Read more: 鈥�Not so simple: Bugs that break all the rules鈥�
The textbook bacterium has a thick wall and not much else to give it structure 鈥� but it turns out that protein skeletons and compartments are common
Complex cells like the ones that make our bodies can form all kinds of different shapes even though they are enclosed only by a soft membrane. The secret is their internal skeleton, or cytoskeleton, a scaffold that is continually adjusted by adding or taking away segments. It not only maintains a cell鈥檚 shape, it even functions as a railway for transporting molecules around the cell and also ensures everything ends up in the right place when cells divide.
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It was long assumed that bacteria, which are surrounded by a thick, rigid wall, have no need of such a sophisticated piece of kit. But in recent years it has emerged that many bacteria and archaea 鈥� the other branch of simple cells 鈥� have their own versions of the proteins that form the cytoskeleton.
In at least some bacteria these proteins form a cytoskeleton that does much the same job as in complex cells, such as maintaining the rod shape of cells like E. coli. The cytoskeleton also helps anchor structures such as the whip-like flagella that some bacteria use to swim. And in magnetotactic bacteria, cytoskeletal proteins keep the magnetic particles inside them aligned, allowing the entire cell to act as a living compass needle.
Internal compartments
According to the textbooks, only complex cells have internal compartments, or organelles, but numerous exceptions to this rule are being discovered. For instance, a quarter of the bacteria that have had their genomes sequenced have the genes for making 鈥渕颈肠谤辞肠辞尘辫补谤迟尘别苍迟蝉鈥� 鈥� tiny chemical factories that speed up reactions by concentrating the reactants and also help protect the rest of the cells from toxic by-products. The first to be discovered were the carboxysomes of cyanobacteria, which boost the efficiency of photosynthesis.
Other bacteria have internal stores rather than factories. Photosynthetic bacteria and archaea often have little internal bubbles, called gas vesicles, to make them buoyant.
The 鈥渙rganelles鈥� within bacteria are usually made of proteins and have regular geometrical shapes, like the shells of viruses. However, a few do have membrane-bound compartments like those of complex cells. Several sulphur-eating bacteria store nitrate in internal vacuoles, for instance, including Thiomargarita namibiensis.
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