The Core Gut Microbiome of Black Soldier Fly (Hermetia illucens) Larvae Raised on Low-Bioburden Diets

Abstract

An organism's gut microbiome handles most of the metabolic processes associated with food intake and digestion but can also strongly affect health and behavior. A stable microbial core community in the gut provides general metabolic competences for substrate degradation and is robust against extrinsic disturbances like changing diets or pathogens. Black Soldier Fly larvae (BSFL; Hermetia illucens) are well known for their ability to efficiently degrade a wide spectrum of organic materials. The ingested substrates build up the high fat and protein content in their bodies that make the larvae interesting for the animal feedstuff industry. In this study, we subjected BSFL to three distinct types of diets carrying a low bioburden and assessed the diets' impact on larval development and on the composition of the bacterial and archaeal gut community. No significant impact on the gut microbiome across treatments pointed us to the presence of a predominant core community backed by a diverse spectrum of lowabundance taxa. Actinomyces spp., Dysgonomonas spp., and Enterococcus spp. as main members of this community provide various functional and metabolic skills that could be crucial for the thriving of BSFL in various environments. This indicates that the type of diet could play a lesser role in guts of BSFL than previously assumed and that instead a stable autochthonous collection of bacteria provides the tools for degrading of a broad range of substrates. Characterizing the interplay between the core gut microbiome and BSFL helps to understand the involved degradation processes and could contribute to further improving large-scale BSFL rearing.

Suitability of Black Soldier Fly Frass as Soil Amendment and Implication for Organic Waste Hygienization

“…The high moisture content of substrates and air, as well as the pleasantly warm temperature common in insect breeding, favor microbial growth. While the type of diet is known to directly influence the BSFL gut microbiome [17,44], the excrements in turn may influence the microbiome in the frass. It is likely that by agitating and mixing their surrounding substrate with feces and their inherent microorganisms, the larvae have an impact on their habitat.…”

“…The substrate used to grow insects affects the properties of the frass, since undegradable residues remain unused, while the digested fraction is modified by the gut microbiota when passing through the gastrointestinal tract [17,18]. Wang et al [19] used frass from T. molitor for subsequent rearing of BSFL to exploit leftover nutrients that T. molitor could not take up or digest.…”

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

“…While it has been recognized that both the rearing substrate nutrient composition and the microbial community (De Smet et al, 2018) composition influence rearing efficiency and reliability, previous studies typically emphasized only one aspect (Bruno et al, 2019;Klammsteiner et al, 2020) or considered both aspects but in isolation (Wynants et al, 2019;Gold et al, 2020a). We determined both substrate nutrient contents and bacterial communities and this over the rearing duration.…”

“…Researchers have previously improved rearing performance by optimizing substrate nutrient contents and ratios (Nyakeri et al, 2017;Barragán-Fonseca et al, 2018;Gold et al, 2020a), however, few studies exist regarding the manifold roles in which BSFL-associated microbiota may influence rearing performance (De Smet et al, 2018). BSFL guts, rearing substrates and residues (i.e., the mixture of frass and substrate) all have rich and diverse microbiomes (Bruno et al, 2019;Klammsteiner et al, 2020) varying due to different biotic (e.g., initial rearing substrate microbiome) and abiotic (e.g., temperature) factors among rearing systems (Wynants et al, 2019;Raimondi et al, 2020). Similar to many insects (Douglas, 2009;Engel and Moran, 2013;Lee and Brey, 2013), Dipteran larvae such as those of Drosophila melanogaster (Diptera: Drosophilidae) and Musca domestica (Diptera: Muscidae) engage in complex interactions with their gut microbiota, as these influence larval immunity (Broderick and Lemaitre, 2012) and metabolism (Shin et al, 2016), growth signaling (Storelli et al, 2011), and nutrient provision (Zurek and Nayduch, 2016).…”

Development and application of aerobic, chemically defined media forDysgonomonas

“…Sequences of the 16S rRNA gene of Dysgonomonas are prevalent in insect associations, such as honeybee [14], dipteran flies [15][16][17][18], including several Drosophila species [19][20][21], beetles [22][23][24][25][26], and several life stages of three major mosquito genera, Culex [27,28], Aedes [29,30] and Anopheles [31,32]. Dysgonomonas-derived 16S rRNA gene sequences are routinely observed associated with xylophagous cockroaches [33][34][35][36][37][38] and as ectosymbionts of nematodes living in the cockroach digestive system [39], as well as in the hindguts of phylogenetically related termites [40][41][42][43][44].…”