关键词: 家蚕, 抗菌肽, 乳杆菌, RNAref转录组测序, 黏质沙雷氏菌

Abstract: 【Aim】To explore the effect of Lactobacillus on the transcription level of antimicrobial peptide genes in Bombyx mori. 【Methods】After spraying the suspension (2×10⁸ CFU/mL) of Lactobacillus plantarum FLPL028, L. rhamnosus FLRH956 and L. reuteri FLRE589 to the mulberry leaves (20 μL/cm²) to feed the 1st instar larvae of B. mori, the RNAref transcriptome sequencing of the 5th instar larvae was performed and the mortality rate before cocooning of B. mori after feeding the 5th instar larvae with the mulberry leaves sprayed with the suspension (2×10⁶ CFU/mL, 20 μL/cm²) of Serratia marcescens was calculated. The numbers of viable bacteria of S. marcescens were counted at 4 h after incubation with L. plantarum FLPL028, L. rhamnosus FLRH956 and L. reuteri FLRE589, respectively. The expression levels of immune-related genes including LOC101742127, glv1,glv2, CecA, LOC101739681, CecD, Attacin1, Leb3 and Lzm (antimicrobial peptide genes), LOC692824 (lectin gene), PGRP-S1 and LOC101738493(Toll/Imd signaling pathway-related genes), and Pi3k60, MAPK and Ras2(PI3K and MAPK signaling pathway-related genes) in the 5th instar larvae of B. mori were detected by qPCR. 【Results】After the 1st instar larvae of B. mori were fed with L. plantarum FLPL028, L. rhamnosus FLRH956 and L. reuteri FLRE589, respectively, the transcription levels of most antimicrobial peptide genes, including Moricin, glv4-like and glv2, were significantly decreased in the 5th instar larvae, and that of Moricin decreased the most, as compared with those of the control group. After the 1st instar larvae of B. mori were fed with L. plantarum FLPL028, L. rhamnosus FLRH956 and L. reuteri FLRE589, respectively, the transcription levels of lectin genes such as CTL10, CTL19 and LOC101736606, and Toll/Imd signaling pathway-related genes PGRP-S2, LOC101738325 and LOC101738493 in the 5th instar larvae decreased, and those of PI3K and MAPK signaling pathway-related genes Pi3k60 and MAPK were increased by about 2.4- and 2.1-fold, respectively, as compared with those of the control group. However, the above three species of Lactobacillus had antagonistic effects on S. marcescens, and reduced the mortality rate of B. mori in the model group (only fed with S. marcescens) from 83% to less than 35%, among them L. reuteri FLRE589 had the best antagonistic effect on S. marcescens, causing only 18.1% mortality rate of the 5th instar larvae of B. mori. The basic change trends of the expression levels of LOC101742127, glv1, glv2, CecA, LOC101739681, CecD, Attacin1, Leb3, Lzm, LOC692824, LOC101738493, PGRP-S1, Pi3k60, MAPK and Ras2 were consistent with those of RNAref transcriptome sequencing results. The supernatant of the fermentation of these three species of Lactobacillus could effectively kill S. marcescens and reduce the number of viable bacteria of S. marcescens.【Conclusion】Lactobacilli inhibits the expression of antimicrobial peptide genes and Toll/Imd immune pathway-related genes in B. mori, reduces the innate immune response of B. mori, but is conducive to the harmony between Lactobacilli and B. mori. In addition, Lactobacilli can also improve the acquired immunity of B. mori by activating the PI3K and MAPK signaling pathways. This finding will help to understand the immune system of B. mori more comprehensively and provide a new strategy for the prevention and control of diseases in B. mori industry.

Key words: Bombyx mori, antimicrobial peptides; Lactobacillus, RNAref transcriptome sequencing; Serratia marcescens