the spirochete Leptospira spp. can move in liquid and on a solid surface using two periplasmic flagella (pfs), and its motility is an essential virulence factor for the pathogenic species. Mammals are infected with the spirochete through the wounded dermis, which implies the importance of behaviors on the boundary with such viscoelastic milieu; however, the leptospiral pathogenicity involving motility remains unclear. We used a glass chamber containing a gel area adjoining the leptospiral suspension to resemble host dermis exposed to contaminated water and analyzed the motility of individual cells at the liquid-gel border. insertion of one end of the cell body to the gel increased switching of the swimming direction. Moreover, the swimming force of Leptospira was also measured by trapping single cells using an optical tweezer. it was found that they can generate ∼ 17 pN of force, which is ∼ 30 times of the swimming force of Escherichia coli. the force-speed relationship suggested the loaddependent force enhancement and showed that the power (the work per unit time) for the propulsion is ∼ 3.1 × 10-16 W, which is two-order of magnitudes larger than the propulsive power of E. coli. the powerful and efficient propulsion of Leptospira using back-and-forth movements could facilitate their invasion. Motility has been identified as a crucial virulence factor for pathogenic bacteria 1. For example, a motility-deficient mutant of Vibrio cholerae is attenuated due to the decreased invasion efficiency of the epithelium 2. In some flagellated bacteria, both motility and flagella are considered essential as an adhesin. For example, Salmonella enterica attaches to the host tissue via peritrichous flagella, which results in colonization and clinical outcomes 3. Although spirochetes, such as Borrelia burgdorferi (the Lyme disease) 4 and Brachyspira hyodysenteriae (swine dysentery) 5 , also utilize motility during infection, their flagella exist beneath the outer membrane, which is known as the periplasmic flagella (PFs), and spirochetal flagella are not directly involved in pathogenicity. Instead, the improvement of swimming ability 6 and diverse adherence 7 in viscoelastic environments is believed to be responsible for their colonization and dissemination within hosts. The genus Leptospira is a member of spirochetes, and these pathogenic species have been found to cause a worldwide zoonosis known as leptospirosis. Pathogenic Leptospira cells are maintained in the proximal renal tubules of rodents as a reservoir. When the hosts urinate, they spread the spirochetes into the environment; as a result, many mammals, including humans, are percutaneously or transmucosally infected by contact with the contaminated soil and water 8,9. Leptospira spp. have a right-handed spiral cell body and exhibit curvatures at both ends (Fig. 1A). Spirochetes can swim in liquid and crawl on surfaces using two PFs (one PF/cell end) (Fig. 1B). The morphology of the cell ends frequently changes between a spiral and a hook shape; and there is an asymmetri...
The spirochete Leptospira spp. can move in liquid and on a solid surface with two periplasmic flagella (PFs), and the motility is essential virulence factor for the pathogenic species. Although the fact that mammals are infected with the spirochete through wounded dermis imply the importance of behaviors on the boundary with such viscoelastic milieu, how the leptospiral pathogenicity involves motility remains unclear. We used the glass chamber containing a gel area adjoining the leptospiral suspension to resemble host dermis exposed to contaminated water and analyzed the motility of individual cells at the liquid-gel border. Insertion of one end of the cell body to the gel increased switching of the swimming direction. We also measured the swimming force of Leptospira by trapping single cells using optical tweezer, showing that they can produce ~17 pN, which is ~30 times of the swimming force of Escherichia coli. The force-speed relationship suggested the load-dependent force enhancement and showed that the power (the work per unit time) for the propulsion is ~3.1×10 -16 W, which is two-order larger than the propulsive power of E. coli. Powerful, efficient propulsion of Leptospira with back-andforth movements enabling them to explore invasion routes could facilitate percutaneous infection.
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