As discussed earlier, motile bacteria move via rotation of one or more flagella, turning counter-clockwise when swimming and clockwise when tumbling. Apparently, there must be some type of mechanisms and driving force for this flagellular movement and rotational switch. Eukaryotic organisms with flagella use ATP as the energy source for the movement of their flagella. When the environment was deficient in an electrochemical proton gradient, however, flagellular movement stopped. The actual rotation of the flagellum is controlled by protein complexes located in the basal body of the flagellum.
Optimal rotation is achieved when all eight complexes of the flagellum are functioning.
Mechanisms of Chemotaxis Now that it has been established that some bacteria are chemotactic toward and away from certain chemicals and the mechanisms by which actual movement occurs, we must address the question of what the bacteria detect and how. He found that bacteria that were attracted to certain chemicals showed no chemotactic attraction to the metabolized products of those attractants. By working with certain mutant strains of E. coli, he found that the detection of these attractants and repellants was due to certain sensory proteins he termed chemoreceptors. Later work identified the genes for these chemoreceptors, as well as the receptors themselves. I binds serine as well as certain repellants and is encoded for by the tsr gene.