A gene family in Mycoplasma imitans closely related to the pMGA family of Mycoplasma gallisepticum

The avian pathogen Mycoplasma gallisepticum possesses a large gene family encoding lipoproteins which function as haemagglutinins. Representative species of the pneumoniae phylogenetic group of mycoplasmas were examined for the presence of genes homologous to members of this multigene family. Antisera against the pMGA1.1 lipoprotein recognized a 35 kDa protein in Mycoplasma imitans, but did not recognize proteins of Mycoplasma genitalium, Mycoplasma pneumoniae, Mycoplasma pirum, Mycoplasma penetrans or Mycoplasma iowae in Western blots. A fragment of the pMGA1.2 gene and oligonucleotide probes complementary to highly conserved coding and non-coding regions of pMGA genes bound to fragments of genomic DNA of M. imitans, but not to the genomes of M. genitalium, M. pneumoniae, M. pirum or M. penetrans, and only one probe bound to a fragment of the M. iowae genome. One homologue of the pMGA genes was amplified from the M. imitans genome by PCR and used as a probe to clone a 3.1 kbp DNA fragment from a library of HindIII-digested M. imitans genomic DNA. The contiguous DNA sequence of the PCR and HindIII clones was predicted to encode one complete and one partial ORF which shared some peptide sequence identity with the pMGA genes, including the signal peptidase II cleavage site and the proline-rich amino-terminal region. Like the pMGA genes, the M. imitans genes were found to be members of a large gene family, with an association with GAA trinucleotide repeats, a feature which distinguishes these two families from the homologous vlhA gene family in Mycoplasma synoviae. The identification of these gene families in three phylogenetically distinct avian mycoplasma species, but not in human mycoplasmas, suggests their horizontal transfer between species infecting the same host.