Most impressively, a recently discovered wall-less organism in the Red Sea actively changes from a long straight filament to one with bumps, curls, curves and tightly wound spirals ( 3). This assertion needs to be qualified and explained, because bacteria without such walls also have complicated morphologies ( 57, 82). Because the scope could quickly get out of hand, the discussion will center exclusively on how rod shaped cells set their dimensions and will draw primarily from research on three model organisms: Escherichia coli, Bacillus subtilis, and Caulobacter crescentus.Ĭell shape is often stated to be “determined” by the cell wall, and especially by the peptidoglycan layer. Here, I wish to highlight some current questions and challenges, to rescue data and ideas in danger of being forgotten or ignored, and to broaden our view about the approaches available for answering questions about basic cell dimensions. Good evidence addresses mechanisms that affect cell length, but we have little idea about how bacteria set their diameter. Instead of emphasizing how bacteria create their overall shapes, the present article will concentrate on how they determine their fundamental dimensions of length and diameter. Of special importance are those reviews describing bacterial cytoskeleton proteins that are critical for driving cell wall synthesis and regulating its localization ( 13, 32, 60, 75, 92). Other reviews are similarly educational and readable, and should be consulted for more detail about how bacteria select the site of cell division ( 10) and how they create cells that are rod shaped ( 12, 15, 23, 107), coccoid ( 109) or spiraled ( 25, 104). 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.įor a superb introduction to the results, interpretations and ideas that form the foundation of the current view of how bacteria assemble well-defined structures, I recommend the overview provided by W.

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. Despite intermittent progress, only in the last decade have we begun to understand in any real depth how they do so. Of course, bacteria have been doing this for some billions of years. 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. Nanotechnologists want to fabricate the tiniest structures possible or, even better, the tiniest possible machines. On the small side of this equation, the science of nanotechnology attracts people with the most audacious dreams. One of humanity's drives is to make things, allied with the curious penchant for wanting to make them larger or smaller.

Bacteria shapes diagram