Beneficial efficacy and mode of action of probiotic Bacillus subtilis SWL−19 on the silkworm (Bombyx mori L.)

The safety and efficacy of probiotic Bacillus subtilis to raising animals in the livestock and poultry have been widely evaluated. Silkworm (Bombyx mori L.) is a well-known economic rearing insect, and its artificial diet rearing is gaining interest. However, the effects of probiotic B. subtilis as feed additive on silkworms fed with an artificial diet remain unknown. In this study, we adopted multiple biological approaches (enzyme activity assay, quantitative PCR, transcriptome sequencing, and LC-MS) to explore the beneficial effects of B. subtilis SWL−19 on silkworm physiology. Results showed that the body weights of the silkworms significantly increased (P < 0.05) after feeding with SWL−19 strain. B. subtilis SWL−19 evidently enhanced the antioxidant property in the silkworms, and the gene expression levels of antimicrobial peptides (attacin, lysozyme, and cecropins) were affected by the SWL−19 strain. Moreover, the levels of riboflavin, nicotinamide, pyridoxine, and pyridoxal in the hemolymph of the silkworms remarkably increased after SWL−19 strain feeding. The results of transcriptomic analysis indicated that the response of intestinal tissues to B. subtilis SWL−19 focused mainly on the categories of external biotic stimulus, interspecies interaction between organisms, immune system process, and stress response. In conclusion, probiotic B. subtilis SWL−19 substantially enhanced the body weight and antioxidant property of silkworm and simultaneously regulated the intestinal immunity and promoted the metabolism of B vitamins. The present study provides a theoretical reference for the application of probiotic B. subtilis SWL−19 to improve silkworm physiology under artificial diet rearing condition.