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 e ncoding lipoproteins which function as haemagglutinins. Representative spec ies of the pneumoniae phylogenetic group of mycoplasmas were examined for t he presence of genes homologous to members of this multigene family. Antise ra against the pMGA1.1 lipoprotein recognized a 35 kDa protein in Mycoplasm a imitans, but did not recognize proteins of Mycoplasma genitalium, Mycopla sma 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 ge nes bound to fragments of genomic DMA of M. imitans, but not to the genomes of M. genitalium, M, pneumoniae, M, pirum or M, penetrans, and only one pr obe bound to a fragment of the M. iowae genome. One homologue of the pMGA g enes 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 pep tide 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 disti nguishes these two families from the homologous vlhA gene family in Mycopla sma synoviae. The identification of these gene families in three phylogenet ically distinct avian mycoplasma species, but not in human mycoplasmas, sug gests their horizontal transfer between species infecting the same host.