MUTATIONAL ANALYSIS OF THE BORDETELLA-PERTUSSIS FIM FHA GENE-CLUSTER - IDENTIFICATION OF A GENE WITH SEQUENCE SIMILARITIES TO HEMOLYSIN ACCESSORY GENES INVOLVED IN EXPORT OF FHA/

The chromosome of Bordetella pertussis harbours a region of 27 contigu ous kb, which contains the bvg, fha and fim genes, involved in the co- ordinate regulation of virulence genes, FHA production and fimbriae pr oduction, respectively. The linkage of FHA and fimbrial genes has resu lted in some confusion concerning the existence and location of genes required for the production of FHA and the function of the fimbrial ge nes fimB-D, which were proposed to be involved in both FHA and fimbria e biosynthesis. Through the use of non-polar mutations in each of thes e genes, we found that fimB-D are required for the production of both serotype 2 and 3 fimbriae, but not for FHA biosynthesis. Furthermore, a large open reading frame, designated fhaC, was identified downstream of fimD. It was shown that fhaC is essential for FHA production but n ot for fimbriae biogenesis. We propose that insertion mutations in fim B-D affect FHA production because of polar effects on fhaC expression. An insertion in the region downstream of fhaC had only a slight effec t on FHA and fimbriae production. The fhaC gene product shows homology with ShlB and HpmB, two outer membrane proteins involved in export an d activation of the haemolysins, ShlA and HpmA, of Serratia marcescens and Proteus mirabilis, respectively. Homology is also observed betwee n the N-termini of FHA, ShlA and HpmA. Export of the haemolysins requi res the N-termini of these molecules, and when this region was removed from FHA by an in-frame deletion, FHA biosynthesis was abolished. The se results suggest that the N-terminus of FHA interacts with FhaC, and that as a result FHA is transported across the outer membrane.