Controlled Diversity in Bacterial Stress Response

描述（由申请人提供）：枯草芽孢杆菌是一种重要的医学和工业土壤生长细菌，以其丰富的应激反应谱而闻名。在B使用的许多巧妙的程序中。枯草芽孢杆菌科普胁迫的能力是其摄取胞外DNA、分化成孢子、合成降解酶并变得能动的能力。长期以来，人们观察到B。枯草芽孢杆菌表现出表观遗传应激反应多样化：也就是说，在相同环境条件下的遗传等克隆细胞群中，一些细胞将开始“选择的”应激反应，而其余细胞激活替代途径。实验室条件的设计，对这种克隆多样性，在许多实验和工业应用中不希望的并发症。然而，无论是表型噪音是虚假的，存在只是因为没有强选择的统一反应;或多样化是由细胞控制，并服务于进化的目的。这一建议是基于后一种观点。我们的假设是基于越来越多的证据，即微生物的应激反应多样化可能是对不可预测环境的适应性反应，以及我们的初步建模研究。在这里，我们提出了一个有向的程序来量化概率决策在多个压力反应途径在B。subtilis，并阐明网络功能引起的切换和多样化。更具体地说，我们建议系统地测量B的分数。枯草杆菌细胞致力于孢子形成、DNA转化能力、枯草杆菌蛋白酶合成和运动性的所有可能组合，以响应一系列旨在行使控制这些过程的集成网络的每个部分的应激条件。因为我们的实验设计需要一系列的压力源，而不是单一的压力源，这些数据也将开始量化电路中的环境记忆。我们计划在平均群体水平、亚群体水平和单细胞水平上收集数据，所有这些数据都与四种应激反应的表达模式有关。该数据集通过多个模态的协调测量而变得独特，将通过与数学模型的正式比较进行分析。这项研究是第一次系统地测量，建模和解释跨多种应激反应的协调多样化，并将为未来研究微生物多样化的生理意义奠定基础。

DESCRIPTION (provided by applicant): Bacillus subtilis, a medically and industrially important soil growing bacterium, is well known for its rich stress response spectrum. Among the many ingenious programs employed by B. subtilis to cope with stress are its ability to take up extracellular DNA, differentiate into spores, synthesize degradative enzymes, and become motile. It has long been observed that B. subtilis exhibits epigenetic stress response diversification: that is, in a genetically isoclonal population of cells under identical environmental conditions, some cells will embark on the 'selected' stress response, while the remainder activate alternative pathways. Laboratory conditions are designed to militate against this clonal diversity, an undesirable complication in many experiments and industrial applications. However, either phenotypic noise is spurious, existing only because there is no strong selection for a uniform response; or diversification is controlled by the cell and serves an evolutionary purpose. This proposal is based on this latter view. We base this hypothesis on a growing body of evidence that stress response diversification in microbes can be an adaptive response to an unpredictable environment, and by our preliminary modeling studies. Here we propose a directed program to quantify the probabilistic decision-making across multiple stress response pathways in B. subtilis, and to elucidate the network features giving rise to switching and diversification. More specifically, we propose to systematically measure the fraction of B. subtilis cells committing to all possible combinations of spore formation, competence for DNA transformation, subtilisin synthesis, and motility, in response to a series of stress conditions designed to exercise each part of the integrated network controlling these processes. Because our experimental design calls for a series of stressors, rather than single stressors, these data will also begin to quantify environmental memory in the circuitry. We plan to collect data at an average population level, a subpopulation level, and a single cell level, all pertaining to the expression patterns of the four stress responses. This data set, made unique by the coordinated measurements across multiple modalities, will be analyzed through formal comparison to a mathematical model. This study is the first effort to systematically measure, model, and explain coordinated diversification across multiple stress responses, and will form the foundation for future studies on the physiological significance of diversification in microbes.