Regulation of phenotypic switching and heterogeneity in Photorhabdus luminescens cell populations

发光杆菌细胞群表型转换和异质性的调节

• 批准号: 217713783
• 负责人: Professor Dr. Ralf Heermann
• 金额: --
• 依托单位: Institut für Molekulare Physiologie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/217713783?language=en
• 关键词: Regulation; phenotypic; switching; heterogeneity; Photorhabdus

Photorhabdus luminescens is an insect pathogenic bacterium that lives in close symbiosis with specific soil nematodes. The bacteria have a complex life cycle consisting of a symbiotic stage colonizing the intestinal tract of the nematodes, and a pathogenic stage outside of the nematodes within insect larvae. P. luminescens exist in two phenotypically different forms, designated as primary and secondary variants that are genetically homogeneous but differ in various morphological and physiological traits. During prolonged growth, secondary cells arise spontaneously with the result that 20-50% of the cells have undergone the transition after 28 days. This correlates with the time point when nematodes and bacteria have been re-associated and emerge from the insect cadaver. The cells that have undergone phenotypic switching are disabled in re-association and symbiosis with the nematodes. The reason for phenotypic heterogeneity of P. luminescens cell populations is rarely understood. It is assumed that secondary cells are better adapted for a life in the soil, so that splitting of the population is assumed to be a bet-hedging strategy that ensures survival of the population under any condition. However, P. luminescens cells have never been isolated from the soil, probably because they exist as metabolically inactive persister cells. The signals that induce reverse switching from the secondary to the primary variant or that can awake persister cells are unknown so far. It emerged from the previous funding period that secondary cells secrete a signal that induces the switching process in primary cells. Furthermore, primary cells emerged to inhibit growth of secondary cells revealing a simple sociobiological relation between both phenotypic variants. Identification of the chemical nature of these signals as well as the fate of the secondary cells are central questions that will be addressed in the current funding period. Furthermore, the molecular mechanism of phenotypic switching regulation will be investigated. The LysR-type regulator HexA has been identified as global regulator of the switching process. It emerged from the previous funding period that HexA is a versatile regulator that can directly or indirectly influence phenotypic heterogeneity at the transcriptional as well as the post-transcriptional level, probably via small regulatory RNAs. Identification of these small RNAs as well as the signal that is sensed by HexA to activate the switching process in single cells are further central questions that will be addressed in the current funding period. Mathematical modeling of phenotypic switching of P. luminescens will be used to contribute to the understanding of general regulation mechanisms of phenotypic heterogeneity in bacteria.

发光光habdus luminescens是一种与特定土壤线虫密切共生的昆虫致病菌。这种细菌有一个复杂的生命周期，包括寄生在线虫肠道内的共生阶段和寄生在线虫外昆虫幼虫体内的致病阶段。光棘有两种不同的表型形式，分别为初级变异和次级变异，它们在遗传上是相同的，但在各种形态和生理性状上存在差异。在长时间的生长过程中，可自发产生次生细胞，28天后约有20-50%的细胞发生了转变。这与线虫和细菌重新联系并从昆虫尸体中出现的时间点有关。经历表型转换的细胞在与线虫的重新结合和共生中被禁用。发光假单胞细胞群体表型异质性的原因尚不清楚。人们认为次生细胞更适应土壤中的生活，因此种群的分裂被认为是一种两面下注的策略，可以确保种群在任何条件下都能生存。然而，光藻细胞从未从土壤中分离出来，可能是因为它们以代谢不活跃的持久性细胞存在。诱导从继发性变异体向原发性变异体反向转换或唤醒持久性细胞的信号目前尚不清楚。从之前的资助期可以看出，次生细胞分泌一种信号，诱导原代细胞的转换过程。此外，原代细胞抑制次生细胞的生长，揭示了两种表型变异之间的简单社会生物学关系。识别这些信号的化学性质以及次生细胞的命运是当前资助期将解决的核心问题。此外，还将研究表型开关调控的分子机制。lysr型调节器HexA已被确定为开关过程的全局调节器。从之前的资助期可以看出，HexA是一种多功能调节剂，可以直接或间接地影响转录和转录后水平的表型异质性，可能是通过小的调控rna。这些小rna的识别以及HexA感知的激活单细胞转换过程的信号是当前资助期将解决的进一步核心问题。发光假单胞菌表型转换的数学模型将有助于理解细菌表型异质性的一般调节机制。