Life on the 'mild' side: adaptation of an extremophile archaeon to a mesophilic lifestyle

极端微生物已经进化出专门的适应性来应对恶劣的环境。在这样的条件下维持基因组完整性需要高DNA复制保真度和修复系统以防止基因组降解。然而，这些系统可能会阻碍适应嗜温条件所需的新的遗传变异的产生。该项目的目的是确定进化的过渡，和适应的限制，发生在极端嗜热古菌适应中温条件（即环境冷却和碱化）。我们将研究嗜酸热硫化叶菌的嗜中温适应，这是一种嗜热嗜酸古菌，在75-80摄氏度和pH 2-3下生长最佳。首先，我们将讨论S。嗜酸热菌在中温条件下是突变受限的。然后，我们将使用实验室实验进化来逐渐适应S。研究人员使用基因组测序技术来鉴定关键的适应性突变。最后，我们将评估是否适应嗜温条件之前，或与突变率的增加。我们假设，进化的“增强”突变将涉及一个或多个高度专业化的DNA修复和复制保真度系统的功能丧失或功能降低的变化。酸热菌。这项工作将首次确定环境特异性适应和支持嗜温适应的进化机制。这将揭示嗜极和嗜温生活方式之间的转变，正如在全球和微观尺度上不断变化的环境条件下地球生命进化史的早期可能发生的那样。

Extremophilic organisms have evolved specialised adaptations for coping with harsh environments. Maintaining genomic integrity under such conditions requires high DNA replication fidelity and repair systems to prevent genome degradation. However, these systems may hinder the generation of novel genetic variation required to adapt to mesophilic conditions. The Aim of this project is to identify evolutionary transitions, and constraints on adaptation, that occur during adaptation of an extremophile archaeon to mesophilic conditions (i.e. environmental cooling and alkalinization). We will characterise mesophilic adaptation in Sulfolobus acidocaldarius, a thermoacidophilic archaeon with optimal growth at 75-80 degrees Celsius and pH 2-3. We will first assess whether S. acidocaldarius is mutation limited under mesophilic conditions. We will then use laboratory experimental evolution to gradually adapt S. acidocaldarius to decreased temperature and increased pH, and use genomic sequencing to identify key adaptive mutations. Finally, we will assess whether adapting to mesophilic conditions was preceded by, or associated with, an increase in mutation rate. We hypothesise that evolutionary 'potentiating' mutations will involve loss-of-function or function-reducing variation in one or more of the highly-specialised DNA repair and replication fidelity systems possessed by S. acidocaldarius. This work will determine, for the first time, both the environment-specific adaptations and the evolutionary mechanisms underpinning mesophilic adaptation. This will shed light on transitions between extremophile and mesophile lifestyles, as may have occurred early in the evolutionary history of life on Earth under changing environmental conditions, on both global and microscopic scales.