Submitted to: Journal of Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2000
Publication Date: N/A
Interpretive Summary: Many bacteria are able to swim. It has been known for several decades that swimming helps bacteria move to favorable locations in their environment. For bacteria causing animal and human diseases, swimming is important because they can move to locations in the body where they cause disease. Unfortunately, we don't completely understand how bacteria swim, especially those corkscrew-shaped bacteria known as spirochetes. The spirochetes cause important diseases such as syphilis and Lyme disease of humans and dysentery of animals. The spirochete that causes swine dysentery is named Brachyspira hyodysenteriae. There are no effective commercial vaccines for these diseases. Many bacteria twirl long whip-like appendages for swimming. These whip-like appendages are called flagella. This article describes research to determine how flagella are made by Brachyspira hyodysenteriae. We discovered that changing flagellar proteins named FlaB did not affect flagellar shape. However, changing a flagellar protein named FlaA affected the shape of the flagella and made the flagella thinner. Additionally, the FlaA proteins form an outer wrapping or sheath around the outside of the flagellum. These findings are important because they contribute to our basic understanding of bacterial swimming. Understanding how disease-causing bacteria are able to swim could lead to new methods for preventing disease. The information in this manuscript is important to research scientists and industry scientists designing vaccines and drugs.
Technical Abstract: Spirochete periplasmic flagella (Pfs) have a unique structure. In most spirochete species, the periplasmic flagellar filaments consist of a core of at least three proteins (FlaB1, FlaB2, and FlaB3) and a sheath protein (FlaA). Each of these proteins is encoded by a separate gene. Using Brachyspira hyodysenteriae as a model system for PF function, we analyzed purified PFs from previously constructed flaA::cat, flaA::kan, and flaB1::kan mutants and newly constructed flaB2::cat and flaB3::cat mutants. We investigated whether any mutants had a loss of motility and altered PF structure. As formerly found with flaA::cat, flaA::kan, and flaB1::kan mutants, flaB2::cat and flaB3::cat mutants were less motile than the wild-type strain, using a swarm-plate assay. SDS-PAGE and Western blot analysis indicated that each mutation resulted in the specific loss of the cognate gene product in the assembled purified PFs. Consistent with these results, Northern blots indicated that each flagellar filament gene was monocistronic. In contrast to previous results, purified PFs from a flaA::cat mutant were significantly thinner (19.6 nm) than those of the wild-type and flaB1::kan, flaB2::cat, and flaB3::cat mutants (24 to 25 nm). These results provide supportive genetic evidence that FlaA forms a sheath around the FlaB core. Using high-magnification dark-field microscopy, we also found that flaA::cat and flaA::kan mutants produced PFs with a smaller helix pitch and helix diameter compared to the wild-type strain and flaB mutants. These results indicate that the interaction of FlaA with the FlaB core impacts periplasmic flagellar helical morphology.