Abstract:  【Aim】To screen cellulose-degrading bacterial strains from the gut of Allomyrina dichotomus for constructing composite bacterial consortia and to investigate their degradation capacity for spent mushroom substrate (SMS), thereby providing theoretical and practical foundations for SMS waste management.【Methods】Composite bacterial consortia were constructed based on non-antagonistic relationships among six cellulose-degrading bacteria with high enzyme activity (Bacillus velezensis M24, Bacillus subtilis H12, H11, H4 and M33, and Bacillus siamensis M32) isolated and purified from the larval gut of A. dichotomus. The activities of four cellulases (filter paper enzyme, endoglucanase, exoglucanase and β-glucosidase) were determined, the optimal composite bacterial consortia was selected according to its enzymatic activity profile, and the culture time, inoculation amount and incubation temperature for the selected composite bacterial consortia were optimized. The structural changes in the spent mushroom substrate before and after degradation were observed through scanning electron microscope by differential weight method.【Results】The composite bacterial consortia M24∶H11 was constructed based on the enzymatic activities of filter paper enzyme, endoglucanase, exoglucanase and β-glucosidase (18.08, 69.37, 19.09 and 17.95 U/mL, respectively). The optimal culture time, inoculation amount and culture temperature of M24∶H11 were 2 d, 1% and 40 ℃, respectively. Following optimization, the activities of the four cellulases increased significantly by 1.98-2.16-fold. At 25 ℃ within 30 d, M24∶H11 showed a significantly higher SMS degradation rate (up to 38.04%) than individual strains, with the degradation rate increasing over time. The degradation by M24∶H11 effectively disrupted the SMS surface structure, increasing its contact area.【Conclusion】The larval gut-derived composite bacterial consortia M24∶H11 of A. dichotomus was constructed and optimized for enzyme production, with high efficiency in SMS degradation. This study offers novel technical insights and theoretical support for the efficient control of the edible fungi waste.

Key words:  Allomyrina dichotomus, gut microorganisms, composite bacterial consortia, cellulase, enzyme activity, spent mushroom substrate