Submitted to: Current Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/10/2003
Publication Date: 2/25/2004
Citation: Wan, X., Branton, S.L., Hanson, L.A., Pharr, G.T. 2004. Identification and initial characterization of a putative mycoplasma gallinarum leucine aminopeptidase gene. Current Microbiology. 48:32-38. Interpretive Summary: The smallest bacteria known is Mycoplasma and birds can have as many as 25 different types. Four types have been identified which cause diseases in chickens and turkeys and results in economic losses of about $150 million dollars annually. One type, Mycoplasma gallinarum, does not cause disease at all and yet is found in not only chickens but also cattle, sheep and pigs. These facts suggesting that it may be a suitable basis for a recombinant vaccine. This research was conducted to determine whether a particular enzyme system, leucine aminopeptidase, is present in the organism. The enzyme was determined to be present and thus, may help to explain why this organism is found in so many animals. The fact that this enzyme was found to be present will be used to aid in constructing a mycoplasma vaccine for use in poultry.
Technical Abstract: Unlike most other host-specific mycoplasmas, Mycoplasma gallinarum is a commensal with a host range including most poultry as well as some mammals. This property of M. gallinarum may reflect unique mechanisms for its colonization and persistence in hosts. The aminopeptidases have been suggested to play a potential role in the host colonization by supplying nutrition from peptide degradation and amino acid scavenging. While M. gallinarum shows leucine and arginine aminopeptidase activity, the genes encoding the enzymes had not been cloned and characterized. We identified an aminopeptidase gene by oligonucleotide hybridization to a genomic library of M. gallinarum. Nucleotide sequence analysis of overlapping phage clones identified a 1,362 bp open reading frame (ORF) encoding a putative leucine aminopeptidase gene. This ORF has 68% nucleotide identity and 51% amino acid identity with the M. salivarium leucine aminopeptidase gene. The amino acid residues conserved in the active site of leucine aminopeptidases in other eukaryotes and prokaryotes were conserved in the cloned aminopeptidase gene. Northern-blot hybridization analysis showed that this ORF is expressed on a 1.5 kb monocistronic transcript. Southern-blot hybridization analysis demonstrated this gene was present as a single copy in M. gallinarum. Characterization of the leucine aminopeptidase suggests that it is a metallo-aminopeptidase that is located in the cytoplasm with a weak interaction with the cell membrane. These features suggest a potential role of this leucine aminopeptidase in the nutritional supply of M. gallinarum.