Characterization of pMGA Genes from the F - Strain (Vaccine Strain)

Our long term goal is to determine the role that pMGA hemagglutinins play in Mycoplasma gallisepticum F-strain (termed as F-strain for brevity) persistence in poultry. To do this however, we first had to identify the pMGA genes expressed by an isolate of the F-strain. To identify F-strain pMGA genes, a genomic library was constructed in bacteriophage lambda and screened with polyclonal antisera raised against F-strain surface antigens capable of inhibiting agglutination of chicken red blood cells. One phage clone was identified, designated 8 9, which remained positive through additional rounds of screening and was sequenced. Sequence data analysis predicted one complete and two partial open reading frames (ORF) arranged in tandem within the 4.5 kb genomic insert, termed ORF 9.1, ORF 9.2 and ORF 9.3, which showed significant homology to the pMGA gene family of M. gallisepticum. The number of GAA trinucleotide repeats in the intergenic region of 9.3 ORF suggested that this ORF is expressed. The pMGA cDNAs amplified from the F-strain showed significant homology to the 9.3 ORF. One set of cDNAs however, differed from the 9.3 ORF sequence by a repeat of the sequence “AACCAAA” in the 5' end. We conclude that the F-strain vaccine isolate expresses pMGA gene variants, similar to what has been described in field strains of M. gallisepticum.