Comparative in vivo gene expression of the closely related bacteria Photorhabdus temperata and Xenorhabdus koppenhoeferi upon infection of the same insect host, Rhizotrogus majalis.
Comparative in vivo gene expression of the closely related bacteria Photorhabdus temperata and Xenorhabdus koppenhoeferi upon infection of the same insect host, Rhizotrogus majalis.
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DOI：
10.1186/1471-2164-10-433
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发表时间：
2009-09-15
期刊：
影响因子：
4.4
通讯作者：
Grewal PS
中科院分区：
文献类型：
--
作者：
An R;Sreevatsan S;Grewal PS
Photorhabdus和Xenorhabdus是革兰氏阴性的肠杆菌，系统发育相关，分别与昆虫病原线虫Heterorhabditis和Steinernema形成共生关系。寄生在线虫感染幼体肠道内的共生细菌被线虫释放到昆虫的血淋巴中，对昆虫具有致病性。这种转换需要激活促进细菌毒力的基因。采用选择性转录序列捕获技术，研究了白蛴螬侵染后温度光habdus和koppenhoeferxenorhabdus在体内的基因表达。在感染后24 h，共有40个基因和39个基因在黄颡鱼血淋巴中表达上调。通过比较杂交实验证实了这些基因在两种细菌中特异性存在或上调，并通过实时荧光定量PCR进一步验证了随机选择基因的变化。所鉴定的基因大致可分为细胞表面结构、调控、毒力与分泌、应激反应、细胞内代谢、营养清除和未知等7个功能群。这两种细菌在应激反应类别中共享的基因比任何其他功能群都多。超过60%的鉴定基因在两种细菌中都是唯一诱导的，这表明对同一昆虫宿主的致病性分子机制存在巨大差异。在黄貂鱼中诱导编码转录激活因子的基因lysR，在黄貂鱼中诱导编码转录抑制因子的基因yijC和rseA。脂多糖合成基因lpsE在黄颡鱼中有诱导作用，在黄颡鱼中无诱导作用。除tcaC和溶血素相关基因外，其他毒力基因在两种细菌之间存在差异。参与TCA循环的基因在温热假单胞菌中被诱导，而参与乙醛酸途径的基因在柯氏假单胞菌中被诱导，这表明在同一昆虫宿主中，两种细菌的代谢存在差异。编码不同类型营养摄取系统的基因的上调进一步强调了同一昆虫宿主中两种细菌营养需求的差异。温光habdus表现出铁载体依赖性铁摄取系统编码基因的上调，而X. koppenhoferi则表现出铁载体非依赖性离子摄取系统编码基因的上调。温度光habdus诱导氨基酸获取基因，而X. koppenhoeferi上调malF基因，编码麦芽糖摄取系统。进一步的分析确定了代谢途径中所鉴定的基因产物之间可能的机制关联，为每种细菌的发病机制提供了一个相互作用的模型。本研究鉴定了一组温度假单胞菌（P. temperata）和koppenhoeferi在感染马氏绦虫（R. majalis）后诱导的基因，并强调了这两种密切相关的细菌在同一昆虫宿主中促进致病性所使用的分子特征的差异。
Photorhabdus and Xenorhabdus are Gram-negative, phylogenetically related, enterobacteria, forming mutualism with the entomopathogenic nematodes Heterorhabditis and Steinernema, respectively. The mutualistic bacteria living in the intestines of the nematode infective juveniles are pathogenic to the insect upon release by the nematodes into the insect hemolymph. Such a switch needs activation of genes that promote bacterial virulence. We studied in vivo gene expression in Photorhabdus temperata and Xenorhabdus koppenhoeferi upon infection of the white grub Rhizotrogus majalis using selective capture of transcribed sequences technique. A total of 40 genes in P. temperata and 39 in X. koppenhoeferi were found to be upregulated in R. majalis hemolymph at 24 h post infection. Genomic presence or upregulation of these genes specific in either one of the bacterium was confirmed by the assay of comparative hybridization, and the changes of randomly selected genes were further validated by quantitative real-time PCR. The identified genes could be broadly divided into seven functional groups including cell surface structure, regulation, virulence and secretion, stress response, intracellular metabolism, nutrient scavenging, and unknown. The two bacteria shared more genes in stress response category than any other functional group. More than 60% of the identified genes were uniquely induced in either bacterium suggesting vastly different molecular mechanisms of pathogenicity to the same insect host. In P. temperata lysR gene encoding transcriptional activator was induced, while genes yijC and rseA encoding transcriptional repressors were induced in X. koppenhoeferi. Lipopolysaccharide synthesis gene lpsE was induced in X. koppenhoeferi but not in P. temperata. Except tcaC and hemolysin related genes, other virulence genes were different between the two bacteria. Genes involved in TCA cycle were induced in P. temperata whereas those involved in glyoxylate pathway were induced in X. koppenhoeferi, suggesting differences in metabolism between the two bacteria in the same insect host. Upregulation of genes encoding different types of nutrient uptake systems further emphasized the differences in nutritional requirements of the two bacteria in the same insect host. Photorhabdus temperata displayed upregulation of genes encoding siderophore-dependent iron uptake system, but X. koppenhoeferi upregulated genes encoding siderophore-independent ion uptake system. Photorhabdus temperata induced genes for amino acid acquisition but X. koppenhoeferi upregulated malF gene, encoding a maltose uptake system. Further analyses identified possible mechanistic associations between the identified gene products in metabolic pathways, providing an interactive model of pathogenesis for each bacterium species. This study identifies set of genes induced in P. temperata and X. koppenhoeferi upon infection of R. majalis, and highlights differences in molecular features used by these two closely related bacteria to promote their pathogenicity in the same insect host.
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