GENETIC AND BIOCHEMICAL ANALYSES OF ADAPTIVE MUTATIONS I

在过去的5年里，对大肠杆菌的遗传和生化研究揭示了被称为适应性突变事件的新的突变，这些突变发生的频率很高(即通常比对数生长期间发生的突变高3到5个对数)，只在特殊的适应条件下发生，并且在细菌生长的静止阶段发生。我们最近对志贺氏菌的研究表明，志贺氏菌在许多寡糖利用途径以及其他代谢和毒力基因区域也经历了适应性突变。该项目旨在表征志贺氏菌在不同代谢和毒力基因座上的遗传和生化适应性突变事件的频率和化学性质。将对所涉及的基因座进行DNA测序，以检查突变事件的确切性质，重点是了解在静止期细胞中刺激这些高频(例如10-3)突变事件的机制。将对其他相关的肠道细菌进行类似的研究，以确定适应性突变是否是通过改变的生化途径或细菌调节其毒力的方法错误识别病原体的原因。

Genetic and biochemical studies of Escherichia coli over the past 5 years have revealed novel mutations, termed adaptive mutational events, that occur at high frequency(i.e. generally 3 to 5 logs higher than mutations occurring during logarithmic growth), only under special adaptive conditions, and in the stationary phase of bacterial growth. Our recent studies of Shigella indicate that this organism also undergoes adaptive mutations in a large variety of oligosaccharide utilization pathways and in other metabolic and virulence gene regions. This project is aimed at characterizing genetically and biochemically adaptive mutational events in Shigella at various metabolic and virulence gene loci for frequency and chemical nature. Involved loci will be DNA sequenced to examine the precise nature of the mutational event, with an emphasis on understanding the mechanisms involved in stimulating these high frequency ( e.g. 10-3) mutational events in stationary phase cells. Similar studies of other related enteric bacteria will be conducted to determine if adaptive mutations are a cause of misidentification of pathogens, via altered biochemical pathways, or a method by which bacteria modulate their virulence.