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

Moritz Gold,Jibin Zhang,Fabienne Von Allmen,Alexander Mathys,Christian Zurbrügg

doi:10.3389/fmicb.2020.582867

Abstract

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

Highlights

Significant economic, environmental, and social impacts are associated with the avoidable disposal of foods worldwide (Gustavsson et al, 2011; Papargyropoulou et al, 2014; Chen et al, 2020)
This substrate was fed to BSFL in parallel to the non-sterile food wastes to assess the influence of the loss of the initial substrate microbiota on rearing performance and bacterial dynamics
In rearing with sterile canteen waste, larval weight, bioconversion rate, larval protein levels, and waste reduction were reduced by 18.7 mg dry mass (DM), 7.3% DM, 1.3 g protein/replicate, and 26.8% DM, respectively

Summary

Introduction

Significant economic, environmental, and social impacts are associated with the avoidable disposal of foods worldwide (Gustavsson et al, 2011; Papargyropoulou et al, 2014; Chen et al, 2020). The larval biomass is rich in proteins and lipids, and serves as a raw material for various applications within the food system, such as proteins and lipids in feeds for pets (Bosch et al, 2014) and livestock (e.g., fish, poultry, swine) (Barragán-Fonseca et al, 2017; Wang and Shelomi, 2017), and processing of the larval exoskeleton into chitosan (Hahn et al, 2019) To this recycling of waste nutrients, according to circular economy principles (Cappellozza et al, 2019), waste treatment by BSFL (Ermolaev et al, 2019; Mertenat et al, 2019; Pang et al, 2020) and animal feed products (Smetana et al, 2016, 2019) with BSFL can have lower environmental impact than the status quo (i.e., composting and commercial feed ingredients such as fish meal)

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