Pang Ting, Wang Xindan, Lim Hoong Chuin, Bernhardt Thomas G, Rudner David Z
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA, United States of America.
PLoS Genet. 2017 Jul 19;13(7):e1006908. doi: 10.1371/journal.pgen.1006908. eCollection 2017 Jul.
Successive division events in the spherically shaped bacterium Staphylococcus aureus are oriented in three alternating perpendicular planes. The mechanisms that underlie this relatively unique pattern of division and coordinate it with chromosome segregation remain largely unknown. Thus far, the only known spatial regulator of division in this organism is the nucleoid occlusion protein Noc that inhibits assembly of the cytokinetic ring over the chromosome. However, Noc is not essential in S. aureus, indicating that additional regulators are likely to exist. To search for these factors, we screened for mutants that are synthetic lethal with Noc inactivation. Our characterization of these mutants led to the discovery that S. aureus Noc also controls the initiation of DNA replication. We show that cells lacking Noc over-initiate and mutations in the initiator gene dnaA suppress this defect. Importantly, these dnaA mutations also partially suppress the division problems associated with Δnoc. Reciprocally, we show that over-expression of DnaA enhances the over-initiation and cell division phenotypes of the Δnoc mutant. Thus, a single factor both blocks cell division over chromosomes and helps to ensure that new rounds of DNA replication are not initiated prematurely. This degree of economy in coordinating key cell biological processes has not been observed in rod-shaped bacteria and may reflect the challenges posed by the reduced cell volume and complicated division pattern of this spherical pathogen.
球形细菌金黄色葡萄球菌的连续分裂事件在三个交替的垂直平面上定向。这种相对独特的分裂模式背后的机制以及将其与染色体分离协调起来的机制在很大程度上仍然未知。到目前为止，在这种生物体中唯一已知的分裂空间调节因子是类核阻塞蛋白Noc，它抑制细胞分裂环在染色体上的组装。然而，Noc在金黄色葡萄球菌中并非必需，这表明可能存在其他调节因子。为了寻找这些因素，我们筛选了与Noc失活具有合成致死性的突变体。我们对这些突变体的表征导致发现金黄色葡萄球菌Noc还控制DNA复制的起始。我们表明，缺乏Noc的细胞过度起始，并且起始基因dnaA中的突变抑制了这种缺陷。重要的是，这些dnaA突变也部分抑制了与Δnoc相关的分裂问题。相反，我们表明DnaA的过表达增强了Δnoc突变体的过度起始和细胞分裂表型。因此，单一因素既阻止染色体上的细胞分裂，又有助于确保不会过早启动新一轮的DNA复制。在杆状细菌中尚未观察到这种协调关键细胞生物学过程的经济程度，这可能反映了这种球形病原体细胞体积减小和复杂分裂模式所带来的挑战。
