Type IV Secretion Machinery Promotes Ton-Independent Intracellular Survival of Neisseria gonorrhoeae within Cervical Epithelial Cells

Abstract

Survival of Neisseria gonorrhoeae within host epithelial cells is expected to be important in the pathogenesis of gonococcal disease. We previously demonstrated that strain FA1090 derives iron from a host cell in a process that requires the Ton complex and a putative TonB-dependent transporter, TdfF. FA1090, however, lacks the gonococcal genetic island (GGI) that is present in the majority of strains. The GGI in strain MS11 has been partially characterized, and it encodes a type IV secretion system (T4SS) involved in DNA release. In this study we investigated the role of iron acquisition and GGI-encoded gene products in gonococcal survival within cervical epithelial cells. We demonstrated that intracellular survival of MS11 was dependent on acquisition of iron from the host cell, but unlike the findings for FA1090, expression of the Ton complex was not required. Survival was not dependent on a putative TonB-like protein encoded in the GGI but instead was directly linked to T4SS structural components in a manner independent of the ability to release or internalize DNA. These data suggest that expression of selected GGI-encoded open reading frames confers an advantage during cervical cell infection. This study provides the first link between expression of the T4SS apparatus and intracellular survival of gonococci.Neisseria gonorrhoeae is the causative agent of the sexually transmitted infection gonorrhea. Although symptomatic urethritis is the most common presentation in men, asymptomatic infections associated with cervical acquisition in women can lead to ascension of the bacteria to the upper reproductive tract. In this context, an understanding of the immune evasion tactics employed by this organism is essential for eliminating potential downstream sequelae, including disseminated gonococcal infection, pelvic inflammatory disease, infertility, and ectopic pregnancy (23,45). The outcome of gonococcal infections and the resulting clinical manifestations elicited are determined, in part, by strain-specific factors. The differences are expected to impact host-pathogen interactions that occur at the primary site of infection, the urogenital epithelium.Productive gonococcal infections require that the bacteria circumvent the innate iron-withholding mechanisms employed by the human host. Moreover, epithelial cell responses to Neisseria infection, including reduced expression of the transferrin receptor gene and diminished transferrin receptor cycling, which result in further limitation of iron availability, have been described previously (8,9,34). As the ability to acquire iron from the human host is a key determinant in gonococcal pathogenesis (1,15), N. gonorrhoeae has evolved numerous mechanisms to acquire this required nutrient in an iron-depleted environment. Various iron uptake systems that are thought to promote gonococcal replication in extracellular niches have been characterized (42). Specifically, these systems hijack iron from the host proteins transferrin (14), lactoferrin (7), and hemoglobin (12) in a ma...

Legionella pneumophila LbtU Acts as a Novel, TonB-Independent Receptor for the Legiobactin Siderophore

“…Some bacteria have more than one tonB or tonB-like gene, and in all cases, the connection between TonB-ExbBD and iron acquisition, when examined, has been clear (1,4,10,29,39,58,59,64,93,97,121,126,139). But recently, it has become apparent that some bacteria that contain an OM and IM, including L. pneumophila, and species of Chlamydia, Chlamydophila, Coxiella, Ehrlichia, Francisella, and Rickettsia do not have TonB-ExbBD (29,74).…”

Mating Pair Formation Homologue TraG Is a Variable Membrane Protein Essential for Contact-Independent Type IV Secretion of Chromosomal DNA by Neisseria gonorrhoeae

“…Named VirB6 in A. tumefaciens and the related systems, these homologues are also inner-membrane proteins and interact with other proteins of their T4SSs (55)(56)(57). A. tumefaciens VirB6 interacts directly with inner-membrane protein VirB8 and stabilizes VirB3 and VirB5 in the secretion apparatus (63,64,66,67). A. tumefaciens VirB6 can be cross-linked to DNA using the TrIP method (58).…”

Prevalence and Detailed Mapping of the Gonococcal Genetic Island in Neisseria meningitidis

“…Intracellular growth in the absence of inorganic iron was assayed using a modification of the method described by Zola et al (42). ME180 cervical epithelial cells were seeded at a density of 2.5 ϫ 10 5 cells/ml to a 12 well plate and grown to 70 to 80% confluence at 37°C with 5% CO 2 in McCoy's 5A medium (Gibco) supplemented with 10% heat-inactivated fetal bovine serum (HI-FBS) (Gibco).…”

“…The seventh strain we identified as possessing a distinct GGI type during the course of this study. The GGI-encoded T4SS in N. gonorrhoeae has been shown to secrete DNA active in natural transformation and to facilitate TonB-independent iron uptake during intracellular growth of gonococci (42). Thus, the presence of the T4SS genes in Mc might affect horizontal gene transfer or intracellular growth of N. meningitidis strains possessing the T4SS genes.…”