Chitinolytic Bacillus spp. enhanced chitin degradation and improved nutritional composition of black soldier fly (Hermetia illucens) for potential use in aquafeeds

The increasing demand for sustainable protein sources in aquaculture has prompted the exploration of alternative ingredients, such as black soldier fly (Hermetia illucens) prepupae (BSFp) meal, as substitutes for fishmeal. However, the high chitin content in BSFp limits its inclusion levels due to its adverse effects on protein absorption and hinders growth in aquatic organisms. This study investigates the potential of chitinolytic Bacillus spp. to enhance the nutritional value of BSFp by degrading chitin into bioavailable components. Chitin was extracted from BSFp and used as a substrate to evaluate the chitinolytic activities of five Bacillus strains (B. pasteurii, B. cereus, B. licheniformis, B. megaterium, and B. subtilis). The results demonstrated significant chitinase production across all tested Bacillus strains, with B. licheniformis and B. megaterium showing the highest activity, followed by B. cereus, particularly at 109 CFU/ml after 72 hours of incubation at 30 °C. Furthermore, chitinolytic Index (CI) showed that the Bacillus species are capable of degradation of chitin in the colloidal chitin medium. On the other hand, B. licheniformis and B. subtilis exhibited a wide range of probiotic properties, including acid and bile tolerance, antimicrobial activity, and resistance to gastric juices. In addition, their chitinolytic activity highlights their potential as dual-function additives in aquafeeds, combining both probiotic properties and chitin-degrading capabilities. In conclusion, the findings of this study highlight the potential of Bacillus strains in improving the nutritional quality of BSFp by enhancing the chitin content degradation, offering a viable approach to overcome the challenges associated with chitin in insect-based fish feed formulations.