Effects of brewery by-products on growth performance, bioconversion efficiency, nutritional profile, and microbiota and mycobiota of black soldier fly larvae.

Brewery by-products are recognised as suitable rearing substrates for Hermetia illucens, better known as black soldier fly (BSF) but information about the impact of different ratios of brewer's spent grains (BSG) and brewer's spent yeast (BSY) are still scarce. This study evaluated the effects of BSG-BSY-based diets on BSF larval growth, survival, bioconversion efficiency, nutritional profile, and microbiota and mycobiota. A total of 3 000 6-day-old BSF larvae were allotted to five dietary treatments (six replicate boxes/diet, 100 larvae/box): (i) BSY2.5 (25 g/kg of BSY+975 g/kg of BSG), (ii) BSY5 (50 g/kg of BSY+950 g/kg of BSG), (iii) BSY7.5 (75 g/kg of BSY+925 g/kg of BSG), (iv) BSY10 (100 g/kg of BSY+900 g/kg of BSG), and (v) control (Gainesville diet). Larval weight and substrate pH were recorded every 4 days. At the end of the trial (5% of prepupae), bioconversion efficiency corrected for residue (BER), reduction rate (RR), and waste reduction index (WRI) were calculated, and the larval proximate composition, microbiota and mycobiota characterised. At 10 and 14 days of age, BSY7.5 and BSY10 larvae displayed higher weight than BSY2.5 and BSY5 (P < 0.05), with BSY10 larvae showing the highest weight among the BSG-BSY-based diets at the end of the trial (P < 0.05). The BSY7.5 and BSY10 larvae also displayed a better BER than BSY2.5 and BSY5 (P < 0.01), whereas similar RR, WRI, survival and development time, as well as pH, were, however, observed among the BSG-BSY-based diets (P > 0.05). The BSY10 larvae displayed lower ether extract content than the other BSG-BSY-based diets (P > 0.001). The use of BSG-BSY-based diets did not influence the alpha diversity of larval microbiota and mycobiota (P > 0.05), but a specific microbial signature was identified per each dietary treatment (Porphyromonadaceae [BSY5], Sphingomonas [BSY7.5], Bacillus [BSY10] and Ruminococcus and Myroides [BSG-BSY-based diets]; P < 0.05). Co-occurrence and co-exclusion analysis also showed that Saccharomyces cerevisiae and Pichia excluded and favoured, respectively, the presence of Streptomyces and Fluviicola, while Clavispora lusitaniae was associated with Myroides (P < 0.05). In conclusion, BSG-BSY-based diets are suitable for rearing HI in terms of larval performance, nutritional profile, and microbiota and mycobiota, with 7.5 and 10% of BSY inclusion levels being able to improve larval growth and bioconversion efficiency.

Wheat starch processing by-products as rearing substrate for black soldier fly: does the rearing scale matter?

Rearing scale may influence black soldier fly (BSF) larvae traits when they are fed on a single diet, but different feeding substrates have not been tested yet. This study evaluated the effects of wheat starch processing by-products-based diets on growth performance, bioconversion efficiency, and nutritional profile of BSF larvae reared in different scales. Four diets (D1 and D2 [isonitrogenous, isolipidic and isoenergetic]; D3 and D4 [displaying 1:1 and 1:2 as protein to carbohydrate ratios, respectively]) were tested at 3 rearing scales (4 replicate boxes/diet, with a constant volume [0.84 cm3]/larva and feed [0.7 g]/larva): 1) small (S; 12 × 12 cm, substrate height: 4 cm, 686 6-day-old larvae (6-DOL)/box), 2) medium (M, 32 × 21 cm, substrate height: 7 cm, 5 600 6-DOL/box), and 3) large (L, 60 × 40 cm, substrate height: 7 cm, 20 000 6-DOL/box). Larval weight was recorded at the beginning of trial and every 4 days, and growth rate (GR), specific growth rate (SGR), feed conversion ratio (FCR), survival, bioconversion efficiency corrected for residue (BER), reduction rate (RR), and waste reduction index (WRI) calculated at the end of larval growth (frass DM ≥ 55%). Substrate pH, T and height were measured at the beginning, every 4 days, and end of trial. Larval proximate composition was analysed at the end of trial. Data were analysed by generalised linear mixed model (SPSS software, P < 0.05). The D1 larvae showed higher weight, GR, SGR and WRI (along with higher substrate T) than D2 at M scale, while increased SGR and FCR - as well as decreased survival, RR and WRI - were observed in D2 larvae at S scale (P < 0.05). Larval CP and ether extract (EE) contents were influenced by M and L scales only, being higher in D2 group than in D1 (P < 0.001). Differently, decreased ash was recorded in D2 larvae when reared at S and M scales, while L scale revealed higher ash in D2 group than D1 (P < 0.001). The D3 larvae displayed greater weight, SGR, survival, RR and WRI (along with greater substrate T) than D4 at M scale, with increased survival and substrate T being also highlighted in L scale (P < 0.05). The D3 larvae also showed lower DM and EE - as well as higher CP - than D4 at all the rearing scales (P < 0.001). In conclusion, D1 and D3 led to better BSF larval growth performance, bioconversion efficiency and nutritional profile mainly at M and L scales, as a consequence of their ability to facilitate larval aggregation and, in turn, allow achieving a higher substrate T.

Determination of lipid requirements in black soldier fly through semi-purified diets.

The insect market is still far from an effective upscale and, to achieve this goal, it is necessary to know the BSF dietary requirements for the production maximization. Worldwide, given the waste variability, is not always easy to identify the optimal waste-based mixture that can allow to reach the best production, in terms of quantity and quality. Due this reason, nutritional need ranges are the basic knowledge, affordable for everyone, to increase the profitability of the insect farming. The study aims to evaluate the effects of 6 semi-purified, isonitrogenous and isoenergetic diets (SPII) with increasing lipid levels (1%, L1; 1.5%, L1.5; 2.5%, L2.5; 3.5% L3.5; 4.5%, L4.5) on BSF life history traits (6 replicates/treatment and 100 larvae/replicate). The Gainesville diet was used as environmental control. Considering the whole larval stage, 4.5% lipid level guarantees better performance when compared to content lower than 2.5%. The L4.5 10-day-old larvae yielded greater when compared to the other dietary treatments. At 14 and 18 days of age, the larvae of the groups above 2.5% performed better than L1, while the L1.5 showed intermediate results. Lipid levels below 1.5% on DM, when compared to 4.5%, resulted in a smaller prepupa and pupa size. The results obtained on the adult stage do not allow the identification of a lipid levels ideal range, as in the larval stage. In conclusion, in the whole larval stage and in prepupae/pupae phases, lipid percentage lower than (or equal to) 1% have a negative effect on growth. Other research will be needed in order to evaluate lipid levels above 4.5% on DM.

Reporter gene technology to assess activity of antimycobacterial agents in macrophages.

Reporter strains of Mycobacterium tuberculosis and Mycobacterium bovis BCG endogenously expressing firefly luciferase were used in bioluminescence assays to evaluate the activities of isoniazid and rifampin against mycobacteria sequestered in human macrophages. This methodology allowed the efficacy of antibiotics against intracellular mycobacteria to be assessed without the labor-intensive procedures and protracted incubation requirements associated with conventional CFU determinations.

Bioluminescence screening in vitro (Bio-Siv) assays for high-volume antimycobacterial drug discovery.

Bioluminescence-based assays to indicate antimicrobial susceptibility have been developed and validated for recombinant strains of Mycobacterium tuberculosis, Mycobacterium bovis BCG, Mycobacterium avium, and Mycobacterium intracellulare expressing an integrated eukaryotic luciferase gene. MICs determined with these bioluminescence assays for several antimycobacterial agents, including isoniazid, ethambutol, rifampin, amikacin, streptomycin, ciprofloxacin, and clarithromycin, compared favorably with traditional BACTEC methods and visual estimations of the inhibitory end point. Assay methodology has been optimized for the analysis of large numbers of novel compounds and is simple, inexpensive, and labor efficient. The availability of these four recombinant mycobacteria has permitted a strategy for drug discovery employing the nonpathogenic BCG strain for mass screening purposes with subsequent confirmation of activity against the pathogenic mycobacteria. Furthermore, evidence suggests that the BCG-based screen may allow the direct identification of bactericidal agents.

Differential susceptibilities of enterococcal species to elfamycin antibiotics.

The elfamycins are a class of naturally occurring antibiotics not currently used in the therapy of human disease. Enterococcus faecium and closely related species (Enterococcus durans and Enterococcus hirae) are susceptible to these antibiotics, while isolates of Enterococcus faecalis and other enterococcal species are highly resistant. Among enterococci, susceptibility or resistance to elfamycins appears to be determined by the bacterial protein synthesis elongation factor EF-Tu. Elfamycin susceptibility may be a useful adjunct for rapidly distinguishing E. faecalis and E. faecium in the clinical microbiology laboratory and/or as a supplementary test for use in determining the species of enterococci.

In vitro antimicrobial activity of a new antibiotic, MDL 62,879 (GE2270 A).

MDL 62,879 (GE2270 A) is a new peptide antibiotic that inhibits protein synthesis through an interaction with elongation factor Tu. MDL 62,879 was very active against gram-positive clinical isolates, particularly staphylococci and enterococci, for which MICs for 90% of isolates were < or = 0.13 micrograms/ml. It was equally active against isolates resistant to beta-lactams, erythromycin, gentamicin, and glycopeptides. It also had activity against Mycobacterium tuberculosis. MDL 62,879 had moderate bactericidal activity against staphylococci.