Mycoplasma pneumoniae P1 type 1- and type 2-specific sequences within the P1 cytadhesin gene of individual strains

Abstract

Mycoplasma pneumoniae strains traditionally are divided into two types, based on sequence variation in the P1 gene. Recently, however, we have identified 8 P1 subtypes by restriction fragment length polymorphism analysis. In the present study the P1 gene sequences of three P1 type 1 and two P1 type 2 M. pneumoniae strains were analyzed. A new P1 gene sequence in a type 1 strain with partial similarity to a recently reported variable region in the P1 gene of an M. pneumoniae type 2 strain (T. Kenri, R. Taniguchi, Y. Sasaki, N. Okazaki, M. Narita, K. Izumikawa, M. Umetsu, and T.Sasaki, Infect. Immun. 67:4557-4562, 1999) was identified. In addition, the P1 gene of the type 1 strain contained another region with nucleotide polymorphisms identical to a stretch in the P1 gene of one of our type 2 strains. These findings indicate that recombination between sequences specific for P1 type 1 and type 2 had occurred and that P1 type 1 and type 2 hybrid sequences can be present within the P1 gene of an individual strain. Identical or nearly identical variable P1 gene sequences were present in several repetitive regions outside the P1 gene locus in the genome of M. pneumoniae strain M129, implying recombination as a mechanism for generation of the P1 gene variation. Additionally, in the P1 gene sequences of four of the five strains studied, single-nucleotide polymorphisms different from the previously reported P1 type 1 and 2 characteristic sequences were identified. The polymorphic sites are candidate targets for genotyping of M. pneumoniae by direct sequencing of amplicons from clinical specimens.

FIG. 1

Schematic representation of sequence divergence of ADH3-ADH4 amplicons (nt 2268 to 4768 relative to the start codon AUG of the P1 gene of strain M129 [29]) of the P1 genes of three P1 type 1 and three P1 type 2 M. pneumoniae strains. Sequence data for strain 309 are derived from reference . The figure is not drawn to scale.

FIG. 2

Partial P1 nucleotide sequences of strains M129 (P1 type 1) and TW 7-5 (P1 type 2) and of the variable regions in strains Mp4817 (present study) and 309 (15), corresponding to region A in Fig 1. Nucleotide positions are indicated relative to the start codon AUG of the P1 genes of strain M129 (29) and strain TW 7-5 (26). Identical nucleotides are indicated by dots, and gaps are indicated by dashes. Differing nucleotides are shown. Nucleotide differences between reference P1 type 1 and 2 strains are marked with asterisks. The variable stretch which is identical in strains Mp4817 and 309 (region B in Fig. 1) is underlined.

FIG. 3

Deduced partial amino acid sequences of P1 proteins of strains M129, TW 7-5, Mp4817, and 309. The regions shown correspond to the nucleotide sequences from nt 3571 onwards in Fig 2. Amino acid differences between reference P1 type 1 and 2 strains are marked with asterisks. The variable stretch which is identical in Mp4817 and 309 (corresponding to region B in Fig. 1) is underlined. Amino acid positions of the P1 proteins of M129 (29) and TW 7-5 (26) are indicated according to the published sequences.