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

为了在自然环境中生存，微生物必须能够应对环境变化和扰动带来的压力。环境压力的来源既包括气候波动和偶尔暴露在有害元素中的自然环境压力，也包括人类活动释放的潜在有毒污染物造成的污染。人们普遍认为，帮助物种在环境压力下幸存下来的关键因素之一是种群内存在“遗传变异”，这种变异是由同一物种的个体生物之间发现的DNA差异引起的。这种变异意味着所有个体都将具有略有不同的特征，使得一些种群可能会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是非常重要的。然而，过去几年的科学突破表明，对于环境压力的生存，可能还有一个以前被忽视的额外因素。对单细胞微生物的研究表明，尽管具有相同的DNA组成(即基因一致)，但种群中的单个细胞在生存环境压力方面具有明显不同的特征。目前正在调查它们特征的这种差异的原因，已经获得了一些见解。这是一个令人兴奋的发现，因为它表明这种新的变异源，即所谓的“非基因异质性”，可能是允许微生物在自然界中生存和克服环境压力的主要因素。然而，到目前为止，所有关于这一主题的研究都只在实验室生物体中进行，因此非基因异质性对自然界中生物体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“非基因异质性”在野外是否真的很重要。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培养。我们有三个特别的目标，如下所示。(1)确定从野外获得的酵母菌是否表现出先前实验室研究中所看到的非基因异质性的证据。为了帮助我们实现这一点，我们开发了新的实验室测试来检测非基因异质性。(2)确定非基因异质性增加的酵母是否比变异水平较低的酵母更有可能在环境压力下生存。(3)确定在紧张的自然环境中发现的酵母与来自低压力地区的酵母相比，是否表现出更高水平的非基因异质性。特别是，我们计划调查来自城市和工业场所的酵母菌暴露在一些常见的人为污染物中的特征。预计拟议项目的结果将为环境变化期间非遗传型异质性对物种生存的可能重要性提供重要的新见解。这将极大地帮助我们了解微生物如何在自然环境中生存，以及它们如何应对人类通过污染造成的有害变化。

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.