Role of <i>mutS</i> and <i>mutL</i> Genes in Hypermutability and Recombination in <i>Staphylococcus aureus</i>

<jats:title>ABSTRACT</jats:title> <jats:p> The mutator phenotype has been linked in several bacterial genera to a defect in the methyl-mismatch repair system, in which the major components are MutS and MutL. This system is involved both in mismatch repair and in prevention of recombination between homeologous fragments in <jats:italic>Escherichia coli</jats:italic> and has been shown to play an important role in the adaptation of bacterial populations in changing and stressful environments. In this report we describe the molecular analysis of the <jats:italic>mutS</jats:italic> and <jats:italic>mutL</jats:italic> genes of <jats:italic>Staphylococcus aureus</jats:italic> . A genetic analysis of the <jats:italic>mutSL</jats:italic> region was performed in <jats:italic>S. aureus</jats:italic> RN4220. Reverse transcriptase PCR experiments confirmed the operon structure already reported in other gram-positive organisms. Insertional inactivation of <jats:italic>mutS</jats:italic> and <jats:italic>mutL</jats:italic> genes and complementation showed the role of both genes in hypermutability in this species. We also designed an in vitro model to study the role of MutS and MutL in homeologous recombination in <jats:italic>S. aureus</jats:italic> . For this purpose, we constructed a bank of <jats:italic>S. aureus</jats:italic> RN4220 and <jats:italic>mutS</jats:italic> and <jats:italic>mutL</jats:italic> mutants containing the integrative thermosensitive vector pBT1 in which fragments with various levels of identity (74% to 100%) to the <jats:italic>S. aureus sodA</jats:italic> gene were cloned. MutS and MutL proteins seemed to have a limited effect on the control of homeologous recombination. Sequence of <jats:italic>mutS</jats:italic> and <jats:italic>mutL</jats:italic> genes was analyzed in 11 hypermutable <jats:italic>S. aureus</jats:italic> clinical isolates. In four of five isolates with mutated or deleted <jats:italic>mutS</jats:italic> or <jats:italic>mutL</jats:italic> genes, a relationship between alterations and mutator phenotypes could be established by negative complementation of the <jats:italic>mutS</jats:italic> or <jats:italic>mutL</jats:italic> mutants. </jats:p>