Molecular determinants of bacterial stress responses to reactive chlorine species

由于多种适应过程和应激反应，细菌能够在各种通常有害的环境条件下生存，如热或冷、营养限制、低ph值或抗菌处理。广泛的细菌表现出的一个重要的适应和生存策略是生物膜的形成。生物膜是附着在表面并嵌入到自行产生的聚合物基质中的微生物群落。生物膜细菌已被证明具有独特的特性，包括更强的抗逆性和更高的抗菌素耐受性，导致许多技术环境中的细菌根除失败，包括饮用水和废水工业。在对不同环境应激源的筛选中，我们发现氧化应激剂和常用的活性氯类(RCS)和消毒剂次氯酸钠[NaClO，家用漂白剂]、次氯酸钙[Ca(ClO)2]和氯胺[NH2Cl]强烈刺激铜绿假单胞菌的应激反应，并在亚致死浓度下增加生物被膜的形成。这种促进生物膜形成的作用仅限于漂白剂和氯胺等活性氯物种，但不会对其他被测试的氧化剂如过氧化氢或除草剂百草枯产生影响。我们假设，漂白剂和氯胺等活性氯类物质引发的铜绿假单胞菌生物被膜刺激是一种特殊的、严格控制的应激反应和防御机制，而不足的氯化作用可能会导致抗逆性和存活率的提高。我们将以以下目标检验这些假说：1)识别和表征参与细菌应激反应和对活性氯物种的防御的关键基因；2)阐明参与RCS诱导的生物膜形成的调控网络；3)评估RCS诱导的应激反应和生物膜的生物学效应。我的研究计划的长期目标是了解细菌在恶劣环境中的应激反应和生存策略。这项工作将极大地促进我们对细菌感知和适应广泛使用的活性氯氧化剂的基本机制的基本认识，包括促进生物膜的形成，并将提出在许多重要的自然、家庭、工业或临床环境中控制细菌生长和生物膜形成的新方法。

Bacteria are able to survive under a variety of often harmful environmental conditions such as heat or cold, nutrient limitation, low ph or antimicrobial treatment due to a multitude of adaptation processes and stress responses. One important adaptation and survival strategy exhibited by a wide range of bacteria is the formation of biofilms. Biofilms are communities of microorganisms attached to a surface and embedded in a self-produced, polymeric matrix. Biofilm bacteria have been shown to possess unique characteristics including increased stress resistance and higher antimicrobial tolerance leading to failures in bacterial eradication in many technical settings including drinking and waste water industries. During a screening of different environmental stressors, we identified that the oxidative stress agents and commonly used reactive chlorine species (RCS) and disinfectants sodium hypochlorite [NaClO, household bleach], calcium hypochlorite [Ca(ClO)2] and chloramine [NH2Cl] strongly stimulated Pseudomonas aeruginosa stress responses and increased biofilm formation at sublethal concentrations. This enhanced formation of biofilms was very specific to reactive chlorine species such as bleach and chloramine, but did not occur in response to other tested oxidants likes hydrogen peroxide [H2O2] or the herbicide paraquat. We hypothesize that Pseudomonas aeruginosa biofilm stimulation triggered by reactive chlorine species such as bleach and chloramine is a specific, tightly controlled stress response and defense mechanism and that inadequate chlorination could lead to increased stress resistance and survival rates. We will test these hypotheses with the following objectives: 1) Identify and characterize key genes involved in the bacterial stress response and defense against reactive chlorine species, 2) Elucidate the regulatory networks involved in RCS-induced biofilm formation, and 3) Evaluate the biological effects of RCS-induced stress responses and biofilms. The long-term goal of my research program is to understand bacterial stress responses and survival strategies in a hostile environment. This work will greatly advance our basic knowledge on fundamental mechanisms by which bacteria sense and adapt to widely used reactive chlorine oxidants including the enhanced formation of biofilms, and will suggest new ways to control bacterial growth and biofilm formation in many important natural, domestic, industrial or clinical settings.