Two different cultivation strategies were applied here for this purpose, a dilution-to-extinction cultivation and direct plating using six different media to culture aerobic heterotrophic bacteria. A total of 341 isolates were obtained by the dilution-to-extinction cultivation and 138 isolates by direct plating from guts of BSFL reared on chicken feed. Bacterial isolates were phylogenetically identified at the genus level by 16S rRNA gene sequencing (phylotyping) and differentiated at the strain level by genomic fingerprinting (genotyping). The main proportion of isolates was assigned to Proteobacteria, Firmicutes (Bacilli), and Actinobacteria. Predominant genera discussed in literature as member of a potential BSFL core gut microbiota, Providencia, Proteus, Morganella, Enterococcus, Bacillus, and members of the family Enterobacteriaceae, were isolated. A high intra-phylotype diversity was obtained by genomic fingerprinting which was especially enhanced by the dilution-to-extinction cultivation. This study showed that the application of different cultivation strategies including a dilution-to-extinction cultivation helps to culture a higher diversity of the BSFL gut microbiota and that genomic fingerprinting gives a better picture on the genetic diversity of cultured bacteria which cannot be covered by a 16S rRNA gene sequence based identification alone.

Modulation of Atlantic salmon (Salmo salar) gut microbiota composition and predicted metabolic capacity by feeding diets with processed black soldier fly (Hermetia illucens) larvae meals and fractions

BACKGROUND

Black soldier fly (Hermetia illucens) is a promising insect species to use as a novel ingredient in fish feeds. Black soldier fly larvae consists of three major fractions, namely protein, lipid, and exoskeleton. These fractions contain bioactive compounds that can modulate the gut microbiota in fish such as antimicrobial peptides, lauric acid, and chitin. However, it is not certain how, or which fractions of black solider fly would affect gut microbiota in fish. In the present study, black soldier fly larvae were processed into three different meals (full-fat, defatted and de-chitinized) and two fractions (oil and exoskeleton), and included in diets for Atlantic salmon (Salmo salar). Atlantic salmon pre-smolts were fed with these diets in comparison with a commercial-like control diet for eight weeks to investigate the effects of insect meals and fractions on the composition and predicted metabolic capacity of gut microbiota. The gut microbiota was profiled by 16S rRNA gene sequencing, and the predicted metabolic capacities of gut microbiota were determined using genome-scale metabolic models.

RESULTS

The inclusion of insect meals and fractions decreased abundance of Proteobacteria and increased abundance of Firmicutes in salmon gut. The diets that contained insect chitin, i.e., insect meals or exoskeleton diets, increased abundance of chitinolytic bacteria including lactic acid bacteria and Actinomyces in salmon gut, with fish fed full-fat meal diet showing the highest abundances. The diets that contained insect lipids, i.e., insect meals and oil diets enriched Bacillaceae in fish gut. The fish fed diets containing full-fat insect meal had a unique gut microbiota composition dominated by beneficial lactic acid bacteria and Actinomyces, and showed a predicted increase in mucin degradation compared to the other diets.

CONCLUSIONS

The present results showed that the dietary inclusion of insect meals and fractions can differently modulate the composition and predicted metabolic capacity of gut microbiota in Atlantic salmon pre-smolts. The use of full-fat black soldier fly larvae meal in diets for salmon is more favorable for beneficial modulation of gut microbiota than larvae processed by separation of lipid or exoskeleton fractions.

A Preliminary Comparison on Faecal Microbiomes of Free-Ranging Large Baleen (Balaenoptera musculus, B. physalus, B. borealis) and Toothed (Physeter macrocephalus) Whales

Large baleen and toothed whales play crucial ecological roles in oceans; nonetheless, very little is known about their intestinal microbiomes. Based on striking differences in natural history and thus in feeding behaviours, it can be expected that intestinal microbiomes of large baleen whales and toothed whales are different. To test this hypothesis, the phylogenetic composition of faecal microbiomes was investigated by a 16S rRNA gene amplicon sequence-based approach for Bacteria and Archaea. Faecal samples from free-ranging large whales collected off the Azores Archipelago (Portugal) were used, comprising 13 individual baleen whales (one sei, two blue and ten fin whales) and four sperm whales. The phylogenetic composition of the Bacteria faecal microbiomes of baleen and toothed whales showed no significant differences at the phylum level. However, significant differences were detected at the family and genus levels. Most abundant phyla were Firmicutes, Bacteroidetes, Proteobacteria, Tenericutes and Spirochaeta. Few highly abundant bacterial genera were identified as key taxa with a high contribution to differences among baleen and toothed whales microbiomes. Only few archaeal sequences were detected, primarily Methanomassiliicoccales representing potential methanogenic Archaea. This is the first study that directly compares the faecal bacterial and archaeal microbiomes of free-ranging baleen and toothed whales which represent the two parvorders of Cetacea which members are fully aquatic large mammals which were evolutionary split millions of years ago.

Directional Changes in the Intestinal Bacterial Community in Black Soldier Fly (Hermetia illucens) Larvae

Black soldier fly (BSF) larvae, Hermetia illucens (Diptera: Stratiomyidae) have emerged as an efficient system for the bioconversion of organic waste. Intestinal microorganisms are involved in several insect functions, including the development, nutrition, and physiology of the host. In order to transform the intestinal bacterial community of BSF directionally, six different potential functional strains (Lysinibacillus sphaericus, Proteus mirabilis, Citrobacter freundii, Pseudocitrobacter faecalis, Pseudocitrobacter anthropi, and Enterococcus faecalis) were added to aseptic food waste, and aseptic food waste was used without inoculants as a blank control to evaluate the changes in the intestinal microbiota of BSF under artificial intervention conditions. These six strains (which were isolated from the larval intestinal tract in selective media and then identified and screened) may be considered responsible for the functional characteristics of larvae. The results imply that the increase in the abundance of Lysinibacillus in the experimental group that was exposed to Lysinibacillus sphaericus was significantly different to the other groups (p < 0.05). The results revealed that it is feasible to transform the intestinal microbiota of BSF directionally; there are differences in the proliferation of different strains in the intestine of BSF.

A Molecular Survey of Bacterial Species in the Guts of Black Soldier Fly Larvae (Hermetia illucens) Reared on Two Urban Organic Waste Streams in Kenya

Globally, the expansion of livestock and fisheries production is severely constrained due to the increasing costs and ecological footprint of feed constituents. The utilization of black soldier fly (BSF) as an alternative protein ingredient to fishmeal and soybean in animal feed has been widely documented. The black soldier fly larvae (BSFL) used are known to voraciously feed and grow in contaminated organic wastes. Thus, several concerns about their safety for inclusion into animal feed remain largely unaddressed. This study evaluated both culture-dependent sequence-based and 16S rDNA amplification analysis to isolate and identify bacterial species associated with BSFL fed on chicken manure (CM) and kitchen waste (KW). The bacteria species from the CM and KW were also isolated and investigated. Results from the culture-dependent isolation strategies revealed that Providencia sp. was the most dominant bacterial species detected from the guts of BSFL reared on CM and KW. Morganella sp. and Brevibacterium sp. were detected in CM, while Staphylococcus sp. and Bordetella sp. were specific to KW. However, metagenomic studies showed that Providencia and Bordetella were the dominant genera observed in BSFL gut and processed waste substrates. Pseudomonas and Comamonas were recorded in the raw waste substrates. The diversity of bacterial genera recorded from the fresh rearing substrates was significantly higher compared to the diversity observed in the gut of the BSFL and BSF frass (leftovers of the rearing substrates). These findings demonstrate that the presence and abundance of microbiota in BSFL and their associated waste vary considerably. However, the presence of clinically pathogenic strains of bacteria in the gut of BSFL fed both substrates highlight the biosafety risk of potential vertical transmission that might occur, if appropriate pre-and-postharvest measures are not enforced.

Culture-Independent and Culture-Dependent Characterization of the Black Soldier Fly Gut Microbiome Reveals a Large Proportion of Culturable Bacteria with Potential for Industrial Applications

Black soldier fly larvae (BSFL) are fast-growing, resilient insects that can break down a variety of organic substrates and convert them into valuable proteins and lipids for applications in the feed industry. Decomposition is mediated by an abundant and versatile gut microbiome, which has been studied for more than a decade. However, little is known about the phylogeny, properties and functions of bacterial isolates from the BSFL gut. We therefore characterized the BSFL gut microbiome in detail, evaluating bacterial diversity by culture-dependent methods and amplicon sequencing of the 16S rRNA gene. Redundant strains were identified by genomic fingerprinting and 105 non-redundant isolates were then tested for their ability to inhibit pathogens. We cultivated representatives of 26 genera, covering 47% of the families and 33% of the genera detected by amplicon sequencing. Among these isolates, we found several representatives of the most abundant genera: Morganella, Enterococcus, Proteus and Providencia. We also isolated diverse members of the less-abundant phylum Actinobacteria, and a novel genus of the order Clostridiales. We found that 15 of the isolates inhibited at least one of the tested pathogens, suggesting a role in helping to prevent colonization by pathogens in the gut. The resulting culture collection of unique BSFL gut bacteria provides a promising resource for multiple industrial applications.

Black Soldier Fly Larvae Can Effectively Degrade Oxytetracycline Bacterial Residue by Means of the Gut Bacterial Community

Antibiotic bacterial residue is a unique hazardous waste, and its safe and effective disposal has always been a concern of pharmaceutical enterprises. This report presents the effective treatment of hazardous waste-antibiotic bacterial residue-by black soldier fly larvae (larvae), oxytetracycline bacterial residue (OBR), and soya meal with mass ratios of 0:1 (soya), 1:20 (OBRlow), and 1:2 (OBRhigh), which were used as substrates for larval bioconversion. Degradation of OBR and oxytetracycline, the bacterial community, the incidence of antibiotic resistance genes (ARGs) and the bacterial function in the gut were examined. When the larvae were harvested, 70.8, 59.3, and 54.5% of the substrates had been consumed for soya, OBRlow and OBRhigh; 65.9 and 63.3% of the oxytetracycline was degraded effectively in OBRlow and OBRhigh, respectively. The larval bacterial communities were affected by OBR, abundant and various ARGs were discovered in the gut, and metabolism was the major predicted function of the gut. These findings show that OBR can be digested and converted by larvae with gut bacteria, and the larvae can be used as a bioremediation tool for the treatment of hazardous waste. Finally, the abundant ARGs in the gut deserve further attention and consideration in environmental health risk assessments.

Isolation and Identification of Dominant Bacteria From Black Soldier Fly Larvae (Hermetia illucens) Envisaging Practical Applications

This study aimed to establish a representative strain collection of dominant aerobic bacteria from black soldier fly larvae (Hermetia illucens, BSFL). The larvae were fed either chicken feed or fiber-rich substrates to obtain a collection of BSFL-associated microorganisms. Via an approach based on only considering the highest serial dilutions of BSFL extract (to select for the most abundant strains), a total of 172 bacteria were isolated. Identification of these isolates revealed that all bacteria belonged to either the Proteobacteria (66.3%), the Firmicutes (30.2%), the Bacteroidetes (2.9%) or the Actinobacteria (0.6%). Twelve genera were collected, with the most abundantly present ones (i.e., minimally present in at least three rearing cycles) being Enterococcus (29.1%), Escherichia (22.1%), Klebsiella (19.8%), Providencia (11.6%), Enterobacter (7.6%), and Morganella (4.1%). Our collection of dominant bacteria reflects largely the bacterial profiles of BSFL already described in literature with respect to the most important phyla and genera in the gut, but some differences can be noticed depending on substrate, biotic and abiotic factors. Furthermore, this bacterial collection will be the starting point to improve in vitro digestion models for BSFL, to develop mock communities and to find symbionts that can be added during rearing cycles to enhance the larval performances, after functional characterization of the isolates, for instance with respect to enzymatic potential.

Cottonseed Press Cake as a Potential Diet for Industrially Farmed Black Soldier Fly Larvae Triggers Adaptations of Their Bacterial and Fungal Gut Microbiota

Black soldier fly larvae (Hermetia illucens, Diptera: Stratiomyidae) are used for the bioconversion of organic side products into valuable compounds such as proteins, lipids and chitin. However, the economic competitiveness of farmed insects compared to conventional protein production systems in agriculture and aquaculture depends on the availability of large quantities of inexpensive insect feed. Cottonseed press cake (CPC) is a side-stream of cotton production that is rich in proteins and lipids but unsuitable as feed for several farmed animals, except ruminants, due to the presence of the anti-nutritional sesquiterpenoid gossypol. Here, we tested CPC as a feed for black soldier fly larvae and studied the impact of this diet on the gut microbiome. Larvae reared on CPC developed normally and even showed a shorter life-cycle, but were smaller at the end of larval development than control larvae reared on chicken feed. The adaptability of the larvae to different diets is mediated by their versatile gut microbiome, which facilitates digestion and detoxification. We therefore used amplicon sequencing to analyze the bacterial and fungal communities associated with larvae reared on each diet, revealing differences between the larval guts and frass (residual feed substrate) as well as differences between the two diet groups. For example, Actinomycetaceae and Aspergillaceae were significantly enriched in guts of the CPC diet group and may help to metabolize compounds such as gossypol. Potentially probiotic yeasts and beneficial Enterobacteriaceae, which presumably belong to the core microbiota, were detected in high relative abundance in the gut and frass, indicating a functional role of these microbes, especially the protection against pathogens. We conclude that CPC may be suitable as an inexpensive and environmentally sustainable feed for the industrial rearing of black soldier flies.

Intestinal microbiota and functional characteristics of black soldier fly larvae (Hermetia illucens)

Purpose

Black soldier fly transforms organic waste into insect protein and fat, which makes it valuable for ecological utilization. This process is associated with the intestinal microbiota. This research was developed to determine the type and functional characteristics of intestinal microbiota present in black soldier fly larvae.

Methods

In this research, metagenomics has been used to study black soldier fly larvae gut bacteria, which involves the high abundance of the gut microbe advantage bacterium group, the impact, and the physiological functions of the microbiota. Furthermore, intestinal bacteria and their related functions were investigated by bioinformatics analysis to evaluate potential microbial strains that may be used to improve feed utilization efficiency in factory farming.

Result

The results showed that black soldier fly larvae’s intestine contains more than 11,000 bacteria. The high relative abundance of group W (larvae fed with 75% wheat bran and 25% soybean powder) may promote feed utilization efficiency, whereas high relative abundance of group T microbiota (larvae fed with 75% wheat bran and 25% soybean powder supplemented with 1% tetracycline) may play an important role in black soldier fly larvae survival.

Conclusion

The gut bacteria in black soldier fly larvae were involved in polysaccharide biosynthesis and metabolism, translation, membrane transport, energy metabolism, cytoskeleton, extracellular structures, inorganic ion transport and metabolism, nucleotide metabolism, and coenzyme transport physiological processes. The 35 significant differential microbes in group W may have a positive impact on feed utilization and physiological process.

Occurrence of Antibiotic Resistance Genes in Hermetia illucens Larvae Fed Coffee Silverskin Enriched with Schizochytrium limacinum or Isochrysis galbana Microalgae

Hermetia illucens larvae are among the most promising insects for use as food or feed ingredients due to their ability to convert organic waste into biomass with high-quality proteins. In this novel food or feed source, the absence of antibiotic-resistant bacteria and their antibiotic resistance (AR) genes, which could be horizontally transferred to animal or human pathogens through the food chain, must be guaranteed. This study was conducted to enhance the extremely scarce knowledge on the occurrence of AR genes conferring resistance to the main classes of antibiotics in a rearing chain of H. illucens larvae and how they were affected by rearing substrates based on coffee silverskin supplemented with increasing percentages of Schizochytrium limacinum or Isochrysis galbana microalgae. Overall, the PCR and nested PCR assays showed a high prevalence of tetracycline resistance genes. No significant effect of rearing substrates on the distribution of the AR genes in the H. illucens larvae was observed. In contrast, the frass samples were characterized by a significant accumulation of AR genes, and this phenomenon was particularly evident for the samples collected after rearing H. illucens larvae on substrates supplemented with high percentages (>20%) of I. galbana. The latter finding indicates potential safety concerns in reusing frass in agriculture.

Impact of Processed Food (Canteen and Oil Wastes) on the Development of Black Soldier Fly (Hermetia illucens) Larvae and Their Gut Microbiome Functions

Canteens represent an essential food supply hub for educational institutions, companies, and business parks. Many people in these locations rely on a guaranteed service with consistent quality. It is an ongoing challenge to satisfy the demand for sufficient serving numbers, portion sizes, and menu variations to cover food intolerances and different palates of customers. However, overestimating this demand or fluctuating quality of dishes leads to an inevitable loss of unconsumed food due to leftovers. In this study, the food waste fraction of canteen leftovers was identified as an optimal diet for black soldier fly (Hermetia illucens) larvae based on 50% higher consumption and 15% higher waste reduction indices compared with control chicken feed diet. Although the digestibility of food waste was nearly twice as high, the conversion efficiency of ingested and digested chicken feed remains unparalleled (17.9 ± 0.6 and 37.5 ± 0.9 in CFD and 7.9 ± 0.9 and 9.6 ± 1.0 in FWD, respectively). The oil separator waste fraction, however, inhibited biomass gain by at least 85% and ultimately led to a larval mortality of up to 96%. In addition to monitoring larval development, we characterized physicochemical properties of pre- and post-process food waste substrates. High-throughput amplicon sequencing identified Firmicutes, Proteobacteria, and Bacteroidota as the most abundant phyla, and Morganella, Acinetobacter, and certain Lactobacillales species were identified as indicator species. By using metagenome imputation, we additionally gained insights into the functional spectrum of gut microbial communities. We anticipate that the results will contribute to the development of decentralized waste-management sites that make use of larvae to process food waste as it has become common practice for biogas plants.

Identification of Bacteria in Two Food Waste Black Soldier Fly Larvae Rearing Residues

Significant economic, environmental, and social impacts are associated with the avoidable disposal of foods worldwide. Mass-rearing of black soldier fly (Hermetia illucens) larvae using organic wastes and food- and agro-industry side products is promising for recycling resources within the food system. One current challenge of this approach is ensuring a reliable and high conversion performance of larvae with inherently variable substrates. Research has been devoted to increasing rearing performance by optimizing substrate nutrient contents and ratios, while the potential of the substrate and larval gut microbiota to increase rearing performance remains untapped. Since previous research has focused on gut microbiota, here, we describe bacterial dynamics in the residue (i.e., the mixture of frass and substrate) of black soldier fly larvae reared on two food wastes (i.e., canteen and household waste). To identify members of the substrate and residue microbiota, potentially associated with rearing performance, bacterial dynamics were also studied in the canteen waste without larvae, and after inactivation by irradiation of the initial microbiota in canteen waste. The food waste substrates had similar microbiota; both were dominated by common lactic acid bacteria. Inactivation of the canteen waste microbiota, which was dominated by Leuconostoc, Bacillus, and Staphylococcus, decreased the levels of all rearing performance indicators by 31-46% relative to canteen waste with the native microbiota. In both food waste substrates, larval rearing decreased the bacterial richness and changed the physicochemical residue properties and composition over the rearing period of 12 days, and typical members of the larval intestinal microbiota (i.e., Providencia, Dysgonomonas, Morganella, and Proteus) became more abundant, suggesting their transfer into the residue through excretions. Future studies should isolate members of these taxa and elucidate their true potential to influence black soldier fly mass-rearing performance.