Comparative analysis of pathogenic and nonpathogenic Mollicutes. Mollicutes

Comparative genomic analysis of 3 new Mycoplasma genomes and 9 previously published genomes revealed strain-specific sequences that may be related to pathogenicity. Strain 7448 contained a conjugative element (ICEH - integrated conjugative element of Mycoplasma hyopneumoniae) similar to ICEF of Mycoplasma fermentans and it was found to produce a circular extrachromosomal element in some isolates. A comparison of the pathogenic strains (7448 and 232) with the nonpathogenic strain (J) revealed some key differences in the coding regions of a number of adhesins and putative adhesins, mostly in the number of repetitive amino acid sequences found in each coding region. Since all 3 strains encode the adhesins that have been found to be important for Mycoplasma hyopneumoniae pathogenicity, these differents in repetitive sequences must be important in the adhesion differences reported for these three strains. A few potential horizontal transfer (HGT) events were detected when comparing Mycoplasma synoviae and Mycoplasma gallisepticum. Fourteen putative HGT regions were detected, one of which contained a sialidase that presumably cleaves terminal sialic acid residues from host glycoproteins. Mycoplasma synoviae encodes a number of sialic acid catabolic genes so cleavage of terminal sialic acid residues may serve as a nutrient source for this organism. Another HGT event regarding pathogenicity was discovered when it was found that three hemagglutinin coding regions were likely transferred from M. gallisepticum to M. synoviae. Further genomic comparison revealed a minimal set of metabolic capabilities being retained in all genomes instead of specific genes or pathways. A minimal set of cytadhesins that are involved in tip organelle formation were also conserved in all genomes, while accessory proteins and other components were not conserved, suggesting that many aspects of cellular adhesion have undergone rapid evolution.