The importance of non-genotypic diversity for the fitness of microbial populations

为了在自然环境中生存，微生物必须能够科普环境变化和干扰引起的压力。环境压力的来源既包括气候波动和偶尔接触有害元素所产生的自然环境压力，也包括人类活动释放潜在有毒污染物所产生的污染。人们普遍认为，帮助物种在环境压力下生存的关键因素之一是种群内存在“遗传变异”，这是由同一物种的个体生物体之间的DNA差异引起的。这种变异意味着个体都将具有略微不同的特征，使得一些种群可能更好地适应压力条件，并允许物种生存。因此，DNA差异引起的遗传变异显然非常重要。然而，过去几年的科学突破表明，可能还有一个以前被忽视的因素对环境压力的生存很重要。对单细胞微生物的研究表明，尽管具有相同的DNA组成（即遗传上均匀），但群体中的单个细胞在环境压力下的生存能力方面具有明显不同的特征。目前正在调查其特征发生这种变化的原因，并已获得一些见解。这是一个令人兴奋的发现，因为它表明这种新的变异来源，称为“非基因型异质性”，可能是微生物在自然界中生存和克服环境压力的主要因素。然而，迄今为止，所有关于这一主题的研究都只在实验室生物中进行，因此非基因型异质性对自然界生物生存的重要性仍未得到证实。我们建议的目的是确定这种新发现的“非基因型异质性”是否在野外具有重要意义。我们计划研究一些常见的单细胞酵母，这些酵母可以很容易地从野外收集并在实验室中生长。我们有以下三个具体目标。(1)确定从野生环境中获得的酵母菌是否显示出先前实验室研究中观察到的非基因型异质性证据。为了帮助我们实现这一目标，我们开发了新的实验室测试来检测非基因型异质性。(2)确定非基因型异质性增加的酵母菌是否比变异水平低的酵母菌更有可能在环境压力下生存。(3)确定与来自低应力地区的酵母相比，在应力自然环境中发现的酵母是否表现出非基因型异质性水平增加。特别是，我们计划调查暴露于一些常见的人为污染物的城市和工业场所的酵母菌的特性。拟议项目的结果预计将提供重大的新见解的非基因型异质性在环境变化期间物种的生存可能的重要性。这将大大有助于我们了解微生物如何在自然环境中生存，以及它们如何对人类通过污染造成的有害变化作出反应。

In order to survive in the natural environment, microorganisms must be able to cope with stresses arising from environmental change and perturbation. Sources of environmental stress include both natural environmental pressures stemming from climate fluctuations and occasional exposure to harmful elements, and also pollution arising from human activities with the release of potentially-toxic contaminants. It is generally accepted that one of the key factors that helps species to survive environmental stresses is the presence of 'genetic variation' within populations, arising from differences in the DNA found among individual organisms of the same species. This variation means that individuals will all have slightly different characteristics, making it likely that some of the population will be better adapted to withstand the stressful conditions and allow the species to survive. Therefore, genetic variation due to DNA differences is clearly very important. However, scientific breakthroughs over the past few years have indicated that there may be an additional, previously overlooked, factor that is important for the survival of environmental stresses. Studies with single-cell microorganisms have shown that individual cells within a population have markedly different characteristics in their abilities to survive environmental stresses, despite having the same DNA composition (i.e. being genetically-uniform). The reasons for this variation in their characteristics are currently being investigated, with some insights already gained. This is an exciting discovery as it suggests that this new source of variation, known as 'non-genotypic heterogeneity', may be a major factor allowing microorganisms to survive and overcome environmental stress in nature. However, all of the research into this topic has so far been performed only in laboratory organisms, so the importance of non-genotypic heterogeneity for survival of organisms in nature remains unproven. The aim of our proposal is to determine whether this newly discovered 'non-genotypic heterogeneity' is in fact of importance in the wild. We plan to study some common single-cell yeasts that can be easily collected from the wild and grown in the laboratory. We have three particular objectives, as follows. (1) To determine whether yeasts obtained from the wild show evidence of non-genotypic heterogeneity as seen in previous laboratory studies. To help us achieve this we have developed novel laboratory tests to detect non-genotypic heterogeneity. (2) To determine whether yeasts that have increased non-genotypic heterogeneity are more likely to survive environmental stress than those with low levels of variation. (3) To determine whether yeasts found in stressed natural environments exhibit increased levels of non-genotypic heterogeneity compared to those from areas with low stress. In particular, we plan to investigate the characteristics of yeasts from urban and industrial sites exposed to some common man-made pollutants. The results of the proposed project are anticipated to provide major new insights into the possible importance of non-genotypic heterogeneity for the survival of species during environmental change. This will help greatly in our understanding of how microorganisms survive in the natural environment, and how they may react to harmful changes caused by mankind through pollution.