Effects of quercetin on the growth，silk yield and gut microbiota diversity in silkworms based on high-throughput sequencing

【Objective】This study employed high-throughput sequencing to evaluate the effects of quercetin on the growth，silk yield，and gut microbiota diversity of silkworms，to elucidate quercetin’s regulatory function on the silkworm gut microecology，thereby providing a theoretical foundation for the high-quality production of functional silk. 【Method】A total of 240 silkworms of the 9 Fu×7 Xiang breed were selected and divided into 3 groups：a control group （NC group）fed with ordinary mulberry leaves，a low-dose quercetin group（LQR group）fed with mulberry leaves containing 1.25%（w/w）quercetin，and a high-dose quercetin group（HQR group）fed with mulberry leaves containing 5.00%（w/w）quercetin. Beginning at the fifth instar（day 1 of the fifth instar），the silkworms were fed continuously for 6 d. The average growth rate，survival rate and cocoon quality indexes were measured，the silkworms’gut microbiota composition was analyzed via high-throughput sequencing.【Result】After quercetin was supplemented into the silkworms’diet， their average growth rate slowed down，and survival rate decreased. The cocoon mass，cocoon shell mass，and rate of cocoon shell in the HQR group were significantly lower than those in the NC group（P<0.05，the same below）. The addition of quercetin enhanced the richness and diversity of the silkworm gut microbiota，with a significant difference in species composition observed between the HQR and NC groups. At the phylum level，the dominant bacterial phyla in all groups were Proteobacteria，Cyanobacteria，and Firmicutes. Compared with the NC group，the relative abundance of Proteobacteria in the HQR group was significantly reduced. At the genus level，the dominant bacterial genera in all groups were Achromobacter，Methylobacterium，norank_f__norank_o__Chloroplast，Sphingomonas and Acinetobacter. The relative abundance of Achromobacter in the HQR group was significantly reduced compared with the NC group. The KEGG signal pathway analysis results showed that the proportion of gut microbiota in the HQR group which annotated to global and overview maps as well as energy metabolism pathways was significantly higher than in the NC group. In contrast，the proportion that annotated to amino acid metabolism and membrane transport pathways was significantly lower than in the NC group. Similarly，COG functional annotation analysis revealed that the HQR group had a significantly lower proportion of annotations related to amino acid transport and metabolism，energy production and conversion，and inorganic ion transport and metabolism compared to the NC group. These findings aligned with the KEGG pathway analysis，suggesting that silkworms in the HQR group needed to expend more energy to sustain normal growth，while protein biosynthesis was hindered，negatively affecting both silkworm growth and silk protein synthesis.【Conclusion】The addition of quercetin to mulberry leaves alters the composition of the silkworm gut microbiota，reducing the relative abundance of Proteobacteria and Achromobacter. This shift leads to an increase in energy metabolism，but a reduction in the efficiency of amino acid metabolism，energy production and conversion，and membrane transport，ultimately impairing silkworm growth and reducing silk yield.