Role of N-terminal protein formylation in central metabolic processes in Staphylococcus aureus

Background: Bacterial protein biosynthesis usually depends on a formylated methionyl start tRNA but Staphylococcus aureus is viable in the absence of Fmt, the tRNA(Met) formyl transferase. fmt mutants exhibit reduced growth rates indicating that the function of certain proteins depends on formylated N-termini but it has remained unclear, which cellular processes are abrogated by the lack of formylation. Results: In order to elucidate how global metabolic processes are affected by the absence of formylated proteins the exometabolome of an S. aureus fmt mutant was compared with that of the parental strain and the transcription of corresponding enzymes was analyzed to identify possible regulatory changes. The mutant consumed glucose and other carbon sources slower than the wild type. While the turnover of several metabolites remained unaltered fmt inactivation led to increases pyruvate release and, concomitantly, reduced pyruvate dehydrogenase activity. In parallel, the release of the pyruvate-derived metabolites lactate, acetoin, and alanine was reduced. The anaerobic degradation of arginine was also reduced in the fmt mutant compared to the wild-type strain. Moreover, the lack of formylated proteins caused increased susceptibility to the antibiotics trimethoprim and sulamethoxazole suggesting that folic acid-dependant pathways were perturbed in the mutant. Conclusions: These data indicate that formylated proteins are crucial for specific bacterial metabolic processes and they may help to understand why it has remained important during bacterial evolution to initiate protein biosynthesis with a formylated tRNA(Met).