Systematic characterization and proposed pathway of tetracycline degradation in solid waste treatment by Hermetia illucens with intestinal microbiota

Hormesis of black soldier fly larva: Influence and interactions in livestock manure recycling

Black soldier fly larvae (BSFL) are considered important organisms, utilized as tools to transform waste including manure into valuable products. The growth and cultivation of BSFL are influenced by various factors, such as the presence of toxic substances in the feed and parasites. These factors play a crucial role in hormesis, and contributing to regulate these contaminants hermetic doses to get sustainable byproducts. This review aims to understand the effects on BSFL growth and activities in the presence of compounds like organic and inorganic pollutants. It also assesses the impact of microbes on BSFL growth and explores the bioaccumulation of pharmaceutical compounds, specifically focusing on heavy metals, pesticides, pharmaceuticals, indigenous bacteria, insects, and nematodes. The review concludes by addressing knowledge gaps, proposing future biorefineries, and offering recommendations for further research.

Biodegradation and bioaugmentation of tetracycline by Providencia stuartii TX2: Performance, degradation pathway, genetic background, key enzymes, and application risk assessment

The antibiotic tetracycline (TC) is an emerging pollutant frequently detected in various environments. Biodegradation is a crucial approach for eliminating TC contamination. However, only a few efficient TC-degrading bacteria have been isolated, and the molecular mechanisms of TC degradation, as well as their application potential, remain poorly understood. This study isolated a novel TC-degrading bacterium, Providencia stuartii TX2, from the intestine of black soldier fly larvae. TX2 exhibited remarkable performance, degrading 72.17 % of 400 mg/L TC within 48 h. Genomic analysis of TX2 unveiled the presence of antibiotic resistance genes and TC degradation enzymes. Transcriptomic analysis highlighted the roles of proteins related to efflux pumps, enzymatic transformation, adversity resistance, and unknown functions. Three TC degradation pathways were proposed, with TC being transformed into 27 metabolites through epimerization, hydroxylation, oxygenation, ring opening, and de-grouping, reducing TC toxicity. Additionally, TX2 significantly enhanced TC biodegradation in four TC-contaminated environmental samples and reduced antibiotic resistance genes and mobile genetic elements in chicken manure. This research provides insights into the survival and biodegradation mechanisms of Providencia stuartii TX2 and evaluates its potential for environmental bioremediation.

Screening of oxytetracycline-degrading strains in the intestine of the black soldier fly larvae and their degradation characteristics

The presence of excessive antibiotic residues poses a significant threat to human health and the environment. This study was designed to identify an effective oxytetracycline (OTC)-degrading strain through the screening of the intestine of black soldier fly larvae (BSFL). A strain designated "B2" was selected using a series of traditional microbial screening methods. It could be identified as Enterococcus faecalis by Gram staining and 16S rDNA sequencing, with a similarity of 99.93%. Its ability to degrade OTC was then assessed using high-performance liquid chromatography (HPLC). The degradation of the strain was characterized using a one-way test to assess the effects of the substrate concentration, inoculum amount, and initial pH on the degrading bacteria. The results indicate that strain B2 exhibited optimal OTC-degrading performance at a substrate concentration of 50 mg/L, with an inoculum amount of 6% and a pH value of 5.0. Specifically, strain B2 achieved degradation rates of 71.11%, 56.14%, and 45.03%. These findings demonstrate the effectiveness of strain B2 in degrading OTC, indicating its potential for use in environmental remediation efforts.

Microorganism Contribution to Mass-Reared Edible Insects: Opportunities and Challenges

The interest in edible insects' mass rearing has grown considerably in recent years, thereby highlighting the challenges of domesticating new animal species. Insects are being considered for use in the management of organic by-products from the agro-industry, synthetic by-products from the plastics industry including particular detoxification processes. The processes depend on the insect's digestive system which is based on two components: an enzymatic intrinsic cargo to the insect species and another extrinsic cargo provided by the microbial community colonizing-associated with the insect host. Advances have been made in the identification of the origin of the digestive functions observed in the midgut. It is now evident that the community of microorganisms can adapt, improve, and extend the insect's ability to digest and detoxify its food. Nevertheless, edible insect species such as Hermetia illucens and Tenebrio molitor are surprisingly autonomous, and no obligatory symbiosis with a microorganism has yet been uncovered for digestion. Conversely, the intestinal microbiota of a given species can take on different forms, which are largely influenced by the host's environment and diet. This flexibility offers the potential for the development of novel associations between insects and microorganisms, which could result in the creation of synergies that would optimize or expand value chains for agro-industrial by-products, as well as for contaminants.

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-based bioconversion of biosolids: Microbial community dynamics and fate of antibiotic resistance genes

Biosolids as by-products of wastewater treatment can contain a large spectrum of pathogens and antibiotic resistance genes (ARGs). Insect-based bioconversion using black soldier fly larvae (BSFL) is an emerging technology that has shown to reduce significant amounts of biosolids quickly and produce larvae biomass containing low heavy metal concentrations. However, to the best of our knowledge, this is the first study investigating the transfer of pathogens and ARGs from biosolids into the process' end-products, BSFL and frass. We hypothesized that BSF-based bioconversion can decrease the abundance of pathogenic bacteria and ARGs in biosolids. In this study, we performed BSFL feeding trials with biosolids blended or not blended with wheat bran, and wheat bran alone as a low bioburden diet (control). We conducted 16S rRNA amplicon sequencing to monitor changes of the BSFL-associated microbial community and the fate of biosolids-associated pathogens. A diverse set of ARGs (ermB, intl1, sul1, tetA, tetQ, tetW, and blaCTX-M-32) were quantified by qPCR and were linked to changes in substrate- and BSFL-associated microbiomes. BSF-based bioconversion of biosolids-containing substrates led to a significant reduction of the microbial diversity, the abundance of several pathogenic bacteria and the investigated ARGs (< 99 %). Feeding with a high bioburden biosolid diet resulted in a higher microbial diversity, and the accumulation of pathogenic bacteria and ARGs in the BSFL. Results of this study demonstrated that BSF-based bioconversion can be a suitable waste management technology to (1) reduce significant amounts of biosolids and (2) reduce the presence of pathogens and ARGs. However, the resulting larvae biomass would need to undergo further post-treatment to reduce the pathogenic load to allow them as animal feed.

Framework for evaluation of food safety in the circular food system

In order to minimise food waste, side streams from feed and food production are increasingly being (re-) used in food supply chains. Such reuse contributes to the desire to implement circularity in food and agricultural systems. However, the reuse of side products in circular food systems may impact food safety, for instance, contaminant residues present at low levels in biomass may accumulate when reusing streams. In order to assess potential food safety issues related to circular food systems, a framework has been developed in this study. Based on this framework, appropriate actions can be taken to prevent from human health risks. The framework consists of three steps: 1. Describing the changes in the food supply chain as a result of the circularity transition; 2. Identifying potential food safety hazards related to the change; and 3. Prioritising food safety hazards related to the circularity transition. For the prioritisation, both the presence of the hazards in final foods and the effects of the hazards on human health need to be assessed. Persistence of the hazard in the environment and potential transfer from the environment to the final food product are relevant elements to include. The framework was tested in three case studies, showing that it allows for a prioritisation between hazards. Based on the case study results, circularity not so much influences the health effects of the hazards, but rather their presence depending on the persistence and transfer of food safety hazards in a circular system.

Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

Identification of functional microflora underlying the biodegradation of sulfadiazine-contaminated substrates by Hermetia illucens

The increasing discharge of antibiotic residues into the natural environment, stemming from both human activities and animal farming, has detrimental effects on natural ecosystems and serves as a significant driving force for the spread of antibiotic resistance. Biodegradation is an important method for the elimination of antibiotics from contaminated substrates, but the identifying in situ microbial populations involved in antibiotic degradation is challenging. Here, DNA stable isotope probing (DNA-SIP) was employed to identify active sulfadiazine (SDZ) degrading microbes in the gut of black soldier fly larvae (BSFLs). At an initial SDZ concentration of 100 mg kg-1, the highest degradation efficiency reached 73.99% after 6 days at 28 °C. DNA-SIP revealed the incorporation of 13C6 from labeled SDZ in 9 genera, namely, Clostridum sensu stricto 1, Nesterenkonia, Bacillus, Halomonas, Dysgonomonas, Caldalkalibacillus, Enterococcus, g_unclassified_f_Xanthomonadaceae and g_unclassified_f_Micrococcaceae. Co-occurrence network analysis revealed that a significant positive correlation existed among SDZ degrading microbes in the gut microbiota, e.g., between Clostridium sensu stricto 1 and Nesterenkonia. Significant increases in carbohydrate metabolism, membrane transport and translation were crucial in the biodegradation of SDZ in the BSFL gut. These results elucidate the structure of SDZ-degrading microbial communities in the BSFL gut and in situ degradation mechanisms.

Characteristics of gut bacterial microbiota of black soldier fly (Diptera: Stratiomyidae) larvae effected by typical antibiotics

As agents in an emerging technology, Hermetia illucens (Linnaeus, 1758) (Diptera: Stratiomyidae) larvae, black soldier fly, have shown exciting potential for degrading antibiotics in organic solid waste, a process for which gut microorganisms play an important role. This study investigated the characteristics of larval gut bacterial communities effected by typical antibiotics. Initially, antibiotics significantly reduced the diversity of gut bacterial species. After 8 days, diversity recovered to similar to that of the control group in the chlortetracycline, tylosin, and sulfamethoxazole groups. Proteobacteria, Firmicutes, and Actinobacteriota were the dominant phyla at the initial BSFL gut. However, after 4 days treatment, the proportion of Actinobacteriota significantly decreased, but Bacteroidota notably increased. During the conversion process, 18, 18, 17, 21, and 19 core genera were present in the chlortetracycline, sulfamethoxazole, tylosin, norfloxacin, and gentamicin groups, respectively. Pseudomonas, Actinomyces, Morganella, Providencia and Klebsiella might be the important genera with extraordinary resistance and degradation to antibiotics. Statistical analyses of COGs showed that antibiotics changed the microbial community functions of BSFL gut. Compared with the control group, (i) the chlortetracycline, sulfamethoxazole, and tylosin groups showed significant increase in the classification functions of transcription, RNA processing and modification，and so on, (ii) the norfloxacin and gentamicin groups showed significant increase in defense mechanisms and other functions. Note that we categorized the response mechanisms of these classification functions to antibiotics into resistance and degradation. This provides a new perspective to deeply understand the joint biodegradation behavior of antibiotics in environments, and serves as an important reference for further development and utilization of microorganisms-assisted larvae for efficient degradation of antibiotics.

Cellulose-degrading bacteria improve conversion efficiency in the co-digestion of dairy and chicken manure by black soldier fly larvae

Black soldier fly larvae (BSFL) have potential utility in converting livestock manure into larval biomass as a protein source for livestock feed. However, BSFL have limited ability to convert dairy manure (DM) rich in lignocellulose. Our previous research demonstrated that feeding BSFL with mixtures of 40% dairy manure and 60% chicken manure (DM40) provides a novel strategy for significantly improving their efficiency in converting DM. However, the mechanisms underlying the efficient conversion of DM40 by BSFL are unclear. In this study, we conducted a holistic study on the taxonomic stucture and potential functions of microbiota in the larval gut and manure during the DM and DM40 conversion by BSFL, as well as the effects of BSFL on cellulosic biodegradation and biomass production. Results showed that BSFL can consume cellulose and other nutrients more effectively and harvest more biomass in a shorter conversion cycle in the DM40 system. The larval gut in the DM40 system yielded a higher microbiota complexity. Bacillus and Amphibacillus in the BSFL gut were strongly correlated with the larval cellulose degradation capacity. Furthermore, in vitro screening results for culturable cellulolytic microbes from the larval guts showed that the DM40 system isolated more cellulolytic microbes. A key bacterial strain (DM40L-LB110; Bacillus subtilis) with high cellulase activity from the larval gut of DM40 was validated for potential industrial applications. Therefore, mixing an appropriate proportion of chicken manure into DM increased the abundance of intestinal bacteria (Bacillus and Amphibacillus) producing cellulase and improved the digestion ability (particularly cellulose degradation) of BSFL to cellulose-rich manure through changes in microbial communities composition in intestine. This study reveals the microecological mechanisms underlying the high-efficiency conversion of cellulose-rich manure by BSFL and provide potential applications for the large-scale cellulose-rich wastes conversion by intestinal microbes combined with BSFL.

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.

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.

Establishment of highly efficient transgenic system for black soldier fly (Hermetia illucens)

The black soldier fly (BSF), Hermetia illucens, is a promising insect for mitigating solid waste problems as its larvae are able to bioconvert organic waste into valuable biomass. We recently reported a high-quality genome assembly of the BSF; analysis of this genome sequence will further the understanding of insect biology and identify genes that can be manipulated to improve efficiency of bioconversion. To enable genetic manipulation of the BSF, we have established the first transgenic methods for this economically important insect. We cloned and identified the ubiquitous actin5C promoter (Hiactin5C-p3k) and 3 endogenous U6 promoters (HiU6:1, HiU6:2, and HiU6:3). The Hiactin5C promoter was used to drive expression of a hyperactive variant of the piggyBac transposase, which exhibited up to 6-fold improvement in transformation rate when compared to the wild-type transposase. Furthermore, we evaluated the 3 HiU6 promoters using this transgenic system. HiU6:1 and HiU6:2 promoters provided the highest knockdown efficiency with RNAi and are thus promising candidates for future Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) development. Overall, our findings provide valuable genetic engineering toolkits for basic research and genetic manipulation of the BSF.

Improvement in bioconversion efficiency and reduction of ammonia emission by introduction of fruit fermentation broth in a black soldier fly larvae and kitchen waste conversion system

The black soldier fly (BSF), Hermetia illucens (Diptera: Stratiomyidae), is an insect commonly used for the bioconversion of various organic wastes. Not only can the BSF convert organic waste into macromolecular organic substances, such as insect proteins, but it can also lessen the pollution associated with these waste products by reducing ammonia emissions, for example. In this study, we measured the effects of adding fruit fermentation broth (Fer) and commercial lactic acid bacteria fermentation broth (Em) to kitchen waste (KW), as deodorizing auxiliary substances, on the growth performance of black soldier fly larvae (BSFL), the intestinal flora structure of BSFL, the ammonia emission from the KW substrate, and the microbial community structure of the KW substrate. We found that the addition of Fer or Em increased the body weight of BSFL after 6 d of culture, increasing the growth rate by 9.96% and 7.96%, respectively. The addition of Fer not only reduced the pH of the KW substrate but also increased the relative abundance of probiotics, such as Lactobacillus, Lysinibacillus, and Vagococcus, which inhibited the growth of ammonifiers such as Bacillus, Oligella, Paenalcaligenes, Paenibacillus, Pseudogracilibacillus, and Pseudomonas, resulting in the reduction of ammonia emission in the KW substrate. Moreover, the addition of Fer or Em significantly increased the relative abundances of Bacteroides, Campylobacter, Dysgonomonas, Enterococcus, and Ignatzschineria in the gut of BSFL and increased the species diversity and richness in the KW substrate. Our findings provide a novel way to improve the conversion rate of organic waste and reduce the environmental pollution caused by BSF.

Comparative Metagenomic and Metatranscriptomic Analyses Reveal the Response of Black Soldier Fly (Hermetia illucens) Larvae Intestinal Microbes and Reduction Mechanisms to High Concentrations of Tetracycline

Black soldier fly (Hermetia illucens L) larvae (BSFL) possess remarkable antibiotic degradation abilities due to their robust intestinal microbiota. However, the response mechanism of BSFL intestinal microbes to the high concentration of antibiotic stress remains unclear. In this study, we investigated the shift in BSFL gut microbiome and the functional genes that respond to 1250 mg/kg of tetracycline via metagenomic and metatranscriptomic analysis, respectively. The bio-physiological phenotypes showed that the survival rate of BSFL was not affected by tetracycline, while the biomass and substrate consumption of BSFL was slightly reduced. Natural BSFL achieved a 20% higher tetracycline degradation rate than the germ-free BSFL after 8 days of rearing. Metagenomic and metatranscriptomic sequencing results revealed the differences between the entire and active microbiome. Metatranscriptomic analysis indicated that Enterococcus, Vagococcus, Providencia, and Paenalcaligenes were the active genera that responded to tetracycline. Furthermore, based on the active functional genes that responded to tetracycline pressure, the response mechanisms of BSFL intestinal microbes were speculated as follows: the Tet family that mediates the expression of efflux pumps expel tetracycline out of the microbes, while tetM and tetW release it from the ribosome. Eventually, tetracycline was degraded by deacetylases and novel enzymes. Overall, this study provides novel insights about the active intestinal microbes and their functional genes in insects responding to the high concentration of antibiotics.

Mitigation of antibiotic resistome in swine manure by black soldier fly larval conversion combined with composting

The increasing prevalence of antibiotic resistance genes (ARGs) in animal manure has attracted considerable attention because of their potential contribution to the development of multidrug resistance worldwide. Insect technology may be a promising alternative for the rapid attenuation of ARGs in manure; however, the underlying mechanism remains unclear. This study aimed to evaluate the effects of black soldier fly (BSF, Hermetia illucens [L.]) larvae conversion combined with composting on ARGs dynamics in swine manure and to uncover the mechanisms through metagenomic analysis. Compared to natural composting (i.e. without BSF), BSFL conversion combined with composting reduced the absolute abundance of ARGs by 93.2 % within 28 days. The rapid degradation of antibiotics and nutrient reformulation during BSFL conversion combined with composting indirectly altered manure bacterial communities, resulting in a lower abundance and richness of ARGs. The number of main antibiotic-resistant bacteria (e.g., Prevotella, Ruminococcus) decreased by 74.9 %, while their potential antagonistic bacteria (e.g., Bacillus, Pseudomonas) increased by 128.7 %. The number of antibiotic-resistant pathogenic bacteria (e.g., Selenomonas, Paenalcaligenes) decreased by 88.3 %, and the average number of ARGs carried by each human pathogenic bacterial genus declined by 55.8 %. BSF larvae gut microbiota (e.g., Clostridium butyricum, C. bornimense) could help reduce the risk of multidrug-resistant pathogens. These results provide insight into a novel approach to mitigate multidrug resistance from the animal industry in the environment by using insect technology combined with composting, in particular in light of the global "One Health" requirements.

Study effect and mechanism of levofloxacin on the neurotoxicity of Rana nigromaculata tadpoles exposed to imidacloprid based on the microbe-gut-brain axis

Aquatic organisms may be simultaneously exposed to antibiotics and pesticides. After levofloxacin (LVFX), imidacloprid (IMI) exposure and co-exposure at environmental levels, we found LVFX and IMI had antagonistic effect on the neurotoxicity of tadpoles. IMI-induced neurotoxicity on tadpoles can be explained by oxidative stress and hormone levels in some degree. By regulating ornithine, l-asparagine, putrescine and tryptamine in the intestine, LVFX affected glutathione metabolism, arginine and proline metabolism, alanine, aspartate and glutamate metabolism, tyrosine metabolism and aminoacyl tRNA biosynthesis, so then eased the neurotoxicity caused by IMI. More interestingly, Fusobacteriota and Cetobacterium might play an important role on easing the neurotoxicity caused by IMI. In addition, LVFX might have a laxation effect on the increased relative abundance of Bacteroidota caused by IMI. In conclusion, IMI not only affected oxidative stress and hormone levels in the brain, but also affected the synthesis of neurotransmitters in the intestine by regulating intestinal microbiota. In LVFX and IMI co-exposed groups, LVFX alleviated the neurotoxicity caused by IMI through regulating the intestinal microbiota, showing as an antagonistic effect. Our results provided a new perspective for aquatic ecological risk assessment under co-exposure of antibiotics and pesticides.

The Use of Probiotics during Rearing of Hermetia illucens: Potential, Caveats, and Knowledge Gaps

Given the novelty of the industrial production of the edible insects sector, research has primarily focused on the zootechnical performances of black soldier fly larvae (BSFL) in response to different substrates and rearing conditions as a basis to optimize yield and quality. However recently, research has started to focus more on the associated microbes in the larval digestive system and their substrates and the effect of manipulating the composition of these communities on insect performance as a form of microbiome engineering. Here we present an overview of the existing literature on the use of microorganisms during rearing of the BSFL to optimize the productivity of this insect. These studies have had variable outcomes and potential explanations for this variation are offered to inspire future research that might lead to a better success rate for microbiome engineering in BSFL.

Microplastics existence intensified bloom of antibiotic resistance in livestock feces transformed by black soldier fly

Efficient degradation of residual antibiotics in livestock and poultry feces by black soldier flies (BSFs) has been widely reported. Nevertheless, the effects of widely detected microplastics in feces on the dynamic reduction of antibiotics and the transfer of gut bacterial resistome remain unclear. In this study, red fluorescence-labeled microplastics are observed to be abundantly distributed in BSFs gut, which caused epithelial cell damage along with gut peristalsis and friction, thereby releasing reactive oxygen species and activating the antioxidant enzyme system. In addition, they result in not only in inflammatory cytokine release to induce gut inflammation, but fecal hardening because of mucus released from the BSFs, thereby hindering organic mineralization and antibiotic degradation. Besides, the gut pathogenic bacteria easily obtain growth energy and crowded out ecological niches by reducing nitrate produced by inflammatory host cells to nitrite with nitrate reductase. Consequently, linear discriminant analysis effect size and detrended correspondence analysis found that microplastic intake significantly reshape the microbial community structure and cause the significant reduction of several important organic-decomposing bacteria and probiotics (e.g., Pseudomonadales, Coriobacteriales, Lachnospirales, and Ruminococcaceae). In addition, a large number of pathogenic bacteria (e.g., Enterococcaceae, Hungateiclostridiaceae, and Clostridia) are enriched in feces and BSFs gut. Weighted correlation network analysis and bubble diagram analysis indicate that microplastic intake intensified gut colonization of pathogenic bacteria carrying antibiotic-resistant genes/mobile genetic elements, driving the bloom of antibiotic resistance in transformed fecal piles. Therefore, microplastics in feces should be isolated as much as possible before insect transformation.

Two low-toxic Klebsiella pneumoniae strains from gut of black soldier fly Hermetia illucens are multi-resistance to sulfonamides and cadmium

In recent years, pollution of antibiotics and heavy metal has often been reported in organic wastes. Saprophytic insects have been recorded as biological control agents in organic waste management. During organic waste conversion, the intestinal bacteria of the saprophytic insects play an important role in digestion, physiology, immunity and prevention of pathogen colonization. Black soldier fly (BSF) Hermetia illucens has been widely used as saprophytic insects and showed tolerance to sulfonamides (SAs) and cadmium (Cd). Diversity and changes in gut microbiota of black soldier fly larvae (BSFL) were evaluated through 16S rRNA high-throughput sequencing, and a decrease in diversity of gut microbiota along with an increase in SAs stress was recorded. Major members identified were Actinomycetaceae, Enterobacteriaceae, and Enterococcaceae. And fourteen multi-resistance Klebsiella pneumoniae strains were isolated. Two strains BSFL7-B-5 (from middle midgut of 7-day BSFL) and BSFL11-C-1 (from posterior midgut of 11-day BSFL) were found to be low-toxic and multi-resistance. The adsorption rate of SAs in 5 mg/kg solutions by these two strains reached 65.2% and 61.6%, respectively. Adsorption rate of Cd in 20 mg/L solutions was 77.2% for BSFL7-B-5. The strain BSFL11-C-1 showed higher than 70% adsorption rates of Cd in 20, 30 and 40 mg/L solutions. This study revealed that the presence of multi-resistance bacterial strains in the gut of BSFL helped the larvae against SAs or Cd stress. After determining how and where they are used, selected BSFL gut bacterial strains might be utilized in managing SAs or Cd contamination at suitable concentrations in the future.

Transmission of tetracycline resistance genes and microbiomes from manure-borne black soldier fly larvae frass to rhizosphere soil and pakchoi endophytes

Manure treatment with black soldier fly larvae (BSFL) and BSFL frass application in crop land is a sustainable strategy; however, whether residual antibiotic resistance genes (ARGs) and their transmission risk are related to the manure BSFL treatment process is still unknown. In this paper, the effect of BSFL addition density on residual tetracycline resistance genes (TRGs) and transmission from frass to pakchoi was determined. The results showed that BSFL frass can provide sufficient nutrients for growth, improve the economic value of pakchoi, and reduce the risk of transmission of TRGs in chicken manure regardless of BSFL density. The potential hosts of the TRGs we detected were found in BSFL frass (Oblitimonas and Tissierella), rhizosphere soil (Mortierella and Fermentimonas), and pakchoi endophytes (Roseomonas). The present study concluded that BSFL frass produced by adding 100 BSFL per 100 g of chicken manure has the advantages of high value and low risk. These findings will provide important strategic guidance for animal manure disposal and theoretical support for preventing the transmission of TRGs in BSFL applications.

Reciprocal interactions between anthropogenic stressors and insect microbiota

Insects play many important roles in nature due to their diversity, ecological role, and impact on agriculture or human health. They are directly influenced by environmental changes and in particular anthropic activities that constitute an important driver of change in the environmental characteristics. Insects face numerous anthropogenic stressors and have evolved various detoxication mechanisms to survive and/or resist to these compounds. Recent studies highligted the pressure exerted by xenobiotics on insect life-cycle and the important role of insect-associated bacterial microbiota in the insect responses to environmental changes. Stressor exposure can have various impacts on the composition and structure of insect microbiota that in turn may influence insect biology. Moreover, bacterial communities associated with insects can be directly or indirectly involved in detoxification processes with the selection of certain microorganisms capable of degrading xenobiotics. Further studies are needed to assess the role of insect-associated microbiota as key contributor to the xenobiotic metabolism and thus as a driver for insect adaptation to polluted habitats.

Hermetia illucens L. larvae-associated intestinal microbes reduce the transmission risk of zoonotic pathogens in pig manure

Black soldier fly (BSF) larvae are considered a promising biological reactor to convert organic waste and reduce the impact of zoonotic pathogens on the environment. We analysed the effects of BSF larvae on Staphylococcus aureus and Salmonella spp. populations in pig manure (PM), which showed that BSF larvae can significantly reduce the counts of the associated S. aureus and Salmonella spp. Then, using a sterile BSF larval system, we validated the function of BSF larval intestinal microbiota in vivo to suppress pathogens, and lastly, we isolated eight bacterial strains from the BSF larval gut that inhibit S. aureus. Results indicated that functional microbes are essential for BSF larvae to antagonise S. aureus. Moreover, the analysis results of the relationship between the intestinal microbiota and S. aureus and Salmonella spp. showed that Myroides, Tissierella, Oblitimonas, Paenalcalignes, Terrisporobacter, Clostridium, Fastidiosipila, Pseudomonas, Ignatzschineria, Savagea, Moheibacter and Sphingobacterium were negatively correlated with S. aureus and Salmonella. Overall, these results suggested that the potential ability of BSF larvae to inhibit S. aureus and Salmonella spp. present in PM is accomplished primarily by gut‐associated microorganisms.

Morphometric Characteristic of Black Soldier Fly (Hermetia illucens) · Wuhan Strain and Its Egg Production Improved by Selectively Inbreeding

The use of black soldier fly (BSF) larvae to recycle various organic materials while producing biomass for use as feed is well established. Variety selection is important from the perspective of application. In the current study, morphometric and life-history traits of a Wuhan-domesticated BSF colony (Wuhan strain) were compared to those of a 'selectively inbred' population (inbred strain, inbred for 10 generations). In terms of morphological characteristics, the results showed that both strains had dichoptic compound eyes, club-shaped antennae, blue halters, and blue-green metallic luster wings with a hexagon discal cell. In both strains, the body and wing length of female adults were slightly larger than those of male adults. The first four larval stages of the BSF occurred rapidly (1-12 days) with transitions across stages resulting in doubling of size for both populations. Selective inbreeding did not alter the life-history traits of the larval exuviate stage in terms of age, size, weight, and feed reduction rate. Overall egg production for the inbred strain was significantly higher (1.5 times greater) than the Wuhan strain. This is explained by increased adult emergence and individual oviposition performance. It was speculated that inbreeding improved the reproductive success of inbred adult female offspring and selection process steadied it. The findings indicate that selective inbreeding could enhance overall oviposition performance and provide a strategy to selectively breed BSF with high egg production for future applications.

Enhanced performance of microbial fuel cell with electron mediators from tetracycline hydrochloride degradation

Tetracycline hydrochloride (TCH) is a typical antibiotic pollutant with high toxicity and persistence. The degradation of TCH and the generation of the associated electron mediator in a dual chamber microbial fuel cells (MFCs) were studied. The results of liquid chromatography revealed that TCH could be effectively removed (>93%) in MFCs mode. The maximum COD removal was 88.14 ± 1.47% in MFCs while it was 69.57 ± 1.36% in open circuit MFCs. According to cyclic voltammetry, the presence of the relevant redox peaks clearly suggested that the intermediates from TCH degradation could act as endogenous electron mediator. The highest power density of 120.02 ± 2.76 mW/m² and the lowest internal resistance of 18.68 Ω were achieved in MFC with 2 mg/L of TCH. Microbial community analysis illustrated that Bacteroides, Comamonas, Clostridium_sensu_stricto, Desulfovibrio and Geobacter were enriched and played a dominant role in TCH degradation and power generation. Electrochemical active bacteria had certain tolerance to TCH and the inhibiting threshold value of TCH was below 5 mg/L. This study provided a new thinking that low concentration of TCH could produce electron mediators to improve the performance of MFC system.

Black soldier fly larvae effectively degrade lincomycin from pharmaceutical industry wastes

Lincomycin fermentation residues (LFR) are the byproducts from the pharmaceutical industry, and contain high concentrations of antibiotics that could pose a threat to the environment. Here, we report that black soldier fly larvae (BSFL) and associated microbiota can effectively degrade LFR and accelerate the degradation of lincomycin in LFR. The degradation rate of lincomycin in LFR can reach 84.9% after 12 days of BSFL-mediated bioconversion, which is 3-fold greater than that accomplished with natural composting. The rapid degradation was partially carried out by the BSFL-associated microbiota, contributing 22.0% of the degradation in the final composts. Based on microbiome analysis, we found that the structure of microbiota from both BSFL guts and BSFL composts changed significantly during the bioconversion, and that several bacterial genera were correlated with lincomycin degradation. The roles of the associated microbiota in the degradation were further verified by the ability of two larval intestinal bacterial isolates and one bacterial isolate from BSFL composts to lincomycin degradation. The synergy between BSFL and the isolated strains resulted in a 2-fold increase in degradation compared to that achieved by microbial degradation alone. Furthermore, we determined that the degradation was correlated with the induction of several antibiotic resistant genes (ARGs) associated with lincomycin degradation in larval guts and BSFL composts. Moreover, the environmental conditions in the BSFL composts were found to be conducive to the degradation. In conclusion, these findings demonstrate that the BSFL-mediated bioconversion of LFR could effectively reduce residual lincomycin and that the associated microbiota play crucial roles in the process.

A comprehensive review on biodegradation of tetracyclines: Current research progress and prospect

The release of tetracyclines (TCs) in the environment is of significant concern because the residual antibiotics may promote resistance in pathogenic microorganisms, and the transfer of antibiotic resistance genes poses a potential threat to ecosystems. Microbial biodegradation plays an important role in removing TCs in both natural and artificial systems. After long-term acclimation, microorganisms that can tolerate and degrade TCs are retained to achieve efficient removal of TCs under the optimum conditions (e.g. optimal operational parameters and moderate concentrations of TCs). To date, cultivation-based techniques have been used to isolate bacteria or fungi with potential degradation ability. Moreover, the biodegradation mechanism of TCs can be unveiled with the development of chemical analysis (e.g. UPLC-Q-TOF mass spectrometer) and molecular biology techniques (e.g. 16S rRNA gene sequencing, multi-omics sequencing, and whole genome sequencing). In this review, we made an overview of the biodegradation of TCs in different systems, refined functional microbial communities and pure isolates relevant to TCs biodegradation, and summarized the biodegradation products, pathways, and degradation genes of TCs. In addition, ecological risks of TCs biodegradation were considered from the perspectives of metabolic products toxicity and resistance genes. Overall, this article aimed to outline the research progress of TCs biodegradation and propose future research prospects.

Characteristics and mechanisms of ciprofloxacin degradation by black soldier fly larvae combined with associated intestinal microorganisms

Antibiotics are challenging to degrade and are excreted by livestock which results in environmental pollution. In this paper, we demonstrated that environmentally friendly manure bioremediation performed by black soldier fly larvae (BSFL) is a wise alternative, which could effectively degrade ciprofloxacin (CIP) by approached 85.48% in artificial diet and 84.22% in poultry manure within 12 days. They are up to 2.5-4.0 fold more than that achieved by natural fermentation. The five CIP-degrading strains were isolated from the larval gut, two of which, named by Klebsiella pneumoniae BSFLG-CIP1 and Proteus mirabilis BSFLG-CIP5, could degraded CIP by nearly 98.22% and 97.83% in vitro, respectively. When the intestinal isolates were re-inoculated to sterile BSFL system, the degradation level significantly increased up to 82.38%, comparing with the sterile BSFL system (21.76%). It is proved that the larvae intestinal microbiota might carry out this highly-efficient CIP-degradation. Furthermore, seven possible metabolites were identified for CIP-degradation in vitro, and they were referring three main potential degrading mechanisms of hydroxylize, piperazine ring substitute and cleavage, and quinoline ring cleavage. In conclusion, the present study may provide a strategy to reduce antibiotics pollution in animal waste through bioremediation with BSFL and adjusted intestinal microbes.

Rice straw particles covered with Brevundimonas naejangsanensis DD1 cells can synergistically remove doxycycline from water using adsorption and biotransformation

Doxycycline (DC) is a second generation tetracycline antibiotic and its occurrence in the aquatic environment due to the discharge of municipal and agricultural wastes has called for technologies to effectively remove DC from water. The objective of the study was to characterize the synergistic benefits of adsorption and biotransformation in removing DC from water using rice straw particles (RSPs) covered with DC degrading bacteria, Brevundimonas naejangsanensis strain DD1. First, optimal experimental conditions were identified for individual processes, i.e., hydrolysis, adsorption, and biotransformation, in terms of their performance of removing DC from water. Then, synergistic effects between adsorption and biotransformation were demonstrated by adding DD1-covered RSPs (DD1-RSPs) to DC-containing solution. Results suggest that DC was quickly adsorbed onto RSPs and the adsorbed DC was subsequently biotransformed by the DD1 cells on RSPs. The adsorption of DC to DD1-RSPs can be well described using the pseudo-second-order kinetics and the Langmuir isotherm. The DD1 cells on RSPs converted DC to several biotransformation products through a series of demethylation, dehydration, decarbonylation, and deamination. This study demonstrated that adsorption and biotransformation could work synergistically to remove DC from water.

A sustainable and economic strategy to reduce risk antibiotic resistance genes during poultry manure bioconversion by black soldier fly Hermetia illucens larvae: Larval density adjustment

Black soldier fly (Hermetia illucens) larvae (BSFL) are common insects that are known for bioconversion of organic waste into a sustainable utilization resource. However, a strategy to increase antibiotic resistance gene (ARG) elimination in sustainable and economic ways through BSFL is lacking. In the present study, different larval densities were employed to assess the mcr-1 and tetX elimination abilities, and potential mechanisms were investigated. The application and economic value of each larval density were also analyzed. The results showed that the 100 larvae cultured in 100 g of manure group had the best density because the comprehensive disadvantage evaluation ratio was the lowest (14.97%, good bioconversion manure quality, low ARG deposition risk and reasonable larvae input cost). Further investigation showed that mcr-1 could be significantly decreased by BSFL bioconversion (4.42 ×10⁷ copies/g reduced to 4.79 ×10⁶-2.14 ×10⁵ copies/g)(P＜0.05); however, mcr-1 was increasingly deposited in the larval gut with increasing larval density. The tetX abundance was stabilized by BSFL bioconversion, except that the abundance at the lowest larval density increased (1.22 ×10¹⁰ copies/g increase, 34-fold). Escherichia was the host of mcr-1 and tetX in all samples, especially in fresh manure; Alcaligenes was the host of tetX in bioconversion manure; and the abundance of Alcaligenes was highly correlated with the pH of bioconversion manure. The pH of bioconversion manure was extremely correlated with the density of larvae. Klebsiella and Providencia were both hosts of tetX in the BSF larval gut, and Providencia was also the host of mcr-1 in the BSF larval gut. The density of larvae influenced the bioconversion manure quality and caused the ARG host abundance to change to control the abundance of ARGs, suggesting that larval density adjustment was a useful strategy to manage the ARG risk during BSFL manure bioconversion.

Degradation of Tetracycline Hydrochloride by Cu-Doped MIL-101(Fe) Loaded Diatomite Heterogeneous Fenton Catalyst

In this work, the combination of high surface area diatomite with Fe and Cu bimetallic MOF material catalysts (Fe_0.25Cu_0.75(BDC)@DE) were synthesized by traditional solvothermal method, and exhibited efficient degradation performance to tetracycline hydrochloride (TC). The degradation results showed: Within 120 min, about 93% of TC was degraded under the optimal conditions. From the physical–chemical characterization, it can be seen that Fe and Cu play crucial roles in the reduction of Fe³⁺ because of their synergistic effect. The synergistic effect can not only increase the generation of hydroxyl radicals (•OH), but also improve the degradation efficiency of TC. The Lewis acid property of Cu achieved the pH range of reaction system has been expanded, and it made the material degrade well under both neutral and acidic conditions. Loading into diatomite can reduce agglomeration and metal ion leaching, thus the novel catalysts exhibited low metal ion leaching. This catalyst has good structural stability, and less loss of performance after five reaction cycles, and the degradation efficiency of the material still reached 81.8%. High performance liquid chromatography–mass spectrometry was used to analyze the degradation intermediates of TC, it provided a deep insight of the mechanism and degradation pathway of TC by bimetallic MOFs. This allows us to gain a deeper understanding of the catalytic mechanism and degradation pathway of TC degradation by bimetallic MOFS catalysts. This work has not only achieved important progress in developing high-performance catalysts for TC degradation, but has also provided useful information for the development of MOF-based catalysts for rapid environmental remediation.

Effects of various antibiotics on aerobic nitrogen removal and antibiotic degradation performance: Mechanism, degradation pathways, and microbial community evolution

Little information about the selective stress of various antibiotics and how they influence different stages of aerobic nitrogen removal is available. A long-term aerobic nitrogen removal-moving bed biofilm reactor was established by the inoculation of Achromobacter sp. JL9, capable of heterotrophic nitrification and aerobic denitrification, and aerobic activated sludge. The nitrogen removal and antibiotic degradation performances of various antibiotics were then measured. High total nitrogen (91.83% and 91.51%) removal efficiencies were achieved with sulfamethoxazole or no antibiotics, and lower efficiencies were observed with other antibiotics (trimethoprim, teicoplanin, and ciprofloxacin). These results suggest that various antibiotics have different selective inhibitory effects on aerobic nitrogen removal. Additionally, all antibiotics were partly degraded; proposed degradation pathways according to the detected intermediates included ring-opening, S-N bond cleavage, amination, hydroxylation, and methylation. High-throughput sequencing indicated that aerobic denitrifying, recalcitrant pollutant degrading, and antibiotic-resistant bacteria dominate during the community evolution process.

Characteristics of tylosin and enrofloxacin degradation in swine manure digested by black soldier fly (Hermetia illucens L.) larvae

Black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) larvae (BSF larvae or BSFL) offer an environmental-friendly method for degrading antibiotics, such as tylosin (TYL) and enrofloxacin (EF), in swine manure. This study examined the impact of temperature on this process, role of associated microbes, dynamics of resistant genes, and a description of the microbial community associated with the BSF larval gut, how microbes isolated from the BSF larval gut as inoculants impact the process as well as enhance antibiotic digestion, and finally a quantification of antibiotics in BSF larvae fed manure with TYL or EF. Antibiotic degradation in manure was optimized at 28 °C with at least 10% greater than 23 °C and 37 °C. More than 40% reduction in TYL and EF concentrations in the manure occurred when BSF larval gut associated microbes were present. Furthermore, DNA extracted from the gut of non-sterile BSF larvae fed manure with TYL or EF indicated at least two 2^-△△Ct fold increase in antibiotic resistance genes for TYL and EF. We identified 250, 4, and 16 unique operational taxa for larvae fed control manure and manure with either TYL or EF. Intestinal microbes isolated from non-sterile larvae fed manure with TYL or EF, were identified, cultured, and examined for their ability to degrade TYL and EF in Luria-Bertani (LB) medium. Three strains (two strains of Enterococcus faecalis and one strain of Proteus mirabilis) resulted in at least 50% TYL or EF degradation within 96 h. Sterile BSF larvae inoculated with P. mirabilis recovered >60% of the degradation ability exhibited by non-sterile larvae. Finally, no TYL residuals were found in 14-d-old larvae, prepupae, or pupae of BSF immatures fed manure containing these antibiotics. While ∼65 μg/g and ∼20 μg/g of EF were found in larval contents and pupal exoskeleton, respectively.

Staphylococcus aureus in Substrates for Black Soldier Fly Larvae (Hermetia illucens) and Its Dynamics during Rearing

Black soldier fly larvae (BSFL; Hermetia illucens) are promising insects for the conversion of organic waste streams into valuable biomolecules. Such waste streams can contain foodborne pathogens. To assess this risk factor, this study evaluated the presence of Staphylococcus aureus in waste streams as a substrate ingredient for BSFL production as well as in the rearing process. First, the general microbiological quality and the occurrence of S. aureus were investigated for different waste streams. Staphylococcus aureus was abundantly present. Control of pH and water activity should avoid pathogens, which cannot grow in single-substrate ingredients, redeveloping when mixing streams for optimal substrate conditions for BSFL production. Next, it was investigated whether S. aureus present in the substrate was ingested and/or eradicated by BSFL. In inoculation trials, with S. aureus added to chicken feed as the substrate at 3 or 7 log CFU/g, the larvae showed a reducing effect on S. aureus. After 6 days, S. aureus counts were below the detection limit (2.0 log CFU/g) in all larvae samples and decreased in the substrate to <2.0 and <3.1 log CFU/g for inoculation levels of 3 and 7 log CFU/g, respectively. While this is promising, it is still recommended to monitor and control this pathogen in BSFL rearing. Intriguingly, screening of antimicrobial activity of dominant microorganisms associated with BSFL showed a clear activity of Trichosporon isolates against S. aureus. Future research should explore whether Trichosporon, which is frequently observed in BSFL, plays a role in controlling specific microorganisms, such as S. aureus. IMPORTANCE Given the increasing need for (more sustainable) methods to upcycle organic waste streams, the interest to rear insects, like black soldier fly larvae (BSFL), on such streams is increasing. This study reveals that S. aureus is abundantly present in such waste streams, which might be a point of attention for insect producers. At the same time, it reveals that when S. aureus was inoculated in chicken feed as the substrate, it was not detected in the larvae and was reduced in the substrate after 6 days. Future inoculation trials should investigate whether this reduction is substrate dependent or not. Toward the future, the role of the BSFL microbiota in controlling intestinal bacterial community homeostasis should be explored, because one of the dominant microorganisms associated with BSFL, Trichosporon spp., showed clear activity against S. aureus.

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.

Identification of three metallothioneins in the black soldier fly and their functions in Cd accumulation and detoxification

The black soldier fly (BSF) Hermetia illucens has a strong tolerance to cadmium stress. This helps to use BSF in entomoremediation of heavy metal pollution. Rich metallothionein (MT) proteins were thought to be important for some insects to endure the toxicity of heavy metal. We identified and characterized three MTs genes in BSF (BSFMTs), including BSFMT1, BSFMT2A, and BSFMT2B. Molecular modeling was used to predict metal binding sites. Phylogenetic analysis was used to identify gene families. Overexpression of the recombinant black soldier fly metallothioneins was found to confer Cd tolerance in Escherichia coli. Finally, functions of BSFMTs in BSF were explored through RNA interference (RNAi). RNAi results of BSFMT2B showed that the larval fresh weight decreased significantly, and the larvae mortality increased significantly. This study suggests that BSFMTs have important properties in Cd detoxification and tolerance in BSF. Further characterization analyses of physiological function about metallothioneins are necessary in BSF and other insects.

Biotransformation of doxycycline by Brevundimonas naejangsanensis and Sphingobacterium mizutaii strains

The fate of doxycycline (DC), a second generation tetracycline antibiotic, in the environment has drawn increasing attention in recent years due to its wide usage. Little is known about the biodegradability of DC in the environment. The objective of this study was to characterize the biotransformation of DC by pure bacterial strains with respect to reaction kinetics under different environmental conditions and biotransformation products. Two bacterial strains, Brevundimonas naejangsanensis DD1 and Sphingobacterium mizutaii DD2, were isolated from chicken litter and characterized for their biotransformation capability of DC. Results show both strains rely on cometabolism to biotransform DC with tryptone as primary growth substrate. DD2 had higher biotransformation kinetics than DD1. The two strains prefer similar pHs (7 and 8) and temperature (30 °C), however, they exhibited opposite responses to increasing background tryptone concentration. While hydrolysis converted DC to its isomer or epimer, the two bacterial strains converted DC to various biotransformation products through a series of demethylation, dehydration, decarbonylation and deamination. Findings from the study can be used to better predict the fate of DC in the environment.

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.

Characteristics and nutrient function of intestinal bacterial communities in black soldier fly (Hermetia illucens L.) larvae in livestock manure conversion

The potential utility of black soldier fly larvae (BSFL) to convert animal waste into harvested protein or lipid sources for feeding animal or producing biodiesel provides a new strategy for agricultural waste management. In this study, the taxonomic structure and potential metabolic and nutrient functions of the intestinal bacterial communities of BSFL were investigated in chicken and swine manure conversion systems. Proteobacteria, Firmicutes and Bacteroidetes were the dominant phyla in the BSFL gut in both the swine and chicken manure systems. After the larvae were fed manure, the proportion of Proteobacteria in their gut significantly decreased, while that of Bacteroidetes remarkably increased. Compared with the original intestinal bacterial community, approximately 90 and 109 new genera were observed in the BSFL gut during chicken and swine manure conversion, and at least half of the initial intestinal genera found remained in the gut during manure conversion. This result may be due to the presence of specialized crypts or paunches that promote microbial persistence and bacteria-host interactions. Ten core genera were found in all 21 samples, and the top three phyla among all of the communities in terms of relative abundance were Proteobacteria, Firmicutes and Bacteroidetes. The nutrient elements (OM, TN, TP, TK and CF) of manure may partly affect the succession of gut bacterial communities with one another, while TN and CF are strongly positively correlated with the relative abundance of Providencia. Some bacterial taxa with the reported ability to synthesize amino acids, Rhizobiales, Burkholderia, Bacteroidales, etc., were also observed in the BSFL gut. Functional analysis based on genes showed that intestinal microbes potentially contribute to the nutrition of BSFL and the high-level amino acid metabolism may partly explain the biological mechanisms of protein accumulation in the BSFL body. These results are helpful in understanding the biological mechanisms of high-efficiency nutrient conversion in BSFL associated with intestinal microbes.

Black soldier fly reared on pig manure: Bioconversion efficiencies, nutrients in the residual material, greenhouse gas and ammonia emissions

There is an increased interest for using insects, such as the black soldier fly, to treat surplus manure and upcycle nutrients into the food system. Understanding the influence that BSFL have on nutrient flows and nutrient losses during manure bioconversion is key for sustainability assessments. Here we quantified and compared nutrient balances, nutrient levels in residual materials and emissions of greenhouse gases and ammonia between manure incubated with black soldier fly larvae (BSFL) and manure without BSFL, during a 9-day experimental period. We obtained high analytical recoveries, ranging between 95 and 103%. We found that of the pig manure supplied, 12.5% of dry matter (DM), 13% of carbon, 25% of nitrogen, 14% of energy, 8.5% of phosphorus and 9% of potassium was stored in BSFL body mass. When BSFL were present, more carbon dioxide (247 vs 148 g/kg of DM manure) and ammonia-nitrogen (7 vs 4.5 g/kg of DM manure) emitted than when larvae were absent. Methane, which was the main contributor to greenhouse gas emissions, was produced at the same levels (1.3 vs 1.1 g/kg of DM manure) in both treatments, indicating the main role that manure microbial methane emissions play. Nitrous oxide was negligible in both treatments. The uptake of nutrients by the larvae and the higher carbon dioxide and ammonia emissions modified the nutrient composition of the residual material substantially relative to the fresh manure. Our study provides a reliable basis to quantify the environmental impact of using BSFL in future life cycle assessments.

Feed-additive of bioengineering strain with surface-displayed laccase degrades sulfadiazine in broiler manure and maintains intestinal flora structure

Sulfonamide antibiotics (SAs) are excreted into the ecosystem unchanged through feces and urine because of their low adsorption and degradation in the guts of humans and animals. In this study, a novel whole-cell biocatalyst with fungal laccase on the cell surface of Escherichia coli Nissle 1917 was developed to degrade sulfadiazine (SDZ). Engineered strain EcN-IL showed laccase enzyme activity of 2 ± 1 U/mg dry weight of cell and degraded 37 ± 1% of SDZ at temperature 40 °C and pH 5 within 3 h in vitro. Strain EcN-IL with 500 mg/kg of SDZ was employed as a food supplement to feed chicken broilers, which can reduce the residue of SDZ in broiler manure by 58 ± 2% and also reduced dysbiosis of the gut microbiota due to overuse of antibiotics. The genetically engineered EcN-IL has laid a foundation for degrading SDZ in broilers and their manure.

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.

The changes of antioxidant system and intestinal bacteria in earthworms (Metaphire guillelmi) on the enhanced degradation of tetracycline

Tetracycline (TC) in soil severely imperils food security and ecosystem function. Metaphire guillelmi is a common species in farmland. It could impact the degradation of antibiotics. However, how it affects is rarely unknown. Hence, the present study aimed to investigate the effects of M. guillelmi on the TC degradation in soil and the changes of the antioxidant system and intestinal bacteria in M. guillelmi. The treatments that M. guillelmi was inoculated on soil contaminated with different TC concentrations were contrasted with those without M. guillelmi. After 21 days, the degradation rate of TC significantly increased by 13.70%, 18.14% and 29.01% at 10, 50 and 100 mg kg ^-1 TC dose, respectively, due to the inoculation of M. guillelmi. The half-life of TC was also shortened nearly by 1/3 to 2/3. Superoxide dismutase (SOD) increased in a dose-dependent manner with the increase of TC concentration on the 7th and 14th day. Catalase (CAT) and glutathione S-transferase (GST) presented an inverted U-shaped dose response on the 7th day, and the peak of enzyme activities occurred at TC concentration of 0.1, 1 mg kg ^-1 (CAT) and 0.1 mg kg ^-1 (GST). Malondialdehyde (MDA) contents did not change significantly. At the phylum level, only Verrucomicrobia significantly decreased under 1 mg kg ^-1 and 100 mg kg ^-1 TC dose. Genus Paracoccus, Singulisphaera, Acinetobacter and Bacillus significantly increased and became the dominant bacterium during the TC degradation. Overall, the antioxidant system and intestinal bacteria of M. guillelmi were affected by the different concentrations of TC pollution, which provided new ideas for the research of mechanism of TC degradation by earthworms in the future.

Material flow analysis and life cycle assessment of food waste bioconversion by black soldier fly larvae (Hermetia illucens L.)

This study provided a systematic analysis on material flow and environmental impacts of a food waste (FW) bioconversion plant using black soldier fly larvae (BSFL), with a daily capacity of 15 tons of FW (wet weight). Food waste feed (FWF) used for BSFL bioconversion consisted of 80% FW (collected from households, restaurants, and canteens) and 20% rice hull powder. Material flow analysis conducted on a dry weight basis showed that 6% of FWF was transformed into BSF pre-pupae, 51% was stored in matured compost, and 43% was emitted to the air. Emissions of high environmental concern such as methane, nitrous oxide and ammonia (NH₃) were sampled and quantified by laboratory analysis. The life cycle assessment revealed that the overall impact was 17.36 kg CO₂-eq/t FW for global warming potential, 5.54 kg SO₂-eq/t FW for acidification, 24.05 mol N-eq/t FW for terrestrial eutrophication, 0.54 kg N-eq NH₃/t FW for marine eutrophication, and 0.18 kg PM_2.5-eq/t FW of particulate matter up to 2.5 μm diameter. Moreover, emissions from post-composting, energy consumptions of drying and chemical fertilizer substitution ratio were detected by contribution analysis as the main contributors to those impacts. Finally, sensitivity analysis indicated that the substitution ratio of mineral fertilizer and protein feed as well as energy consumption were the most influential parameters, therefore control of the post-composting process of residual material should be closely monitored because it was responsible for significant environmental load caused by N-related emissions.

Changes in gut bacterial communities and the incidence of antibiotic resistance genes during degradation of antibiotics by black soldier fly larvae

As a saprophytic insect, the black soldier fly can digest organic waste efficiently in an environmentally friendly way. However, the ability and efficiency of this insect, and the microbial mechanisms involved, in the degradation of antibiotics are largely uncharacterized. To obtain further details during the degradation of OTC (oxytetracycline) by black soldier fly larvae (larvae), the changes in intestinal bacterial communities were examined. Both ARGs (antibiotic resistance genes) and MGEs (mobile genetic elements) were found within the larval guts. At the end of the degradation period, 82.7%, 77.6% and 69.3% of OTC was degraded by larvae when the initial concentrations were 100, 1000 and 2000 mg kg^-1 (dry weight), respectively, which was much higher than the degradation efficiencies (19.3-22.2%) without larvae. There was no obvious effect of OTC on the development of the larvae. Although the larval gut microorganisms were affected by OTC, they adapted to the altered environment. Enterococcus, Ignatzschineria, Providencia, Morganella, Paenalcaligenes and Actinomyces in the gut responded strongly to antibiotic exposure. Interestingly, numerous ARGs (specifically, 180 ARGs and 10 MGEs) were discovered, and significantly correlated with those of both integron-integrase gene and transposases in the larval gut. Of all the detected ARGs, tetracycline resistance genes expressed at relatively high levels and accounted for up to 67% of the total ARGs. In particular, Enterococcus, Ignatzschineria, Bordetella, Providencia and Proteus were all hosts of enzymatic modification genes of tetracycline in the guts that enabled effective degradation of OTC. These findings demonstrate that OTC can be degraded effectively and prove that the bioremediation of antibiotic contamination is enhanced by larvae. In addition, the abundance of ARGs and MGEs formed should receive attention and be considered in environmental health risk assessment systems.

Tetracycline degradation by Klebsiella sp. strain TR5: Proposed degradation pathway and possible genes involved

Microorganisms with high tetracycline (TC) degradation efficiencies are required for biological processes for TC-containing wastewater treatment. With multiple enrichment cultures, a TC-degrading strain TR5 was isolated from chicken manure mixture in a large broiler farm, which was identified as Klebsiella pneumoniae by 16S rRNA gene sequencing and biochemical properties. Strain TR5 could degrade TC quickly (∼90% within 36 h) with the initial TC concentration of 200 mg/L under optimized conditions via single-factor experiment coupled with RSM. Strain TR5 could detoxify TC and generate much less toxic products as long as cultured more than one day. Three TC-degrading pathways were proposed based on 8 possible products. A transformant containing a plasmid from TR5 acquired TC-degrading ability, indicating that TC-degrading genes were located on this plasmid. Complete sequencing of pYK5 showed that isomerase-, oxidoreductase-, and transferases-encoding genes were found and were inferred to be involved in TC degradation. TR5 may not degrade TC completely and it can utilize some carbon-containing compounds derived from TC via the effect of formylglutathione hydrolase-encoding gene. Our findings showed that strain TR5 could be a promising agent for wastewater treatment, and genes involved in TC degradation are worthy of further investigations for enzyme preparations development.