Cross-complementation between the products of the genes P1 and ORF6 of Mycoplasma pneumoniae subtypes 1 and 2

Abstract

The genes P1 (MPN141) and ORF6 (MPN142) are essential for the successful colonization of the human respiratory tract by Mycoplasma pneumoniae. Both genes are located in the P1 operon, which consists of three genes. The P1 gene is the second gene in the operon, followed by the ORF6 gene. The P1 gene contains two (RepMP2/3, RepMP4) and the ORF6 gene one (RepMP5) specific repetitive DNA sequence, of which seven to nine similar but not identical copies are dispersed on the genome. Despite this large potential pool for genetic variation, M. pneumoniae isolates from patients contain only one of two distinct combinations of the genes P1 and ORF6. To analyse the functions of the repetitive DNA sequences, two 'new' combinations of the genes P1 and ORF6 were constructed, keeping the P1 gene constant but exchanging RepMP5 copies of the ORF6 gene. M. pneumoniae was transformed with these constructs and the transformants were tested for their ability to grow and survive under in vitro conditions and in guinea pigs. The two transformants colonized the respiratory tract of guinea pigs and showed no obvious differences in their growth behaviour compared to M. pneumoniae isolates from patients. The results indicate that the subtype-specific combinations of the repetitive elements in the P1 and ORF6 genes are not essential for the successful adherence of M. pneumoniae to host cells and the colonization of the respiratory tract of guinea pigs.