Identification and enzyme profiling of black soldier fly egg commensal Bacillus velezensis and its effect on food waste bioconversion

Abstract:

[Objective] A strain producing multiple enzymes was isolated from the egg surface of Hermetia illucens L. Further, the optimal growth conditions, enzyme-producing characteristics, and the effects of the strain on the food waste decomposition efficiency of Hermetia illucens L. were explored.[Methods] Enzyme-producing strains were obtained from various selective media. The optimal growth conditions, enzyme-producing characteristics, and the effects of it on the food waste treatment decomposition efficiency of Hermetia illucens L. were determined by the single-factor experiment. [Results] In this study, a Hermetia illucens L. egg-surface commensal bacterium was named as Bacillus velezensis EEAM 10B by morphological observation, biophysiological and biochemical tests, and 16S rDNA sequence analysis. The bacteria number was 3.1×10⁹ CFU/mL under the optimum growth conditions:40℃, 200 r/min, pH 7.0, 10 g/L yeast extract, 10 g/L glucose for 16 h. Approximately 95.8% single-terminal spores were formed after 24 h cultivation. Enzymes producing results are as follows:xylanase activity was the highest, followed by the protease, cellulase, pectinase, amylase, and phytase. Adding the Bacillus velezensis EEAM 10B spores to the food waste at a dosage of 1×10⁶ CFU/g significantly (P<0.05) improved the food conversion efficiency of black soldier fly larvae in both sterilized and non-sterilized food waste groups, reaching 13.4% and 13.54%, respectively, whereas the mass reduction rates did not present differences (P>0.05). Furthermore, in the sterilized food waste group, the survival rate of larvae and the prepupae weight were significantly increased to 95% and 0.1437 g per one, while the pupation rate reached 92.57% in the non-sterilized food waste group. [Conclusion] B. velezensis EEAM 10B strain can produce a variety of enzymes, and it has potential application value in the treatment of food waste with the black soldier fly.