Evidence for specificity in type 4 pilus biogenesis by enteropathogenic Escherichia coli

Type 4 fimbriae (pili) are surface appendages that are expressed by many sp ecies of Gram-negative bacteria. Previous studies have demonstrated that Ps eudomonas aeruginosa can express and assemble pilin subunits from several u nrelated species, indicating a common mechanism for biogenesis of type 4 pi ll whereby structural subunits from one system may be interchanged with tho se of another. In this study, an isogenic mutant of enteropathogenic Escher ichia coli (EPEC) was constructed containing the entire tcpA gene from Vibr io cholerae O395, which encodes the major structural subunit of the toxin-c oregulated pilus (TCP). in place of bfpA, which encodes the major structura l subunit of the bundle-forming pilus (BFP), Surprisingly. expression of ty pe 4 pilin structures and the associated phenotype of bacterial autoaggrega tion in culture media were not observed for cells of the EPEC strain contai ning tcpA nor for those containing an additional mutation in bfpF. which ot herwise is associated with a hyperfimbriate phenotype, In addition. cells o f a bfpA mutant EPEC strain containing plasmids designed to express either of two different chimeric type 4 pilin subunits containing segments of BfpA and TcpA also failed to form bacterial aggregates and express type 4 pilin structures. Collectively. these results indicate that the type 4 pilin ass embly system of SPEC exhibits specificity with regard to pilin subunit reco gnition and assembly.