A haem receptor gene fromPhotobacterium damselaesubsp.piscicida(formerly known asPasteurella piscicida) has been cloned, sequenced and analysed for its function. The gene, designated aspph, has an open reading frame consisting of 2154 bp, a predicted 718 amino acid residues and exists as a single copy. It is homologous with the haem receptors ofVibrio anguillarum hupA,V. cholerae hutA,V. mimicus mhuAandV. vulnificus hupAat 32.7, 32.7, 45.6 and 30.9%, respectively, and is highly conserved, consisting of a Phe-Arg-Ala-Pro sequence (FRAP), an iron transport related molecule (TonB) and a Asn-Pron-Asn-Leu sequence (NPNL), binding motifs associated with haem receptors. As a single gene knockout mutantP. damselaesubsp.piscicidawas able to bind haem in the absence ofpph, suggesting that other receptors may be involved in its iron transport system. This study shows that theP. damselaesubsp.piscicida pphbelongs to the haem receptor family, is conserved and that its iron-binding system may involve more than one receptor. [ABSTRACT FROM AUTHOR]