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Abstract
Mycobacteria are members of the actinomycetes that grow by tip extension and lack apparent homologues of the known cell division regulators found in other rod-shaped bacteria. Previous work using static microscopy on dividing mycobacteria led to the hypothesis that these cells can grow and divide asymmetrically, and at a wide range of sizes, in contrast to the cell growth and division patterns observed in the model rod-shaped organisms. In this study, we test this hypothesis using live-cell time-lapse imaging of dividing Mycobacterium smegmatis labelled with fluorescent PBP1a, to probe peptidoglycan synthesis and label the cell septum. We demonstrate that the new septum is placed accurately at mid-cell, and that the asymmetric division observed is a result of differential growth from the cell tips, with a more than 2-fold difference in growth rate between fast and slow growing poles. We also show that the division site is not selected at a characteristic cell length, suggesting this is not an important cue during the mycobacterial cell cycle.
Highlights
Cell growth and division are fundamental processes to all life and contribute to the morphological diversity observed across the prokaryote kingdom
Investigations into cell growth and division in bacteria have largely concentrated on a few model organisms, including Bacillus subtilis and Escherichia coli
To confirm our original observations of eccentrically placed internal vancomycin spots and variable cell lengths, we collected numerical data from M. smegmatis mc2155 [42], M. smegmatis NC08519, M. bovis BCG, and C. glutamicum stained with Van-BODIPY
Summary
Cell growth and division are fundamental processes to all life and contribute to the morphological diversity observed across the prokaryote kingdom. Bacterial shape is determined and maintained by the rigidity of the peptidoglycan cell wall [2,3,4], the growth of which is controlled by directing peptidoglycan synthesis to specific sites within the cell [5]. These two rod-shaped bacteria control growth and division by similar mechanisms, using MreB to spatially regulate peptidoglycan synthesis [6]; while the Min proteins and nucleoid occlusion proteins ensure division occurs at mid-cell [7,8,9]. Thought to polymerize into a helical structure along the length of the cell to act as a scaffold for the peptidoglycan synthesis machinery [6], MreB has recently been shown to form mobile, fragmented elongation complexes that insert new peptidoglycan [11,12]
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