Dynamics of Neisseria gonorrhoeae Attachment: Microcolony Development, Cortical Plaque Formation, and Cytoprotection

Abstract

Neisseria gonorrhoeae is the bacterium that causes gonorrhea, a major sexually transmitted disease and a significant cofactor for human immunodeficiency virus transmission. The retactile N. gonorrhoeae type IV pilus (Tfp) mediates twitching motility and attachment. Using live-cell microscopy, we reveal for the first time the dynamics of twitching motility by N. gonorrhoeae in its natural environment, human epithelial cells. Bacteria aggregate into microcolonies on the cell surface and induce a massive remodeling of the microvillus architecture. Surprisingly, the microcolonies are motile, and they fuse to form progressively larger structures that undergo rapid reorganization, suggesting that bacteria communicate with each other during infection. As reported, actin plaques form beneath microcolonies. Here, we show that cortical plaques comigrate with motile microcolonies. These activities are dependent on pilT, the Tfp retraction locus. Cultures infected with a pilT mutant have significantly higher numbers of apoptotic cells than cultures infected with the wild-type strain. Inducing pilT expression with isopropyl-␤-D-thiogalactopyranoside partially rescues cells from infection-induced apoptosis, demonstrating that Tfp retraction is intrinsically cytoprotective for the host. Tfp-mediated attachment is therefore a continuum of microcolony motility and force stimulation of host cell signaling, leading to a cytoprotective effect.Type IV pili (Tfp) are filamentous appendages expressed by a wide range of bacteria, including Synechocystis spp., Pseudomonas aeruginosa, Myxococcus xanthus, Xylella fastidiosa, Clostridium perfringens, enterohaemorrhagic and enteropathogenic Escherichia coli, Neisseria meningitidis, and Neisseria gonorrhoeae (29,32,37,50,54,56,61). The Tfp of several of these bacteria are known to retract, and retraction underlies twitching motility, DNA uptake, phage sensitivity, and social behavior, such as fruiting-body and biofilm formation.N. gonorrhoeae, the bacterium that causes gonorrhea, expresses multiple nonpolar retractile Tfp that promote attachment to epithelial cells (38). Retraction requires the ATPase PilT, which is proposed to disassemble the Tfp fiber (2,13,15). N. gonorrhoeae pilT null mutants express nonretractile Tfp (38,60). Cycles of Tfp extension, substrate tethering, and retraction enable N. gonorrhoeae to crawl on a glass coverslip or agar surface (twitching motility) (34). Twitching motility on epithelial cells has not been studied. Understanding N. gonorrhoeae motility behavior in this environment is important, as the bacterium infects only humans and cannot survive outside the human body.Mechanical forces of 50 to 100 pN are generated by the retraction of a Tfp fiber (24, 38). Thus, Tfp retraction allows N. gonorrhoeae to pull and exert physical stress on its substrate. Tfp retraction induces a number of responses in the infected epithelial cell. It triggers Ca 2ϩ and stress kinase signaling, cytoskeletal rearrangements, and cortical plaque formation and regulates epithelial gen...

Influence of type IV pilus retraction on the architecture of the Neisseria gonorrhoeae-infected cell cortex

“…The relationship between the cortical plaque and the microcolony is dynamic. As the microcolony crawls over the cell surface, the cortical plaque migrates with it (Higashi et al, 2007).…”

“…Repeated cycles of Tfp extension, substrate attachment and Tfp retraction allow GC to crawl over surfaces and aggregate into microcolonies. Tfp retraction from bacteria in a microcolony allows the community to crawl over the epithelial cell surface and fuse with other microcolonies to form larger motile structures (Higashi et al, 2007).…”

“…The relationship between the cortical plaque and the microcolony is dynamic. As the microcolony crawls over the cell surface, the cortical plaque migrates with it (Higashi et al, 2007).The microcolony-host cell interface is therefore an important focus of study.A number of microscopy studies have provided important information on the ultrastructure of the infected host cell surface (Edwards et al, 2000;Evans, 1977;Griffiss et al, 1999;McGee et al, 1981;Mosleh et al, 1997;Stephens, 1989;Tjia et al, 1988;Ward et al, 1974). Microvilli are numerous at sites of infection, and they appear to be elongated and deformed.…”

“…Repeated cycles of Tfp extension, substrate attachment and Tfp retraction allow GC to crawl over surfaces and aggregate into microcolonies. Tfp retraction from bacteria in a microcolony allows the community to crawl over the epithelial cell surface and fuse with other microcolonies to form larger motile structures (Higashi et al, 2007).Abbreviations: GC, gonococcus (Neisseria gonorrhoeae); DAPI, 49,6-diamidino-2-phenylindole; Tfp, type IV pili; SEM, scanning electron microscopy; TEM, transmission electron microscopy; wt, wild-type. Shaw & Falkow, 1988).…”

Pili de type IV

“…Mais il ne faut pas oublier que les humaines. Nombre de modifications des cellules humaines associées à l'infection par Neisseria ne se font plus [7,8]. L'expression génique des cellules humaines en réponse à l'infection est aussi fortement modifiée en présence ou en l'absence de force mécanique [9].…”