AEROMONAS SPP. POSSESS AT LEAST 2 DISTINCT TYPE-IV PILUS FAMILIES

Type IV pill have been purified from strains of most of the Aeromonas species associated with gastroenteritis (A. veronii biovar sobria, A. hydrophila, A. trota and A. caviae). They appear to be a related famil y (molecular mass of pilin 19 to 23 kDa) with a tendency to bundle-for mation. Hence, we have designated them 'bundle-forming pili' (Bfp). A type IV pilus biogenesis gene cluster (tapABCD) recently cloned from a strain of A. hydrophila, however, encoded a 17 kDa pilin which differ ed significantly in its N-terminal amino acid sequence from the Bfp pi lins. This paper describes the cloning of part (tapA and similar to 20 % of tapB) of a homologous pilin gene cluster from a Bfp-positive stra in of A. veronii biovar sobria, and presents evidence that the entire pilin gene cluster (tapABCD) is present in this strain. The predicted N-terminal amino acid sequence of the pilin encoded by the A. veronii biovar sobria tapA differed markedly from the corresponding sequence o f its Bfp pilin, and those of the Bfp purified from other Aeromonas st rains and species. Probing with tapA and tapD genes showed that these Bfp-positive Aeromonas strains also possessed the Tap gene cluster. Ta pA proteins of A. veronii biovar sobria and A. hydrophila shared 53% i dentity and 63% homology. We conclude that Aeromonas species are poten tially able to express at least two distinct families of type IV pili (Bfp and Tap). (C) 1997 Academic Press Limited.