Growth and Colonization of the Intestine by E. coli

描述(申请人提供)：大肠杆菌是哺乳动物胃肠道中的主要兼性厌氧菌。然而，大肠杆菌如何定植其哺乳动物宿主的本质尚不清楚。根据营养生态位假说，肠道中的众多生态位是由营养可获得性定义的，物种通过竞争一种或几种有限的营养而共存。这一假说表明，共生大肠杆菌菌株可能是抵御肠道大肠杆菌病原体的第一道防线，但它还没有在这方面进行测试。在这个竞争性的更新应用中，我们建议通过检验粘液来源的营养物质提供竞争的大肠杆菌共生和致病菌株所占据的营养生态位的假设来扩展我们对肠道定植的营养基础的研究。第一个具体目标将检验这样一个假设，即不同的大肠杆菌共生和致病菌株优先使用不同的营养物质来定植小鼠的肠道。进展报告中描述的工作表明，不同的大肠杆菌菌株使用不同的营养物质进行定植。至于代表大肠杆菌四个系统发育组别的菌株，定植起始和维持阶段的特定营养需求将通过为目前获得资助的项目制定的策略来确定，即在模仿小鼠肠道的条件下在DNA阵列上诱导的基因将被敲除，并与野生型亲本竞争测试突变体，以确定它们相对适合定植的条件。第二个具体目标将检验这样一种假设，即优先利用不同的营养和/或转换为替代营养的能力是代表四个系统发育组中每一个组的大肠杆菌菌株共同定植的基础。还将检验推论，即对相同营养的直接竞争会导致其中一种菌株的定植适合性降低。这些研究可能有助于解释人类对大肠杆菌病原体感染的不同敏感性。

DESCRIPTION (provided by applicant): Escherichia coli is the predominant facultative anaerobe in the gastrointestinal tracts of mammals. Yet the essence of how E. coli colonizes its mammalian hosts is not understood. According to the nutrient-niche hypothesis, the numerous ecological niches in the intestine are defined by nutrient availability and species coexist by competing for one or a few limiting nutrients. This hypothesis suggests that commensal E. coli strains might act as a first line of defense against enteric E. coli pathogens, but it has not been tested in that light. In this competing renewal application, we propose to extend our investigation of the nutritional basis for intestinal colonization by testing the hypothesis that mucus-derived nutrients provide nutritional niches occupied by competing E. coli commensal and pathogenic strains. The first specific aim will test the hypothesis that different E. coli commensal and pathogenic strains preferentially use different nutrients for colonization of the mouse intestine. Work described in the progress report suggests that different E. coli strains use different nutrients for colonization. For strains representing the four phylogenetic groups of E. coli, the specific nutrient requirements during the initiation and maintenance stages of colonization will be determined by using strategies developed for the currently funded project, i.e., genes induced on DNA arrays under conditions designed to mimic the mouse intestine will be knocked out and the mutants tested in competition with their wildtype parent to determine their relative fitness for colonization. The second specific aim will test the hypothesis that preferential utilization of different nutrients and/or the ability to switch to alternative nutrition is the basis for co-colonization of E. coli strains representing each of the four phylogenetic groups. The corollary hypothesis will also be tested, that direct competition for the same nutrient leads to decreased fitness for colonization of one of the strains. These studies may help explain differences in human susceptibility to infection by E. coli pathogens.