Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, United States of America.
PLoS Pathog. 2010 Aug 26;6(8):e1001065. doi: 10.1371/journal.ppat.1001065.
The survival of a bacterial pathogen within a host depends upon its ability to outmaneuver the host immune response. Thus, mutant pathogens provide a useful tool for dissecting host-pathogen relationships, as the strategies the microbe has evolved to counteract immunity reveal a host's immune mechanisms. In this study, we examined the pathogen Francisella novicida and identified new bacterial virulence factors that interact with different parts of the Drosophila melanogaster innate immune system. We performed a genome-wide screen to identify F. novicida genes required for growth and survival within the fly and identified a set of 149 negatively selected mutants. Among these, we identified a class of genes including the transcription factor oxyR, and the DNA repair proteins uvrB, recB, and ruvC that help F. novicida resist oxidative stress. We determined that these bacterial genes are virulence factors that allow F. novicida to counteract the fly melanization immune response. We then performed a second in vivo screen to identify an additional subset of bacterial genes that interact specifically with the imd signaling pathway. Most of these mutants have decreased resistance to the antimicrobial peptide polymyxin B. Characterization of a mutation in the putative transglutaminase FTN_0869 produced a curious result that could not easily be explained using known Drosophila immune responses. By using an unbiased genetic screen, these studies provide a new view of the Drosophila immune response from the perspective of a pathogen. We show that two branches of the fly's immunity are important for fighting F. novicida infections in a model host: melanization and an imd-regulated immune response, and identify bacterial genes that specifically counteract these host responses. Our work suggests that there may be more to learn about the fly immune system, as not all of the phenotypes we observe can be readily explained by its interactions with known immune responses.
细菌病原体在宿主体内的存活取决于其规避宿主免疫反应的能力。因此，突变病原体为剖析宿主-病原体关系提供了有用的工具，因为微生物为对抗免疫而进化出的策略揭示了宿主的免疫机制。在这项研究中，我们研究了弗朗西斯氏菌 novicida，并鉴定了与黑腹果蝇先天免疫系统不同部分相互作用的新细菌毒力因子。我们进行了全基因组筛选，以鉴定在果蝇体内生长和存活所需的 F. novicida 基因，并确定了一组 149 个负选择突变体。在这些突变体中，我们鉴定了一类基因，包括转录因子 oxyR 和 DNA 修复蛋白 uvrB、recB 和 ruvC，它们帮助 F. novicida 抵抗氧化应激。我们确定这些细菌基因是毒力因子，使 F. novicida 能够对抗果蝇黑化免疫反应。然后，我们进行了第二次体内筛选，以鉴定与 imd 信号通路特异性相互作用的另一组细菌基因。这些突变体大多数对抗菌肽多粘菌素 B 的抗性降低。鉴定假定转谷氨酰胺酶 FTN_0869 中的突变产生了一个有趣的结果，用已知的果蝇免疫反应很难解释。通过使用无偏遗传筛选，这些研究从病原体的角度提供了对果蝇免疫反应的新观点。我们表明，果蝇免疫的两个分支对在模型宿主中对抗 F. novicida 感染很重要：黑化和 imd 调节的免疫反应，并鉴定了专门对抗这些宿主反应的细菌基因。我们的工作表明，可能还有更多关于果蝇免疫系统的知识有待了解，因为我们观察到的并非所有表型都可以通过其与已知免疫反应的相互作用来轻易解释。
