Asymmetric cell division in Mycobacterium tuberculosis and its unique features
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ORIGINAL PAPER
Asymmetric cell division in Mycobacterium tuberculosis and its unique features Srinivasan Vijay · Mukkayyan Nagaraja · Jees Sebastian · Parthasarathi Ajitkumar
Received: 1 August 2013 / Revised: 6 November 2013 / Accepted: 18 January 2014 / Published online: 31 January 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Recently, several reports showed that about 80 % of mid-log phase Mycobacterium smegmatis, Mycobacterium marinum, and Mycobacterium bovis BCG cells divide symmetrically with 5–10 % deviation in the septum position from the median. However, the mode of cell division of the pathogenic mycobacterial species, Mycobacterium tuberculosis, remained unclear. Therefore, in the present study, using electron microscopy, fluorescence microscopy of septum- and nucleoid-stained live and fixed cells, and live cell time-lapse imaging, we show the occurrence of asymmetric cell division with unusually deviated septum/constriction in 20 % of the 15 % septating M. tuberculosis cells in the mid-log phase population. The remaining 80 % of the 15 % septating cells divided symmetrically but with 2–5 % deviation in the septum/constriction position, as reported for M. smegmatis, M. marinum, and M. bovis BCG cells. Both the long and the short portions of the asymmetrically dividing M. tuberculosis cells with unusually deviated septum contained nucleoids, thereby generating viable short and long cells from each asymmetric division. M. tuberculosis short cells were acid fast positive and, like the long cells, further readily underwent growth and division to generate micro-colony, thereby showing that they were neither mini cells, spores nor dormant forms of mycobacteria. The freshly diagnosed pulmonary Communicated by Erko Stackebrandt. Electronic supplementary material The online version of this article (doi:10.1007/s00203-014-0953-7) contains supplementary material, which is available to authorized users. S. Vijay · M. Nagaraja · J. Sebastian · P. Ajitkumar (*) Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, Karnataka, India e-mail: [email protected]
tuberculosis patients’ sputum samples, which are known for the prevalence of oxidative stress conditions, also contained short cells at the same proportion as that in the midlog phase population. The probable physiological significance of the generation of the short cells through unusually deviated asymmetric cell division is discussed. Keywords Asymmetric septum · Asymmetric cell division · Mycobacterium tuberculosis · Short cell · Nucleoid · Symmetric cell division
Introduction Symmetric binary fission is the hallmark of rod-shaped bacteria to generate two equally sized daughter cells. For instance, symmetric binary fission with the septum precisely placed at the mid-cell site occurs in Escherichia coli (Yu and Margolin 1999) and Bacillus subtilis (Migocki et al. 2004). Both the pathogenic and the non-pathogenic mycobacterial species also have been found to divide through symmetric binary fission (see H
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