Bacterial motility and chemotaxis: light-induced tumbling response and visualization of individual flagella.

Abstract High intensity visible light induces tumbling in Salmonella typhimurium , the effect being reversible provided short pulses are used. Fully aerated cultures are more sensitive to light than cultures with a lower oxygen tension. Bacteria which have been subjected to a sufficient positive chemotactic stimulus (concentration increase of attractant) are immune to the light stimulus. Light with a wavelength of 510 nm or shorter is effective, suggesting that absorption by a flavin may be involved. The light source used, with a yellow filter inserted to prevent light-induced tumbling, is bright enough to allow visualization of individual flagella as well as flagellar bundles. This has provided information on flagellar aggregation, rigidity, and behavior during tumbling. Since the occurrence of tumbles is modified as a result of chemical gradient sensing, these techniques are valuable in the study of bacterial chemotaxis.