Comparative proteomics of two <i>Mycoplasma hyopneumoniae</i> strains and <i>Mycoplasma flocculare</i> identified potential porcine enzootic pneumonia determinants

<i>Mycoplasma hyopneumoniae</i> and <i>Mycoplasma flocculare</i> are genetically similar bacteria, which coinhabit the porcine respiratory tract. These mycoplasmas share most of the known virulence factors, but, while <i>M. hyopneumoniae</i> causes porcine enzootic pneumonia (PEP), <i>M. flocculare</i> is a commensal species. To identify potential PEP determinants and provide novel insights on mycoplasma-host interactions, the whole cell proteomes of two <i>M. hyopneumoniae</i> strains, one pathogenic (7448) and other non-pathogenic (J), and <i>M. flocculare</i> were compared. A cell fractioning approach combined with mass spectrometry (LC-MS/MS) proteomics was used to analyze cytoplasmic and surface-enriched protein fractions. Average detection of ~ 50% of the predicted proteomes of <i>M. hyopneumoniae</i> 7448 and J, and <i>M. flocculare</i> was achieved. Many of the identified proteins were differentially represented in <i>M. hyopneumoniae</i> 7448 in comparison to <i>M. hyopneumoniae</i> J and <i>M. flocculare</i>, including potential PEP determinants, such as adhesins, proteases, and redox-balancing proteins, among others. The LC-MS/MS data also provided experimental validation for several genes previously regarded as hypothetical for all analyzed mycoplasmas, including some coding for proteins bearing virulence-related functional domains. The comprehensive proteome profiling of two <i>M. hyopneumoniae</i> strains and <i>M. flocculare</i> provided tens of novel candidates to PEP determinants or virulence factors, beyond those classically described.