The Bpel locus encodes type III secretion machinery in Bordetella pertussis

Abstract

Type III secretory genes(Bscl, J, K, L, N and O) have recently been identified in Bordetella bronchiseptica and shown to be under the control of the BvgAS locus. We examined a 35 616 byte DNA sequence amplified from Bordetella pertussis Tohama I for homology with known type III secretory genes in Yersinia spp. and Pseudomonas sppand a total of 20 homologous open reading frames were detected. Putative type III secretion proteins in B. pertussis were designated according to their homology with type III secretion proteins in B. bronchiseptica, Yersinia and Pseudomonas. These ORFs were arranged in two putative operons, which together we have designated as the BpeI locus. The first spans nucleotides 23385–7888 and encodes the putative proteins LcrH1, BopD, BopB, LcfH2, BscI, BscJ, BscK, BscL, BscN, BscO, BscQ, BscR, BscS, BscT, BscU, and BscC, in this order. The second spans nucleotides 23580–29863 and encodes the putative proteins LcrE, LcrD, BscD and BscF, in this order. The homology of these proteins to type III secretory proteins was B. bronchiseptica (73–99%),Yersinia spp. (17–65%), Pseudomonas spp. (18–64%). The B. pertussis proteins were similar to their homologues in B. bronchiseptica, Yersinia and Pseudomonas in terms of length, molecular weight and isoelectric point. Coiled-coil domains were detected in putative translocation proteins, BopB and BopD. BopB and BopD were similar to each other, to the RTX toxin family and to cyaA, cyaB, cyaD and cyaE. The percentage G+C content of the sequence analysed was 66.16%, which is similar to the published percentage G+C (67–70%) for the B. pertussis chromosome.