Logsdon Michelle M, Aldridge Bree B
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, MA, United States.
Department of Molecular Microbiology, Sackler School of Graduate Biomedical Sciences, Tufts University, Boston, MA, United States.
Front Microbiol. 2018 Mar 21;9:514. doi: 10.3389/fmicb.2018.00514. eCollection 2018.
Model bacteria, such as and , tightly regulate cell cycle progression to achieve consistent cell size distributions and replication dynamics. Many of the hallmark features of these model bacteria, including lateral cell wall elongation and symmetric growth and division, do not occur in mycobacteria. Instead, mycobacterial growth is characterized by asymmetric polar growth and division. This innate asymmetry creates unequal birth sizes and growth rates for daughter cells with each division, generating a phenotypically heterogeneous population. Although the asymmetric growth patterns of mycobacteria lead to a larger variation in birth size than typically seen in model bacterial populations, the cell size distribution is stable over time. Here, we review the cellular mechanisms of growth, division, and cell cycle progression in mycobacteria in the face of asymmetry and inherent heterogeneity. These processes coalesce to control cell size. Although and Bacillus Calmette-Guérin (BCG) utilize a novel model of cell size control, they are similar to previously studied bacteria in that initiation of DNA replication is a key checkpoint for cell division. We compare the regulation of DNA replication initiation and strategies used for cell size homeostasis in mycobacteria and model bacteria. Finally, we review the importance of cellular organization and chromosome segregation relating to the physiology of mycobacteria and consider how new frameworks could be applied across the wide spectrum of bacterial diversity.
模式细菌，如大肠杆菌和枯草芽孢杆菌，会严格调控细胞周期进程，以实现一致的细胞大小分布和复制动态。这些模式细菌的许多标志性特征，包括横向细胞壁伸长以及对称生长和分裂，在分枝杆菌中并不存在。相反，分枝杆菌的生长特征是不对称的极性生长和分裂。这种固有的不对称性使得每个子代细胞在每次分裂时的起始大小和生长速率都不相等，从而产生了表型上的异质群体。尽管分枝杆菌的不对称生长模式导致起始大小的变化比典型的模式细菌群体更大，但细胞大小分布随时间是稳定的。在这里，我们综述了分枝杆菌在面对不对称性和内在异质性时的生长、分裂和细胞周期进程的细胞机制。这些过程共同作用以控制细胞大小。尽管耻垢分枝杆菌和卡介苗（BCG）采用了一种新的细胞大小控制模式，但它们与之前研究的细菌相似之处在于，DNA复制起始是细胞分裂的一个关键检查点。我们比较了分枝杆菌和模式细菌中DNA复制起始的调控以及用于细胞大小稳态的策略。最后，我们综述了细胞组织和染色体分离与分枝杆菌生理学的相关性，并思考如何将新的框架应用于广泛的细菌多样性研究中。
