pleuropneumoniae strain 4074 and R2846). However, Blast searches show that the encoded protein has significant homology to TonB-dependent outer membrane proteins of other bacterial species. TonB-dependent proteins are generally associated with the uptake of iron, heme and other small molecules [34]. Neisseria sicca, a common nasopharyngeal commensal which rarely causes infectious disease [35], encodes a TonB-dependent receptor family protein that has the highest sequence homology

to the protein encoded by r2846.1777 from H. influenzae (60% identity, 74% similarity). The next highest homology to r2846.1777 of R2846 (55% identity, 72% similarity) was Selleck HIF inhibitor associated with a ferric siderophore receptor produced by Bordetella pertussis, also a frequent colonizer of the human nasopharynx and a commonly occurring pathogen. r2846.1777 also exhibits significant amino acid identity to other uncharacterized putative TonB-dependent outer membrane proteins from a number of additional Bordetella species (B. bronchiseptica, B. avium, B. parapertussis and B. petrii), as well as Pseudomonas, Burkholderia and Nitrosomonas and Acidovorax species. These homology studies suggest that

the proteins comprising the hydroxamate siderophore ABC transport system (encoded by the fhuCDB genes of strain R2846) may be of different origin than the putative siderophore-binding protein gene encoded by r2846.1777. The H. influenzae buy C646 locus r2846.1777 may have originated from bacterial species known to colonize the human nasopharynx. Thus, r2846.1777 of NTHi strain R2846 encodes a Ton-B dependent outer

membrane protein of unknown function. Methocarbamol However, it is likely, based on its proximity to genes encoding proteins showing significant identity at the amino acid level to known siderophore associated periplasmic transport systems, that r2846.1777 encodes a siderophore-binding outer membrane binding protein. However, since the product of r2846.1777 exhibits low homology with characterized FhuA proteins and since, to date, we have been unable to construct a mutant in r2846.1777 for phenotypic analyses we will use the designation r2846.1777 in the following discussions of this putative gene and its encoded protein. The fhu gene cluster of NTHi strain R2846 is similarly arranged to those of A. pleuropneumoniae in that the putative receptor encoding gene (r2846.1777) is located downstream of fhuCDB, in contrast to the gene arrangement in E. coli where the outer membrane protein-encoding gene (fhuA) is upstream of the other three genes. The gene arrangement seen in both NTHi strain R2846 and A. pleuropneumoniae, has also been reported for a third representative of the family Pasteurellaceae, namely H. parasuis [36]. Blast searches demonstrate that the fifth gene of the gene cluster (designated orf5 in Figure 1) identified in NTHi strain R2846 exhibits significant homology to an internal fragment of a transposon integrase (data not shown).