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A second cytadhesin-like protein, MGC2, was identified in the avian respiratory pathogen Mycoplasma gallisepticum. The 912-nucleotide mgc2 gene encodes a 32.6-kDa protein with 40.9 and 31.4% identity with the M. pneumoniae P30 and M. genitalium P32 cytadhesins, respectively. Functional studies with reverse transcription-PCR, immunoblotting, double-sided immunogold labeling, and attachment inhibition assays demonstrated homology to the human mycoplasmal P30 and P32 cytadhesins. These findings suggest that there is a family of cytadhesin genes conserved among pathogenic mycoplasmas infecting widely divergent hosts.

A 150-kDa cytadhesin-like protein from Mycoplasma gallisepticum has been identified. A previously described 583-bp fragment (J.E. Dohms, L.L. Hnatow, P. Whetzel, R. Morgan and C.L. Keeler, Jr., Avian Dis. 37:380-388, 1993) was used to probe a genomic library of M. gallisepticum DNA. An 8.0-kb SacI fragment was identified, cloned, and partially sequenced. Analysis of the resulting 3,750-bp sequence revealed the presence of a 3,366-nucleotide open reading frame, mgc1. The 1,122-amino-acid protein encoded by this open reading frame, MGC1, has characteristics of a class I membrane protein and has homology with the MgPa cytadhesin of Mycoplasma genitalium (26.3%) and the P1 cytadhesin of Mycoplasma pneumoniae (28.7%). A portion of MGC1 was expressed as a glutathione S-transferase fusion protein and used to produce antiserum in rabbits. The antiserum recognizes a 150-kDa protein from M. gallisepticum. The protein is sensitive to trypsin, confirming that it is surface exposed. Primer extension analysis indicates that the mgc1 RNA starts within an upstream open reading frame, suggesting complex control of its expression. This is the first description of a functional gene from M. gallisepticum showing homology to cytadhesin genes from human mycoplasmas.

A portion of the putative Mycoplasma gallisepticum (MG) cytadhesin gene was identified and used as a diagnostic DNA probe. Degenerate oligonucleotide primers corresponding to conserved regions of the cytadhesin proteins from two human mycoplasmas, M. pneumoniae and M. genitalium, were synthesized for use in the polymerase chain reaction (PCR) on genomic MG DNA. A 583-base-pair MG DNA fragment was amplified and subsequently cloned and sequenced. The MG DNA fragment is predicted to encode a 193-amino-acid peptide. This peptide demonstrates significant homology to the expected portions of the two human mycoplasmal cytadhesin proteins. Used as a probe to study the distribution of this fragment in pathogenic and nonpathogenic avian mycoplasmas, the PCR product hybridized to genomic DNA from all seven MG strains tested. However, it failed to hybridize to M. synoviae, M. meleagridis, M. iowae, or M. gallinarum DNA.