黑胸败血芽孢杆菌（Bacillus bombyseptieus，Bb）是一种典型的革兰氏阳性细菌，是家蚕生长过程中通过自然感染引起病变的主要病原之一。2009年12月1日，PLoS ONE发表了西南大学和四川农科院的研究成果，报道了鳞翅目模式昆虫家蚕对病原细菌黑胸败血芽孢杆菌侵染的分子应答特征。

研究人员在基因组水平上分析了家蚕在感染Bb前后的基因表达变化。结果显示，在Bb感染后24小时，2436个基因（占家蚕全基因组14632个基因的17%）的表达发生了至少2倍的上调或下调变化，其中1403个基因在多种幼虫组织，特别是在中肠中表达。这些表达发生变化的基因主要分为酶催化活性、结合与转运、生物学过程调节等14类，参与了遗传信息加工和转录、糖代谢、氨基酸和氮代谢、核苷酸代谢、辅因子和维生素代谢以及体内异物的生物降解和代谢等6类基础代谢途径。这表明即使只有一种病原侵染，也会引起寄主昆虫全基因组水平上的广泛应答。

有趣的是，和苏云金芽孢杆菌（Bt）相似，Bb也能够诱导蚕对毒素相关的应答反应，比如，编码中肠围食膜隔膜蛋白氨基肽酶N受体和钠/钙调蛋白的基因就被诱导表达。不仅如此，本研究还首次发现Bb能诱导激素合成和代谢途径相关基因的上调表达，可能与Bb在蚕体内的繁殖相关。另外，Bb也能够触发家蚕的免疫应答，包括细胞免疫、丝氨酸蛋白酶黑色素级联反应和体液免疫；特别重要的是，Bb能通过Toll途径诱导蚕产生系统性免疫应答，导致大量抗菌肽基因（如Attacin、Lebocin、Enbocin、Gloverin和Moricin）在Bb感染后24小时上调表达。该研究首次在基因组水平上揭示了病原微生物侵染对鳞翅目昆虫（蚕）生理代谢及免疫反应的全面影响，为我们深入理解病原和寄主昆虫之间的相互关系，以及开发提高宿主昆虫防病抗病能力的新举措提供了重要线索。

该研究是在西南大学家蚕基因组研究团队夏庆友教授的指导下，由博士研究生黄璐琳等完成，得到了国家“973”计划和长江学者创新团队项目的资助。

原始出处：

PLoS ONE 4(12): e8098. doi:10.1371/journal.pone.0008098

A Genome-Wide Survey for Host Response of Silkworm, Bombyx mori during Pathogen Bacillus bombyseptieus Infection

Lulin Huang1,3, Tingcai Cheng2, Pingzhen Xu1, Daojun Cheng1, Ting Fang1, Qingyou Xia1,2*

1 Institute of Sericulture and Systems Biology, Southwest University, Chongqing, China, 2 Institute of Agronomy and Life Science, Chongqing University, Chongqing, China, 3 Institute of Economic Crops Breeding and Cultivation, Sichuan Academy of Agricultural Sciences, Chengdu, China

Host-pathogen interactions are complex relationships, and a central challenge is to reveal the interactions between pathogens and their hosts. Bacillus bombysepticus (Bb) which can produces spores and parasporal crystals was firstly separated from the corpses of the infected silkworms (Bombyx mori). Bb naturally infects the silkworm can cause an acute fuliginosa septicaemia and kill the silkworm larvae generally within one day in the hot and humid season. Bb pathogen of the silkworm can be used for investigating the host responses after the infection. Gene expression profiling during four time-points of silkworm whole larvae after Bb infection was performed to gain insight into the mechanism of Bb-associated host whole body effect. Genome-wide survey of the host genes demonstrated many genes and pathways modulated after the infection. GO analysis of the induced genes indicated that their functions could be divided into 14 categories. KEGG pathway analysis identified that six types of basal metabolic pathway were regulated, including genetic information processing and transcription, carbohydrate metabolism, amino acid and nitrogen metabolism, nucleotide metabolism, metabolism of cofactors and vitamins, and xenobiotic biodegradation and metabolism. Similar to Bacillus thuringiensis (Bt), Bb can also induce a silkworm poisoning-related response. In this process, genes encoding midgut peritrophic membrane proteins, aminopeptidase N receptors and sodium/calcium exchange protein showed modulation. For the first time, we found that Bb induced a lot of genes involved in juvenile hormone synthesis and metabolism pathway upregulated. Bb also triggered the host immune responses, including cellular immune response and serine protease cascade melanization response. Real time PCR analysis showed that Bb can induce the silkworm systemic immune response, mainly by the Toll pathway. Anti-microorganism peptides (AMPs), including of Attacin, Lebocin, Enbocin, Gloverin and Moricin families, were upregulated at 24 hours post the infection.