The role of bacteriocins on S. pneumoniae diversity

虽然人类最近才将化学武器加入武器库，但数百万年来，有毒物质一直是细菌和真菌的首选武器。人类利用微生物产物，如青霉素和链霉素，来治疗细菌性疾病。自从弗莱明发现青霉素以来，这些药物取得了显著的成功，改变了医疗格局，极大地改善了人类的健康。然而，微生物使用抗菌剂是相当不友好的。相反，人们认为微生物会利用这些种类繁多的毒素互相残杀，从而使生产菌株在争夺资源的斗争中占据上风。这种斗争是微生物生态学和进化的一个关键方面，对生活在土壤中的微生物和那些以病原体形式生活在人体内的微生物同样重要。最近的理论研究表明，产生不同毒素（称为细菌素）的细菌菌株之间的竞争可以导致几乎无限种类的细菌类型的进化，这些细菌类型产生不同的细菌素和细菌素抗性机制。因此，至少在理论上，一种菌株与另一种菌株之间的细菌军备竞赛与我们自己与它们之间的军备竞赛非常相似；在这两种情况下，新的药物被开发（进化），而其他药物由于耐药性的进化而失去功效。因此，这一建议的目的是了解细菌之间这种广泛的化学战的进化原因和后果。为了实现这些目标，我们将采用一种策略，将新理论的发展与一种称为实验进化的方法相结合，该方法在实验室中检查数千代细菌的进化。我们的研究系统将基于革兰氏阳性病原体肺炎链球菌产生的细菌素。肺炎链球菌仍然是全球儿童和老年人细菌性疾病的主要原因之一。这个物种的细菌素是高度多样化的，诱导它们的信号分子也是如此。信号和毒素可能有数百种不同的组合，其原因和后果尚不清楚。我们将使用下面的计划来回答这些问题。首先，我们将描述肺炎链球菌毒素的多样性和耐药性，通过在成对比赛中相互竞争的菌株。接下来，我们将通过对天然细菌菌株的相关基因进行测序来了解毒性和耐药性的遗传学。利用在这些分析中获得的信息，我们将建立理论模型来模拟细菌的多毒素群落的共同进化。我们会问这些模型在预测自然种群中毒性谱的实际多样性方面有多好。此外，我们将使用该模型来生成关于合成细菌群落进化的新预测。最后，我们将通过允许细菌菌株的混合物在实验室中进化1000代来测试这些预测。在这段进化时期之后，我们将研究竞争种群积累的表型和遗传变化。我们的结果将有几个基本和应用意义。科学家们正在努力专门组装微生物群落，以提供与健康和环境有关的服务。因此，对控制细菌病原体种群的规则进行有针对性和预测性的理解显然具有相当重要的意义。此外，细菌素越来越多地被探索作为替代抗菌剂，并已开发作为食品防腐剂。肺炎链球菌的抗生素耐药性正在增加，对替代化疗药物的需求是真实的。细菌素的成功部署依赖于对其多样性的理解以及细胞进化以抵抗它们的反应。

While mankind has only recently added chemical weapons to it's arsenal, toxic agents have been the weapons of choice for bacteria and fungi for millions of years. Humans have exploited microbial products, such as penicillin and streptomycin, to cure bacterial diseases. Since Fleming's discovery of penicillin, produced by the Penicillium mold, these drugs have worked with remarkable success, transforming the medical landscape and dramatically improving human health. The microbial use of antimicrobials, however, is considerably less friendly. Instead, microbes are believed to use these hugely diverse toxins to kill each other, thereby enabling producing strains to gain ground in the struggle for resources. This struggle is a key aspect of microbial ecology and evolution, equally important for microbes living in the soil and those living as pathogens within the human body. Recent theoretical studies have shown that competition between strains of bacteria producing different toxins, called bacteriocins, can cause the evolution of a nearly limitless variety of bacterial types that produce diverse bacteriocins and mechanisms of bacteriocin resistance. Thus, it appears, at least in theory, that the bacterial arms-race of one strain against another closely resembles our own arms-race against them; in both cases new drugs are developed (evolve) while others lose efficacy due to the evolution of resistance. The aims of this proposal are therefore to understand the evolutionary causes and consequences of this widespread chemical warfare between bacteria. To address these aims we will employ a strategy combining the development of new theory with an approach called experimental evolution, which examines the evolution of bacteria in the lab over thousands of generations. Our study system will be based upon bacteriocins produced by the gram-positive pathogen S. pneumoniae. S. pneumoniae remains one of the leading causes of bacterial diseases in children and the elderly worldwide. The bacteriocins in this species are highly diverse as are the signaling molecules that induce them. Hundreds of distinct combinations of signal and toxin can exist, the causes and consequences of which are unknown.We will use the following plan to answer these questions. First, we will characterize the diversity of S. pneumoniae toxins and resistance by competing strains against one another in pair-wise tournaments. We will next seek to understand the genetics of toxicity and resistance by sequencing the relevant genes from natural bacterial strains. Using the information gained in these analyses, we will build theoretical models to simulate the coevolution of multi-toxin communities of bacteria. We will ask how well these models predict the actual diversity of toxicity profiles in natural populations. In addition, we will use the model to generate novel predictions about evolution of synthetic bacterial communities. Finally, we will test these predictions by allowing mixtures of bacterial strains to evolve in the lab for 1,000s of generations. After this period of evolution we will study phenotypic and genetic changes that competing populations have accumulated.Our results will have several fundamental and applied implications. Scientists are working to specifically assemble microbial communites to perform heath and environment related services. It is thus clearly of considerable importance to develop a focused and predictive understanding of rules governing populations of bacterial pathogens. Furthermore, bacteriocins are increasingly being explored as alternative antimicrobials and have been developed as food preservatives. Antibiotic resistance in S. pneumoniae is increasing and the need for alternative chemotherapeutic agents is real. The successful deployment of bacteriocins relies on an understanding of their diversity and the responses cells evolve to resist them.