One example is Aquaspirillum magnetotacticum , which has magnetosomes. The microbe uses this to determine which way is up and that helps it to find nutrients or adjust its depth in an aquatic environment. In these cases they are used for navigation on long migrations. Chemotaxis Chemotaxis is accomplished by sensing the environment and adjusting the rotation of the flagella in response to stimuli. Before we get into this, I will point out that most of this work has been done on E. coli .
Chemotaxis can behave slightly differently in other microbes.
Flagella can rotate clockwise or counterclockwise. When flagella rotate counterclockwise this creates a force pushing on the bacteria. In the case of E. coli the peritrichous flagella bunch together and all push from one side. This causes the bacteria to move in a straight line, called a run. When flagella rotate clockwise, they all pull on the microbe.