Abstract
In the present research, bacterial diversity was studied during a 6-month feeding trial utilizing zebrafish (Danio rerio) fed Hermetia illucens reared on different substrates with an emphasis on fish gut bacterial diversity. A polyphasic approach based on viable counting, PCR-DGGE and metagenomic 16S rRNA gene amplicon target sequencing was applied. Two different H. illucens groups were reared on coffee by-products (C) or a mixture of vegetables (S). Viable counts showed a wide variability based on substrate. PCR-DGGE and Illumina sequencing allowed the major and minor bacterial taxa to be detected. Both samples of larvae and their frass reared on the S substrate showed the highest richness and evenness of bacterial communities, whereas zebrafish (ZHC) fed H. illucens reared on substrate C and zebrafish (ZHS) fed H. illucens reared on substrate S had the lowest bacterial richness and evenness. A stimulating effect of bioactive compounds from coffee by-products on the occurrence of Lactobacillaceae and Leuconostoccaceae in H. illucens reared on substrate C has been hypothesized. Zebrafish gut samples originating from the two feeding trials showed complex microbial patterns in which Actinobacteria and Alteromonadales were always detected, irrespective of the diet used. Enterobacteriaceae in fish guts were more abundant in ZHS than in ZHC, thus suggesting an influence of the bioactive compounds (chlorogenic and caffeic acids) in the substrate on Enterobacteriaceae in fish guts. ZHC showed a higher abundance of Clostridia than did ZHS, which was likely explained by stimulating activity on the bacteria in this class by the bioactive compounds contained in H. illucens reared on substrate C. An influence of the microbiota of H. illucens or insect-derived bioactive compounds on the gut microbiota of zebrafish has been suggested. The presence of bacteria consistently associated with zebrafish guts has been found irrespective of the diet, thus attesting to the likely stability of the core fish microbiota.
Highlights
The use of edible insects as food and feed could represent a suitable source of alternative protein due to their high-quality nutritional values and the environmental sustainability of their rearing [1, 2]
Enterobacteriaceae counts in samples HC and HCF were lower than that in sample C, reflecting the previously described inhibitory effect of H. illucens larvae on Enterobacteriaceae [33]
The data collected on mesophilic aerobes, bacterial spores, and LAB were consistent with those reported by Wynants et al [17] that reflected a wide variability based on the substrate, the rearing methods and the timing of larval harvest
Summary
The use of edible insects as food and feed could represent a suitable source of alternative protein due to their high-quality nutritional values and the environmental sustainability of their rearing [1, 2]. Edible insects are already reared in Asia, Africa, Oceania and South America, representing a growing source of income [3, 4]. In the European Union (EU), stakeholders have recently begun paying attention to the applications of edible insects as food or feed. In 2015, the European Food Safety Authority (EFSA) listed a few insect species with potential use as food and feed in the EU. The EFSA highlighted the need for in-depth studies to assess the safety of edible insects to achieve large-scale production [6]. Since insects can be natural reservoirs of microorganisms that can be transferred to the environment and to living animals used as food sources, their microbiological assessment must be properly conducted [7]
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