Genomic analysis reveals RepMP1- mediated recombination in Mycoplasma pneumoniae clinical isolate

Department of Microbiology and Immunology, 7703 Floyd Curl Drive, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229-3900, USA

^* To whom correspondence should be addressed. Email: baseman{at}uthscsa.edu.

	Abstract

Mycoplasmas are cell wall-less bacteria that have evolved by drastic reduction of their genome size. Complete genome analysis of Mycoplasma pneumoniae revealed the presence of numerous copies of four distinct large repetitive elements (RepMPs). One copy of each RepMP2/3, RepMP4 and RepMP5 are localized within the P1 operon (loci MPN140 to MPN142) and their involvement in sequence variations of adhesin P1 and adherence-related protein B/C has been documented. Here we analyzed a clinical strain of M. pneumoniae designated S1 isolated from a 1993 outbreak of respiratory infections in San Antonio, Texas. Based on the type of RepMPs within the P1 operon, we classified the clinical isolate S1 as type 2 with minor unique sequence variations. Hybridization with oligonucleotide arrays revealed sequence divergence in two previously unsuspected hypothetical genes (loci MPN137 and MPN138). Closer inspection of this region revealed that loci MPN137 and MPN138 harbored previously unrecognized M. pneumoniae-unique repetitive RepMP1 sequences. PCR and sequence analyses uncovered a recombination event involving three RepMP1-containing genes that resulted in fusion of MPN137 and MPN138 reading frames and loss of all but a short fragment of another RepMP1-containing locus, MPN130. The multiple copies of M. pneumoniae unique RepMP1 repetitive elements spread throughout the chromosome could allow for vast numbers of sequence variations among clinical strains. Comparisons of amino acid sequences showed the presence of leucine zipper (LZ) motifs in MPN130 and MPN138 proteins in reference strain M129 and their loss in the fused protein of S1. The presence of tandem leucine- and other repeats points to possible regulatory functions of RepMP1-containing proteins.