RESEARCH HIGHLIGHTS

Nature Reviews Microbiology | Published online 30 Aug 2016; doi:10.1038/nrmicro.2016.128

CELLULAR MICROBIOLOGY How pathogens divide In most bacteria, cell division occurs LPS and subdomains of the bacterial corresponded to the mid-cells of the by binary fission, which is directed by chromosome. The process of cell daughter cells. Indeed, observation the cell FtsZ at the mid-cell. Alternatively, in division was initiated by budding of of the daughter cells following cell division site is Actinobacteria, cell division is polar- the membrane at one of the poles division showed that these zones created in the ized and is dependent on the DivIVA and was asymmetric, in that the remained active as mid-cell elonga- complex. However, very few studies inheritance of cellular components tion zones, suggesting that, unusually, grandparent, have examined cell division outside was uneven between the mother cell B. burgdorferi cells mark the sites rather than of the context of model bacteria. and the newly formed daughter cell. at which the next generation will the parent, of Now, Abdelrahman et al. and Jutras, However, by the time of cell division, divide before dividing themselves. Scott et al. describe the biology of cell which occurred at a septum that was Observations of two other pathogens the daughter division in Chlamydia trachomatis formed during the budding process, from the genus, Borrelia hermsii cell and Borrelia burgdorferi, respectively, the cellular content and sizes of the and Borrelia miyamotoi, revealed a and reveal novel features of how cells mother and daughter cells were similar elongation pattern; however, divide in each of these important similar to one another. the mode of elongation did not seem human pathogens. In contrast to C. trachomatis, the to be conserved in other spirochete Intriguingly, C. trachomatis lacks Lyme disease spirochete B. burg- genera and may therefore be unique homologues of FtsZ or DivIVA, and dorferi divides by FtsZ-dependent to Borrelia spp. so cell division must differ in some binary fission. However, little is In each of the two studies, novel way from the mechanisms that have known about cellular division in this features of cell division were uncov- been described in other bacteria. species (or, indeed, in spirochetes ered by investigating the full cell Although some microscopy reports more generally), in part owing to the cycle. For C. trachomatis, daughter have suggested that C. trachomatis challenge of studying slow-growing cells that resemble those produced by cells divide by binary fission, the bacteria that have little genetic binary fission were found to instead mechanism has remained unclear, in tractability. Jutras, Scott et al. used be produced by budding from a pole. part owing to the lack of amenability fluorescent d-alanine analogues to For B. burgdorferi, binary fission does of obligate intracellular pathogens to image peptidoglycan synthesis in occur, but the cell division site is cre- laboratory study. Surprisingly, when B. burgdorferi, which showed that the ated in the grandparent, rather than Abdelrahman et al. used confocal elongation of the cell wall prior to cell the parent, of the daughter cell. microscopy to image C. trachomatis division occurred in three discrete Naomi Attar

growth in HeLa cells, they found zones. Although elongation was ORIGINAL ARTICLES Abdelrahman, Y. et al. that cell division occurred at the cell concentrated at the mid-cell for most Polarized cell division of Chlamydia trachomatis. poles. Cell growth prior to division of the cell cycle, the two additional PLoS Pathog. 12, e1005822 (2016) | Jutras, B. L., Scott, M. et al. Lyme disease and relapsing fever was characterized by a polarized zones of elongation were observed Borrelia elongate through zones of peptidoglycan distribution of cellular shortly prior to cell division, which synthesis that mark division sites of daughter cells. Proc. Natl Acad. Sci. USA 113, 9162–9170 (2016) components, was concomitant with the initiation FURTHER READING Haeusser, D. P. & Margolin W. including the of nucleoid separation and septa- Splitsville: structural and functional insights into major outer tion. Interestingly, the locations the dynamic bacterial Z ring. Nat. Rev. Microbiol. 14, 305–319 (2016) NPG membrane protein, of the additional elongation zones

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