Controlling Production with Small Numbers: Precision Apparatuses Made of Proteins at Work in Bacteria

Abstract

Many bacteria that cause disease in humans and animals, such as salmonella, pathogenic Escherichia coli O157, and Vibrio cholerae, move by rotating their flagella, which are fibrous locomotor apparatuses growing from their bodies, resembling screws. Though the thickness of a flagellum is only 1/4000 that of a hair, an enlarged view with an electron microscope reveals that a flagellum has a machine-like appearance. A flagellum is a complex device made of a combination of roughly 30 types of protein molecules. Parts can contain as few as 1–5 protein molecules or as many as tens of thousands. Cells have various infinitesimally small complex apparatuses which, like flagella, are composed of an aggregation of protein molecules and support biological activity. When these devices are needed, only the exact number needed is made, thus enabling them to function well. The production of these apparatuses is regulated by proteins; in the case of flagella, production is regulated by a small number of proteins called export chaperones. Here, we examine how bacterial flagella are made through a conversation between Shun, a high school student who unfortunately contracted food poisoning, and Maiko, the school nurse.