Martín-Rodríguez Alberto J, Rhen Mikael, Melican Keira, Richter-Dahlfors Agneta
Department of Neuroscience, Swedish Medical Nanoscience Center, Karolinska Institutet, Solna, Sweden.
Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Solna, Sweden.
Front Microbiol. 2020 Jan 31;11:26. doi: 10.3389/fmicb.2020.00026. eCollection 2020.
To successfully colonize a variety of environments, bacteria can coordinate complex collective behaviors such as biofilm formation. To thrive in oxygen limited niches, bacteria's versatile physiology enables the utilization of alternative electron acceptors. Nitrate, the second most favorable electron acceptor after oxygen, plays a prominent role in the physiology of uropathogenic (UPEC) and is abundantly found in urine. Here we analyzed the role of extracellular nitrate in the pathogenesis of the UPEC strain CFT073 with an initial focus on biofilm formation. Colony morphotyping in combination with extensive mutational, transcriptional, and protein expression analyses of CFT073 wild-type and mutants deficient in one or several nitrate reductases revealed an association between nitrate reduction and the biosynthesis of biofilm extracellular matrix components. We identified a role for the nitrate response regulator NarL in modulating expression of the biofilm master regulator CsgD. To analyze the role of nitrate reduction during infection , we tested wild-type CFT073 and a nitrate reductase null mutant in an ascending urinary tract infection (UTI) model. Individually, each strain colonized extensively, suggesting that nitrate reduction is expendable during UTI. However, during competitive co-infection, the strain incapable of nitrate reduction was strongly outcompeted. This suggests that nitrate reduction can be considered a non-essential but advantageous fitness factor for UPEC pathogenesis. This implies that UPEC rapidly adapts their metabolic needs to the microenvironment of infected tissue. Collectively, this work demonstrates a unique association between nitrate respiration, biofilm formation, and UPEC pathogenicity, highlighting how the use of alternative electron acceptors enables bacterial pathogens to adapt to challenging infectious microenvironments.
为了成功定殖于各种环境中，细菌能够协调复杂的集体行为，如生物膜形成。为了在氧气有限的生态位中生存，细菌多样的生理机能使其能够利用替代电子受体。硝酸盐是仅次于氧气的第二大有利电子受体，在尿路致病性大肠杆菌（UPEC）的生理过程中发挥着重要作用，且在尿液中大量存在。在此，我们分析了细胞外硝酸盐在UPEC菌株CFT073发病机制中的作用，最初聚焦于生物膜形成。通过对CFT073野生型以及一种或几种硝酸盐还原酶缺陷型突变体进行菌落形态分型，并结合广泛的突变、转录和蛋白质表达分析，揭示了硝酸盐还原与生物膜细胞外基质成分生物合成之间的关联。我们确定了硝酸盐响应调节因子NarL在调节生物膜主调节因子CsgD表达中的作用。为了分析感染过程中硝酸盐还原的作用，我们在上行性尿路感染（UTI）模型中测试了野生型CFT073和硝酸盐还原酶缺失突变体。单独来看，每种菌株都能广泛定殖，这表明在UTI期间硝酸盐还原并非必需。然而，在竞争性共感染期间，无法进行硝酸盐还原的菌株被强烈淘汰。这表明硝酸盐还原可被视为UPEC发病机制中的一个非必需但有利的适应性因素。这意味着UPEC能迅速使其代谢需求适应感染组织的微环境。总体而言，这项工作证明了硝酸盐呼吸、生物膜形成与UPEC致病性之间的独特关联，突出了利用替代电子受体如何使细菌病原体适应具有挑战性的感染微环境。
