Bacterial shape: questions and possibilities

Haloquadratum walsbyi One of humanity’s drives is to make things, allied with the curious desire to want to make them larger or smaller. On the small side of this equation, the science of nanotechnology attracts people with audacious dreams. Nanotechnologists want to fabricate the tiniest structures possible or, even better, the tiniest possible machines. The overarching desire is to create molecular sized devices of strictly defined dimensions, with little variation among the new entities, and to be able to produce multitudes over and over with few failures. Of course, bacteria have been doing this for some billions of years. Despite intermittent progress, only in the last decade have we begun to understand in any real depth how they do so.

The question that dominated discussion in this field 15–20 years ago was, How does a bacterium find its middle? That question seems well on its way to being answered. The new fundamental question about bacterial shape is, How does a bacterium construct a cell having a defined length, diameter, and overall geometry? Technical and genetic advances have finally made this question amenable to experiment and have reinvigorated the application of new forms of microscopic visualization.

Bacterial shape: two-dimensional questions and possibilities. (2010) Annu Rev Microbiol. 64: 223-240
Events in the past decade have made it both possible and interesting to ask how bacteria create cells of defined length, diameter, and morphology. The current consensus is that bacterial shape is determined by the coordinated activities of cytoskeleton complexes that drive cell elongation and division. Cell length is most easily explained by the timing of cell division, principally by regulating the activity of the FtsZ protein. However, the question of how cells establish and maintain a specific and uniform diameter is, by far, much more difficult to answer. Mutations associated with the elongation complex often alter cell width, though it is not clear how. Some evidence suggests that diameter is strongly influenced by events during cell division. In addition, surprising new observations show that the bacterial cell wall is more highly malleable than previously believed and that cells can alter and restore their shapes by relying only on internal mechanisms.

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