Construction and analysis of M. smegmatis mutant for a PE coding gene

M. tuberculosis, the etiological agent of human tuberculosis, is the major human pathogen causing 3 million death per year. One of the major surprises of its genome sequence was that almost 10% of its coding capacity is devoted to the production of PE and PPE proteins (1). These proteins are so named for conserved proline and glutamate residues near their N-termini. In addition to these motifs, the family members share homologous N-terminal domains of approximately 110 amino acids for PE proteins and 180 amino acids for PPE proteins. These proteins are conserved among pathogenic and non pathogenic mycobacteria but their function still remain to be addressed (2). The fast growing M. smegmatis commonly used as model system, shares many features with its slow-growing pathogenic counterpart M. tuberculosis. In particular, the analysis of M. smegmatis genome revealed the presence of a PE coding gene, Msmeg-0412, conserved in M. tuberculosis with 46% identity at amino acid level. In order to characterize this gene we constructed a M. smegmatis mutant in the PE coding gene. Preliminary experiments show that this M. smegmatis mutant is unable to form organized biofilm in vitro and is more sensitive to the action of two antibiotics, erythromycin and chloramphenicol, with respect to the wild type strain, suggesting a role of M. smegmatis PE protein in the stability of the cell-wall. Complementation experiment, using the wild type copy of the PE coding gene, is in progress to assess if the mutant phenotype observed is a direct effect of PE deficiency.