PILT MUTATIONS LEAD TO SIMULTANEOUS DEFECTS IN COMPETENCE FOR NATURALTRANSFORMATION AND TWITCHING MOTILITY IN PILIATED NEISSERIA-GONORRHOEAE

Neisseria gonorrhoeae, the Gram-negative aetiological agent of gonorrh oea, is one of many mucosal pathogens of man that expresses competence for natural transformation. Expression of this phenotype by gonococci appears to rely on the expression of type IV pill (Tfp), but the mech anistic basis for this relationship remains unknown. During studies of gonococcal pilus biogenesis, a homologue of the PilT family of protei ns, required for Tfp-dependent twitching motility in Pseudomonas aerug inosa and social gliding motility in Myxococcus xanthus, was discovere d. Like the findings in these other species, we show here that gonococ cal pilT mutants constructed in vitro no longer display twitching moti lity, In addition, we demonstrate that they have concurrently lost the ability to undergo natural transformation, despite the expression of structurally and morphologically normal Tfp, These results were confir med by the findings that two classes of spontaneous mutants that faile d to express twitching motility and transformability carried mutations in pilT. Piliated pilT mutants and a panel of pilus assembly mutants were found to be deficient in sequence-specific DNA uptake into the ce ll, the earliest demonstrable step in neisserial competence. The PilT- deficient strains represent the first genetically defined mutants that are defective in DNA uptake but retain Tfp expression.