pilQ missense mutations have diverse effects on PilQ multimer formation, piliation, and pilus function in Neisseria gonorrhoeae

Northwestern University, Feinberg School of Medicine, Department of Microbiology-Immunology

^* To whom correspondence should be addressed. Email: h-seifert{at}northwestern.edu.

	Abstract

Type IV pili are required for virulence of Neisseria gonorrhoeae, as they are involved in adherence to host-epithelium, twitching motility, and DNA transformation. The outer membrane secretin PilQ forms a homo-dodecameric ring through which the pilus is proposed to be secreted. pilQ null mutants are nonpiliated and thus, all pilus-dependent functions are abrogated. Mutagenesis was performed on the middle one-third of pilQ, and mutants with a colony morphology consistent with nonpiliated or under-piliated bacteria were selected. Nineteen mutants, each with a single amino acid substitution, were isolated and displayed diverse phenotypes in terms of PilQ multimer stability, pilus expression, transformation efficiency, and host-cell adherence. The 19 mutants were grouped into five phenotypic classes based on functionality. Four of the five mutant classes fit the current model of pilus functionality, which proposes that a functional pilus assembly apparatus, not necessarily full-length pili, are required for transformation, while high levels of displayed pili are required for adherence. One class, despite having an under-piliated colony morphology, expressed high levels of pili yet adhered poorly, demonstrating that pilus expression is necessary but not sufficient for adherence, and indicating that PilQ may be directly involved in host-cell adherence. The collection of phenotypes expressed by these mutants suggests that PilQ has an active role in pilus expression and function.