D'Elia Michael A, Pereira Mark P, Chung Yu Seon, Zhao Wenjun, Chau Andrew, Kenney Teresa J, Sulavik Mark C, Black Todd A, Brown Eric D
Department of Biochemistry and Biomedical Sciences, Health Science Centre 4H32, 1200 Main St., W. Hamilton, ON L8N 3Z5, Canada.
J Bacteriol. 2006 Jun;188(12):4183-9. doi: 10.1128/JB.00197-06.
An extensive study of teichoic acid biosynthesis in the model organism Bacillus subtilis has established teichoic acid polymers as essential components of the gram-positive cell wall. However, similar studies pertaining to therapeutically relevant organisms, such as Staphylococcus aureus, are scarce. In this study we have carried out a meticulous examination of the dispensability of teichoic acid biosynthetic enzymes in S. aureus. By use of an allelic replacement methodology, we examined all facets of teichoic acid assembly, including intracellular polymer production and export. Using this approach we confirmed that the first-acting enzyme (TarO) was dispensable for growth, in contrast to dispensability studies in B. subtilis. Upon further characterization, we demonstrated that later-acting gene products (TarB, TarD, TarF, TarIJ, and TarH) responsible for polymer formation and export were essential for viability. We resolved this paradox by demonstrating that all of the apparently indispensable genes became dispensable in a tarO null genetic background. This work suggests a lethal gain-of-function mechanism where lesions beyond the initial step in wall teichoic acid biosynthesis render S. aureus nonviable. This discovery poses questions regarding the conventional understanding of essential gene sets, garnered through single-gene knockout experiments in bacteria and higher organisms, and points to a novel drug development strategy targeting late steps in teichoic acid synthesis for the infectious pathogen S. aureus.
在模式生物枯草芽孢杆菌中对磷壁酸生物合成进行的广泛研究已确定磷壁酸聚合物是革兰氏阳性细胞壁的重要组成部分。然而，针对与治疗相关的生物体（如金黄色葡萄球菌）的类似研究却很少。在本研究中，我们对金黄色葡萄球菌中磷壁酸生物合成酶的必要性进行了细致研究。通过使用等位基因替换方法，我们研究了磷壁酸组装的各个方面，包括细胞内聚合物的产生和输出。使用这种方法，我们证实了与枯草芽孢杆菌中的必要性研究相反，起第一步作用的酶（TarO）对于生长并非必需。经过进一步表征，我们证明了负责聚合物形成和输出的后续作用基因产物（TarB、TarD、TarF、TarIJ和TarH）对于生存能力至关重要。我们通过证明所有明显不可或缺的基因在tarO基因缺失的遗传背景下变得不再必要，解决了这一矛盾。这项工作提示了一种致死性功能获得机制，即细胞壁磷壁酸生物合成初始步骤之外的损伤会导致金黄色葡萄球菌无法存活。这一发现对通过细菌和高等生物中的单基因敲除实验所获得的关于必需基因集的传统认识提出了疑问，并指出了一种针对感染性病原体金黄色葡萄球菌的、靶向磷壁酸合成后期步骤的新型药物开发策略。
