Transformation of pig manure by passage through the gut of black soldier fly larvae (Hermetia illucens): Metal speciation, potential pathogens and metal-related functional profiling

Synergistic impacts of antibiotics and heavy metals on Hermetia illucens: Unveiling dynamics in larval gut bacterial communities and microbial metabolites

Hermetia illucens larvae showcases remarkable bioremediation capabilities for both antibiotics and heavy metal contaminants. However, the distinctions in larval intestinal microbiota arising from the single and combined effects of antibiotics and heavy metals remain poorly elucidated. In this study, we delved into the details of larval intestinal bacterial communities and microbial metabolites when exposed to single and combined contaminants of oxytetracycline (OTC) and hexavalent chromium (Cr(VI)). After conversion, single contaminant-spiked substrate showed 75.5% of OTC degradation and 95.2% of Cr(VI) reductiuon, while combined contaminant-spiked substrate exhibited 71.3% of OTC degradation and 93.4% of Cr(VI) reductiuon. Single and combined effects led to differences in intestinal bacterial communities, mainly reflected in the genera of Enterococcus, Pseudogracilibacillus, Gracilibacillus, Wohlfahrtiimonas, Sporosarcina, Lysinibacillus, and Myroide. Moreover, these effects also induced differences across various categories of microbial metabolites, which categorized into amino acid and its metabolites, benzene and substituted derivatives, carbohydrates and its metabolites, heterocyclic compounds, hormones and hormone-related compounds, nucleotide and its metabolites, and organic acid and its derivatives. In particular, the differences induced OTC was greater than that of Cr(VI), and combined effects increased the complexity of microbial metabolism compared to that of single contaminant. Correlation analysis indicated that the bacterial genera, Preudogracilibacillus, Enterococcus, Sporosarcina, Lysinibacillus, Wohlfahrtiimonas, Ignatzschineria, and Fusobacterium exhibited significant correlation with significant differential metabolites, these might be used as indicators for the resistance and bioremediation of OTC and Cr(VI) contaminants. These findings are conducive to further understanding that the metabolism of intestinal microbiota determines the resistance of Hermetia illucens to antibiotics and heavy metals.

Stimulating the biofilm formation of Bacillus populations to mitigate soil antibiotic resistome during insect fertilizer application

Antibiotic resistance in soil introduced by organic fertilizer application pose a globally recognized threat to human health. Insect organic fertilizer may be a promising alternative due to its low antibiotic resistance. However, it is not yet clear how to regulate soil microbes to reduce antibiotic resistance in organic fertilizer agricultural application. In this study, we investigated soil microbes and antibiotic resistome under black soldier fly organic fertilizer (BOF) application in pot and field systems. Our study shows that BOF could stimulate ARB (antibiotic resistant - bacteria) - suppressive Bacillaceae in the soil microbiome and reduce antibiotic resistome. The carbohydrate transport and metabolism pathway of soil Bacillaceae was strengthened, which accelerated the synthesis and transport of polysaccharides to form biofilm to antagonistic soil ARB, and thus reduced the antibiotic resistance. We further tested the ARB - suppressive Bacillus spp. in a microcosm assay, which resulted in a significant decrease in the presence of ARGs and ARB together with higher abundance in key biofilm formation gene (epsA). This knowledge might help to the development of more efficient bio-fertilizers aimed at mitigating soil antibiotic resistance and enhancing soil health, in particular, under the requirements of global "One Health".

Black soldier fly larvae bioconversion and subsequent composting promote larval frass quality during pig and chicken manure transformation process

This research systematically assessed the changes in carbon, nitrogen and microbial profiling during pig and chicken manure transformation by black soldier fly larvae (BSFL) and subsequent composting process. BSFL had higher conversion efficiency for chicken manure. The pH, phosphorus and potassium contents in fresh BSFL frass increased than raw manure, but conductivity, total-/nitrate-/ammonium-nitrogen decreased. After BSFL conversion, pig manure had a larger nitrogen loss (25 %) while chicken manure had a larger carbon loss (32 %). During subsequent composting, the indicator changes (e.g. humus, ammonium nitrogen) in frass composts basically remained stable after 20-30 days. Compared to natural composts, frass composts had higher humification degree, cellulase activities, and more cellulose-degrading bacteria. Subsequent composting further reduced potential pathogens (reduced by 98.9 %-99.7 % than raw manure), and elevated the aromaticity and humification of frass. The findings gave an insight into the maturation management of manure-sourced insect frass.

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.

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.

Effect of moisture content on larval gut microbiome and the conversion of pig manure by black soldier fly

The study investigated the influence of varied moisture levels in pig manure on the gut microbiome of black soldier fly larvae (BSFL) and their waste conversion efficiency. This encompassed alterations in nutrient components of both BSFL and pig manure, diversity and characterization of the BSFL gut microbiota, and the reciprocal effects between the BSFL gut microbiota and their growth performance and nutrient composition. Additionally, the investigation delved into the changes in the bacterial community and the presence of potential pathogenic bacteria in pig manure. An initial mixture of fresh pig manure and wheat bran was prepared with a 60 % moisture content (Group A). Distilled water was subsequently added to adjust the moisture levels, resulting in mixtures with 65 % (Group B), 70 % (Group C), and 75 % (Group D) moisture content. Each group underwent BSFL digestion over ten days. Groups C (3.87 ± 0.05 mg/worm) and D (3.97 ± 0.08 mg/worm) showed significantly higher bioconversion efficiencies and enhanced BSFL growth compared to Groups A (2.66 ± 0.21 mg/worm) and B (3.09 ± 0.09 mg/worm) (P < 0.05). A 75 % moisture level was identified as ideal, positively influencing fecal conversion efficiency (FCE) (9.57 ± 0.14 %), crude fat intake (8.92 ± 0.56 %), protein (46.60 ± 0.54 %), and total phosphorus (1.37 ± 0.08 %) from pig manure, and subsequent nutrient accumulation in BSFLs. A decline in larval crude ash content indicated higher organic matter and an increased pig manure conversion rate with elevated moisture. High-throughput sequencing and diversity analyses confirmed different moisture contents influenced the BSFL gut microbiota. Bacteroidetes (32.7-62.0 %), Proteobacteria (6.8-29.3 %), Firmicutes (5.8-23.4 %), and Actinobacteria (1.9-29.0 %) were predominant phyla. A 75 % moisture content significantly impacted the BSFL biomass conversion and growth performance. Additionally, Larval feces met non-hazardous fertilizer standards, according to NY-525 (2012).

Reducing the mass and decreasing the bioavailability of heavy mental from organic wastes treated by black soldier fly larvae

Black soldier fly larvae (BSFL), Hermetia illucens L., are widely used to reduce the mass of various wastes. However, the potential metal tolerance mechanisms during periods of waste bioconversion by BSFL remain largely unknown. To further reveal the mechanisms, BSFL were used to treat the agricultural organic wastes, including pig manure (PM), cow manure (COM), spent mushroom substrate (SMS), and wet distiller grains (WDG). After these individual and combined waste(s) were treated by BSFL, we investigated the waste reduction rates and evaluated the responses of BSFL gut microbes to heavy metals of agricultural organic wastes. Additionally, the colloidal particles of residual wastes were characterized by combing energy dispersive X-ray (EDX) spectroscopy, Size potential, Zeta potential, and excitation-emission matrix (EEM) spectroscopy. Results indicated that the waste reduction rates were up to 74% in COM+WDG and 69% in WDG, most of heavy metals (e.g., Zn and Co) from organic wastes were not accumulated in the bodies of mature larvae after treatment. Further, results obtained from the prediction of gene function on the basis of 16 S rRNA data revealed that the presence of multi-resistance genes in the gut of BSFL can help the larvae resist Zn and/or Co stress. In addition, the drug sensitivity test implied that BSFL5_L and BSFL6_L from BSFL gut bacterial strains have multi-resistance to Co and Zn. Additionally, EDX results revealed that the colloidal particles in five waste residues after BSFL treatment are mainly consisted of Fe, Ca and Si, which can capture heavy metals (e.g., Cu, Mn). Results from EEM spectroscopy and PARAFAC showed that tryptophan-like and humic-like accumulatively account for 56%- 68% of all components. Importantly, these two components could strongly bind the metal elements and form colloidal particles with high stability, and therefore reduce the heavy metal pollution of agricultural organic wastes. Our findings offered an environment-friendly method to treat agricultural organic wastes, which would be far-reaching influence to our environment.

Insights into the reduction of antibiotic-resistant bacteria and mobile antibiotic resistance genes by black soldier fly larvae in chicken manure

The increasing prevalence of antibiotic-resistant bacteria (ARB) from animal manure has raised concerns about the potential threats to public health. The bioconversion of animal manure with insect larvae, such as the black soldier fly larvae (BSFL, Hermetia illucens [L.]), is a promising technology for quickly attenuating ARB while also recycling waste. In this study, we investigated BSFL conversion systems for chicken manure. Using metagenomic analysis, we tracked ARB and evaluated the resistome dissemination risk by investigating the co-occurrence of antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and bacterial taxa in a genetic context. Our results indicated that BSFL treatment effectively mitigated the relative abundance of ARB, ARGs, and MGEs by 34.9%, 53.3%, and 37.9%, respectively, within 28 days. Notably, the transferable ARGs decreased by 30.9%, indicating that BSFL treatment could mitigate the likelihood of ARG horizontal transfer and thus reduce the risk of ARB occurrence. In addition, the significantly positive correlation links between antimicrobial concentration and relative abundance of ARB reduced by 44.4%. Moreover, using variance partition analysis (VPA), we identified other bacteria as the most important factor influencing ARB, explaining 20.6% of the ARB patterns. Further analysis suggested that antagonism of other bacteria on ARB increased by 1.4 times, while nutrient competition on both total nitrogen and crude fat increased by 2.8 times. Overall, these findings provide insight into the mechanistic understanding of ARB reduction during BSFL treatment of chicken manure and provide a strategy for rapidly mitigating ARB in animal manure.

Upcycling of recycled minerals from sewage sludge through black soldier fly larvae (Hermetia illucens): Impact on growth and mineral accumulation

Phosphorous (P) resources are finite. Sewage sludge recyclates (SSR) are not only of interest as plant fertilizer but also as potential source of minerals in animal nutrition. However, besides P and calcium (Ca), SSR contain heavy metals. Under EU legislation, the use of SSR derivatives in animal feed is not permitted, but given the need to improve nutrient recycling, it could be an environmentally sound future mineral source. Black soldier fly larvae (BSFL) convert low-grade biomass into valuable proteins and lipids, and accumulate minerals in their body. It was hypothesized that BSFL modify and increase their mineral content in response to feeding on SSR containing substrates. The objective was to evaluate the upcycling of minerals from SSR into agri-food nutrient cycles through BSFL. Growth, nutrient and mineral composition were compared in BSFL reared either on a modified Gainesville fly diet (FD) or on FD supplemented with either 4% of biochar (FD + BCH) or 3.6% of single-superphosphate (FD + SSP) recyclate (n = 6 BSFL rearing units/group). Larval mass, mineral and nutrient concentrations and yields were determined, and the bioaccumulation factor (BAF) was calculated. The FD + SSP substrate decreased specific growth rate and crude fat of BSFL (P < 0.05) compared to FD. The FD + SSP larvae had higher Ca and P contents and yields but the BAF for Ca was lowest. The FD + BCH larvae increased Ca, iron, cadmium and lead contents compared to FD. Larvae produced on FD + SSP showed lower lead and higher arsenic concentration than on FD + BCH. Frass of FD + BCH had higher heavy metal concentration than FD + SSP and FD (P < 0.05). Except for cadmium and manganese, the larval heavy metal concentration was below the legally permitted upper concentrations for feed. In conclusion, the SSR used could enrich BSFL with Ca and P but at the expense of growth. Due to the accumulation of Cd and Mn, BSFL or products thereof can only be a component of farmed animal feed whereas in BSFL frass heavy metal concentrations remained below the upper limit authorized by EU.

Effects of straw addition on the physicochemical and microbial features of black soldier fly larvae frass derived from fish meat and bone meal

Black soldier fly larvae (BSFL) hold great promise for sustainable management of meat and bone meal (MBM), a kind of organic waste. Harvested BSFL frass can be used as soil amendment or organic fertilizer. This study evaluated the quality and microbial profile in the frass of BSFL, fed with fish MBM containing 0% (CK), 1% (T1), 2% (T2) and 3% (T3) of rice straw. Results suggested straw addition into fish MBM had no significant impacts on BSFL weight; however, straw addition remarkably affected waste reduction and conversion efficiency, as well as physicochemical properties including electric conductivity, organic matter (OM) and total phosphorus contents in frass. Fourier transform infrared analysis indicated that increasing levels of cellulose and lignin might not be fully degraded or transformed by BSFL when more straw was introduced into substrates. Straw addition had hardly significant influences on microbial richness or evenness in BSFL frass, only T3 treatment remarkably elevated the phylogenetic diversity value more than the control. Bacteroidetes, Proteobacteria, Actinobacteria and Firmicutes were the most dominant phyla. Genera Myroides, Acinetobacter and Paenochrobactrum maintained high abundances in all frass samples. Elements including OM, pH and Na were key factors in shaping the microbiological characteristics of BSFL frass. Our findings helped to understand the effects of fish MBM waste manipulation on BSFL frass qualities and contributed to the further application of BSFL frass.

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.

Analysis of heavy metals in the conversion of lake sediment and restaurant waste by black soldier fly (Hermetia illucens)

The risk posed by heavy metals makes it difficult to dispose of sediment contaminants from dredging lakes in China. Black soldier fly (Hermetia illucens) can convert organic waste, such as restaurant waste and lake sediment, to high-value-added protein feed and fertilizer. Experimental groups were formed in this study to explore the conversion of heavy metals present in the mixture of restaurant waste and lake sediment by black soldier fly larvae (BSFL). The results demonstrated that BSFL could survive in pure sediment with an 84.76% survival rate. Relative to the substrate, BSFL could accumulate 70-90% zinc (Zn), chromium (Cr), copper (Cu), and 20-40% cadmium (Cd) and lead (Pb). The experimental group 2:3, with 40% lake sediment and 60% restaurant waste, was the best group after conversion for 15 days, which showed a 95.24% survival rate of BFSL, 82.20 mg average weight of BFSL, 8.92 mm average length of BFSL, with varying content of heavy metals such as Cu (43.22 mg/kg), Zn (193.31 mg/kg), Cd (1.58 mg/kg), Cr (25.30 mg/kg) Cr, and Pb (38.59 mg/kg) in BSFL. Furthermore, the conversion residue conforms to the relevant standards of organic fertilizer in China and can be used as organic fertilizer. Overall, the present study shows that black soldier flies can improve the resource utilization of lake sediment, especially by reducing the effect of heavy metals.

Inoculation with black soldier fly larvae alters the microbiome and volatile organic compound profile of decomposing food waste

The black soldier fly (BSF; Hermetia illucens) is used in sustainable processing of many types of organic waste. However, organic waste being decomposed by BSF produces strong odors, hindering more widespread application. The odor components and how they are produced have yet to be characterized. We found that digestion of food waste by BSF significantly alters the microbial flora, based on metagenomic analyses, and the odor components generated, as shown by thermal desorption gas chromatography mass spectrometry analysis. Inoculation with BSF significantly decreased production of volatile organic sulfur compounds (dimethyl disulfide and dimethyl trisulfide), which are known to be released during methionine and cysteine metabolism by Lactobacillus and Enterococcus bacteria. BSF inoculation significantly changed the abundance of Lactobacillus and Enterococcus and decreased microbial diversity overall. These findings may help in optimizing use of BSF for deodorization of composting food waste.

Effects of Disinfectants on Larval Growth and Gut Microbial Communities of Black Soldier Fly Larvae

The use of the black soldier fly has been demonstrated to be effective in the treatment of swine manure. Since the outbreaks of ASFV, prevention procedures, including manure disinfection, have changed dramatically. Glutaraldehyde (GA) and potassium peroxymonosulfate (PPMS) have been shown to be effective in the prevention of this pathogen and are thus widely used in the disinfection of swine manures, etc. However, research on the effects of disinfectants in manures on the growth of BSFL and gut microbiota is scarce. The goal of this study was to determine the effects of GA and PPMS on BSFL growth, manure reduction, and gut microbiota. In triplicate, 100 larvae were inoculated in 100 g of each type of manure compound (manure containing 1% GA treatment (GT1), manure containing 0.5% GA treatment (GT2), manure containing 1% PPMS treatment (PT1), manure containing 0.5% PPMS treatment (PT2), and manure without disinfectant (control)). After calculating the larval weight and waste reduction, the larval gut was extracted and used to determine the microbial composition. According to the results, the dry weights of the larvae fed PT1-2 (PT1: 86.7 ± 4.2 mg and PT2: 85.3 ± 1.3 mg) were significantly higher than those of the larvae fed GT1-2 (GT1: 72.5 ± 2.1 mg and GT2: 70 ± 2.8 mg) and the control (64.2 ± 5.8 mg). There was a 2.8-4.03% higher waste reduction in PT1-2 than in the control, and the waste reduction in GT1-2 was 7.17-7.87% lower than that in the control. In a gut microbiota analysis, two new genera (Fluviicola and Fusobacterium) were discovered in PT1-2 when compared to GT1-2 and the control. Furthermore, the disinfectants did not reduce the diversity of the microbial community; rather, Shannon indices revealed that the diversities of GT1-2 (GT1: 1.924 ± 0.015; GT2: 1.944 ± 0.016) and PT1 (1.861 ± 0.016) were higher than those of the control (1.738 ± 0.015). Finally, it was found that both disinfectants in swine manures at concentrations of 1% and 0.5% may be beneficial to the complexity and cooperation of BSFL gut microbiota, according to an analysis of microbial interactions.

Assessing Nursery-Finishing Pig Manures on Growth of Black Soldier Fly Larvae

Livestock manure is an important component of agricultural organic waste, and in recent years, with the development of research on the bioconversion of manure, BSFs have been proven to be useful in the treatment of a variety of livestock wastes. In-depth research on the composition of manure and its effect on the development of BSFL is, however, very scarce. The purpose of this study was to identify the parameters that influenced the growth of BSFL that was fed fattening pig manure. The pH, moisture, and nutrients of the fattening manures (namely, nursery, growing, and finishing pig manures) were measured. To examine the influence of manure types on larval growth, 100 larvae were inoculated in 100 g of each type of manure in triplicate. According to the findings, larvae fed finishing pig manure had the lowest dry weight (30.2 ± 6.1 mg) compared to those fed growing (58.2 ± 7.3 mg) or nursery (65.5 ± 6.2 mg) pig manure. The correlation coefficients (r) between the nutrients in the manure and the weight of the larvae were calculated. Hemicellulose had the greatest |r| value (0.9569). Further research revealed that larvae raised on hemicellulase-pretreated finishing pig manure frequently weighed 21-30% (days 2-8) more than larvae raised on control manure. In conclusion, hemicellulose was a significant component that might hinder larval growth. The results of this study could be used to improve the system before it is put into use.

Migration and Transformation of Cd in Pig Manure-Insect Frass (Hermetia illucens)-Soil-Maize System

Little is known about the fate of heavy metals in the recycling system of animal manure-black soldier fly larvae (BSFL) transformation-larval frass application. In this work, BSFL-transformed pig manure with different concentrations of exogenous cadmium (Cd) (0, 3, 15, 30 mg kg^-1), and the obtained BSFL frass fertilizer were further used in pot experiments of maize planting to explore Cd migration during the whole recycling system. Results showed that Cd addition to pig manure had no significant effects on BSFL growth or BSFL transformation performance. The Cd concentrations in BSFL frass were 10.9-19.8% lower than those in pig manure, while those in BSFL bodies were 2.3-4.0-times those of pig manure. For maize planting, only 30 mg kg^-1 of Cd treatment significantly inhibited maize growth. The BSFL frass application (under exogenous Cd treatment) enhanced Cd contents in the aboveground and underground parts of maize (3.3-57.6-times) and those in soil (0.5-1.7-times) compared with CK (no Cd addition). Additionally, 61.2-73.5% of pig manure-sourced Cd was transformed into BSFL frass and the rest entered BSFL bodies. Only a small part (0.31-1.34%) of manure-sourced Cd entered maize plants. BSFL transformation decreased the proportions of weak acid-dissolved Cd from 44.2-53.0% (manure) to 37.3-46.0% (frass). After frass application, the proportions of weak acid-dissolved Cd in soil were further decreased to 17.8-42.5%, while the residual fractions of Cd increased to 27.2-67.7%. The findings provided a theoretical basis for the rational application of BSFL frass fertilizers sourced from heavy-metal-contaminated manure.

Influence of different inoculation densities of black soldier fly larvae (Hermetia illucens) on heavy metal immobilization in swine manure

The disposal of organic waste by the biocomposting of black soldier fly larvae (BSFL) has drawn broad attention. However, the discrepancies in heavy metal immobilization between BSFL biocomposting with different inoculation densities and aerobic composting need to be further researched. In this study, BSFL with inoculation densities of 0.08%, 0.24% and 0.40% was added to swine manure to investigate its influence on heavy metal bioaccumulation and bioavailability. The physicochemical properties, BSFL growth performance and amino acid contents were measured. The results showed that the germination index, total prepupal yield and bioavailable fraction removal rate (%) of Cr and Pb at an inoculation density of 0.40% of BSFL were the highest among all of the BSFL biocomposting groups. Although the bioaccumulation factor and heavy metal (Cd, Cr, Cu and Zn) concentrations of the BSFL body from swine manure with inoculation densities of 0.24% and 0.40% of BSFL were similar, the BSFL inoculation density of 0.40% had the best absorption effect on these heavy metals in terms of total prepupal yield. Therefore, this study provides a basis for exploring the optimal inoculation density of BSFL biocomposting to reduce the harmful effects of heavy metals in swine manure.

Effects of three major nutrient contents, compost thickness and treatment time on larval weight, process performance and residue component in black soldier fly larvae (Hermetia illucens) composting

The cellulose content in vegetable waste (VW) is high and cannot be directly digested by black soldier fly larvae (BSFL). In this study, in order to treat VW using BSFL composting, kitchen waste (KW) is used as the only nutritional supplement for VW to analyze the effects of the different contents of crude protein (CP), crude fat (EE), carbohydrate (3C), compost thickness (CT), and treatment time on the larval weight (LW), survival rate (SR), dry matter reduction rate (DMR), bioconversion rate (BCR), physical and chemical properties of BSFL sand and changes in the microbial community. Our results showed that when the average 3C content increased by 40%, the average LW increased by 47.6%, and the SR, DMR, BCR, and organic matter (OM) content increased by 16.82%, 8.5%, 4.77%, and 3.86%, respectively. In contrast, when the average compost thickness increased by 5 cm, the average weight of BSFL decreased by 22.64%, while the SR of larvae, DMR, BCR, OM, and total nutrients (TN + P₂O₅ + K₂O) decreased by 5%, 5.2%, 4.42%, 9.6%, and 0.78%, respectively. Germination test showed that BSFL sand alone could not be used as soilless culture substrate. After BSFL treatment, we found that the dominant phyla in BSFL sand were Firmicutes (95.77%), Proteobacteria (2.54%), Actinobacteria (0.74%), and Chloroflexi (0.6%). Our results indicate that BSFL composting is an effective method of treating VW, and 3C content and CT have a significant effect on BSFL composting.

Bioconversion of chicken meat and bone meal by black soldier fly larvae: Effects of straw addition on the quality and microbial profile of larval frass

Meat and bone meal (MBM) is a kind of animal waste with high nutritive values. Bioconversion of MBM by black soldier fly larvae (BSFL) has great potential to obtain high-quality organic fertilizers. However, limited information is available on MBM waste manipulation to enhance BSFL frass quality. In the present study, BSFL were fed with chicken MBM containing increasing levels of rice straw (CK (0%), T1 (1%), T2 (1%), and T3 (3%)). The effects of straw addition into MBM on the quality and microbial profile of BSFL frass were evaluated. Results showed that MBM amended with straw did not significantly affect the body weight of BSFL and most of the nutrients (e.g. pH, EC, TN, TP and Na) in larval frass. Compared to other treatments, T1 sample had the highest organic matter (OM) value, implying proper straw addition could increase OM contents in frass. Fourier transform infrared (FTIR) analysis showed that straw addition might enhance the decomposition of aliphatic carbons and polysaccharides during MBM digestion process. Moreover, T1 sample had the highest microbial richness and Shannon diversity indices. It was supposed that proper straw addition in MBM helped build a more balanced diet and contributed to the BSFL gut health, consequently stimulating the gut microbe-mediated substances transformation or decomposition and promoting the microbial diversity in frass. Compared to CK, straw addition had significant influence on the abundances of Firmicutes, Bacteroidetes and Fusobacteria in frass. Elements including OM, TK and Na played important roles in shaping the microbial profile of BSFL frass.

In Vitro Evaluation of Antimicrobial Peptides from the Black Soldier Fly (Hermetia Illucens) against a Selection of Human Pathogens

Antimicrobial peptides (AMPs) are being explored as alternatives to traditional antibiotics to combat the rising antimicrobial resistance. Insects have proven to be a valuable source of new, potent AMPs with large structural diversity. For example, the black soldier fly has one of the largest AMP repertoires ever recorded in insects. Currently, however, this AMP collection has not yet undergone antimicrobial evaluation or in-depth in vitro characterization. This study evaluated the activity of a library of 36 black soldier fly AMPs against a panel of human pathogens (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Aspergillus fumigatus) and a human cell line (MRC5-SV2). The activity profile of two cecropins (Hill-Cec1 and Hill-Cec10) with potent Gram-negative activity, was further explored by characterizing their hemolysis, time-to-kill kinetics, membrane-permeabilization properties, and anti-biofilm activity. Hill-Cec1 and Hill-Cec10 also showed high activity against other bacterial species, including Klebsiella pneumoniae and multi-drug resistant P. aeruginosa. Both AMPs are bactericidal and have a rapid onset of action with membrane-permeabilizing effects. Hill-Cec1 and Hill-Cec10 were also able to prevent P. aeruginosa biofilm formation, but no relevant effect was seen on biofilm eradication. Overall, Hill-Cec1 and Hill-Cec10 are promising leads for new antimicrobial development to treat critical infections caused by Gram-negative pathogens such as P. aeruginosa.

IMPORTANCE With the ever growing antimicrobial resistance, finding new candidates for antimicrobial drug development is indispensable. Antimicrobial peptides have steadily gained attention as alternatives for conventional antibiotics, due to some highly desirable characteristics, such as their low propensity for resistance development. With this article, we aim to upgrade the knowledge on the activity of black soldier fly antimicrobial peptides and their potential as future therapeutics. To achieve this, we have evaluated for the first time a library of 36 synthetically produced peptides from the black soldier fly against a range of human pathogens and a human cell line. Two selected peptides have undergone additional testing to characterize their antimicrobial profile against P. aeruginosa, a clinically important Gram-negative pathogen with a high established resistance. Overall, this research has contributed to the search for new peptide drug leads to combat the rising antimicrobial resistance.

Effects of further composting black soldier fly larvae manure on toxic metals and resistant bacteria communities by cornstalk amendment

Rapid composting by black soldier fly larvae (BSFL) may be insufficient to maturation and humification of composting and further composting is necessary. The purpose of this study was to explore cornstalk addition on toxic metals (Cu, Zn, Pb and Cd), toxic metals resistance bacterial (TMRB) destiny and their relationship with physicochemical factors during BSFL manure composting. High-throughput sequencing was performed by six treatments, namely T1 to T6, where T1 to T3 were BSFL manures from chicken, pig and dairy manure, respectively, and T4 to T6 were same manures and utilized cornstalk to adjust C/N to 25. The results showed that cornstalk amendment could enhance the toxic metals immobilization rate compared to control treatments in the ultimate product. TMRB indicated that the major potential hosts bacteria were Firmicutes, Bacteroidota, Proteobacteria, Acidobacteriota and Actinobacteriota, and the sum relative abundance were 63.33%, 90.62%, 83.62%, 69.38%, 50.66% and 90.52% in T1 to T6 at the end of composting. Bacteria diversity and heat map revealed composting micro-ecology with additive cornstalk to remarkably effect main resistant bacterial distribution via adjusting environmental factors and potential hosts bacterial. Finally, T5 treatment was able to greatly decrease the TMRB abundance, and improve the ability of composting and ultimate product quality.

Microbial influence on reproduction, conversion, and growth of mass produced insects

One important feature of insect rearing is its apparent, and sometimes non-apparent, reliance on the bacterial ecosystem. Indeed, microbes contribute to insect nutrition, protection against natural enemies, and detoxification of dietary compounds, antibiotics, and insecticides. Further, microbes have been implicated as the source of signals and cues important to insect communication. But the incidence and general significance of these functions is only just being explored in the context of mass production of insects. Knowledge of the diversity and functional distribution of these microorganisms in mass-rearing systems is key to understanding microbial dynamics and to enhance system performance. Therefore, this brief review is a synthesis of literature surrounding insect rearing systems for the primary insects reared as food and feed (i.e. black soldier fly, Hermetia illucens (Diptera: Stratiomyidae), mealworms (Coleoptera: Tenebrionidae), and cricket (Orthoptera: Grylloidea) with a focus on recent advances pertaining to microbial contribution to reproduction, growth, and waste conversion.

Nature-Based Units as Building Blocks for Resource Recovery Systems in Cities

Cities are producers of high quantities of secondary liquid and solid streams that are still poorly utilized within urban systems. In order to tackle this issue, there has been an ever-growing push for more efficient resource management and waste prevention in urban areas, following the concept of a circular economy. This review paper provides a characterization of urban solid and liquid resource flows (including water, nutrients, metals, potential energy, and organics), which pass through selected nature-based solutions (NBS) and supporting units (SU), expanding on that characterization through the study of existing cases. In particular, this paper presents the currently implemented NBS units for resource recovery, the applicable solid and liquid urban waste streams and the SU dedicated to increasing the quality and minimizing hazards of specific streams at the source level (e.g., concentrated fertilizers, disinfected recovered products). The recovery efficiency of systems, where NBS and SU are combined, operated at a micro- or meso-scale and applied at technology readiness levels higher than 5, is reviewed. The importance of collection and transport infrastructure, treatment and recovery technology, and (urban) agricultural or urban green reuse on the quantity and quality of input and output materials are discussed, also regarding the current main circularity and application challenges.

Research trend analysis of composting based on Web of Science database

Bibliometric analysis was used in this study for the quantitative evaluation of current research trends on composting. The research articles indexed from the Science Citation Index-Expanded in Web of Science database published from 2000 to 2019 were investigated. The USA, China and Spain were the top three countries considering the number of papers. Amongst the research institutes, CSIC of Spain, Chinese Academy of Sciences and Agriculture & Agri-Food Canada ranked the top three in total publication amount. Journals that published a significant number of literature regarding topics of composting included Environmental Sciences & Ecology, Agriculture and Engineering. In terms of research content, keywords such as heavy metal, heavy metal and biodegradation appeared frequently. In addition, the analysis of keywords revealed the following research hotspots in future studies: investigation of heavy metal passivator, optimisation of composting conditioner, development of all kinds of microorganisms, rational management of the composting process and improvement of solid waste life cycle assessment. To some extent, it helps to understand the current global status and trends of the related research.

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.

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.