Abstract
BackgroundSecDF is an accessory factor of the conserved Sec protein translocation machinery and belongs to the resistance-nodulation-cell division (RND) family of multidrug exporters. SecDF has been shown in Escherichia coli and Bacillus subtilis to be involved in the export of proteins. RND proteins can mediate resistance against various substances and might be of relevance in antimicrobial therapy. The role of RND proteins in Staphylococcus aureus has not yet been determined.ResultsMarkerless deletion mutants were constructed to analyze the impact of the so far uncharacterized RND proteins in S. aureus. While the lack of Sa2056 and Sa2339 caused no phenotype regarding growth and resistance, the secDF mutant resulted in a pleiotropic phenotype. The secDF mutant was cold sensitive, but grew normally in rich medium at 37°C. Resistance to beta-lactams, glycopeptides and the RND substrates acriflavine, ethidium bromide and sodium dodecyl sulfate was reduced. The secDF mutant showed an aberrant cell separation and increased spontaneous and Triton X-100 induced autolysis, although the amounts of penicillin-binding proteins in the membrane were unchanged. The impact of secDF deletion on transcription and expression of specific virulence determinants varied: While coagulase transcription and activity were reduced, the opposite was observed for the autolysin Atl. A reduction of the transcription of the cell wall anchored protein A (spa) was also found. The accumulation of SpA in the membrane and lowered amounts in the cell wall pointed to an impaired translocation.ConclusionsThe combination of different effects of secDF deletion on transcription, regulation and translocation lead to impaired cell division, reduced resistance and altered expression of virulence determinants suggesting SecDF to be of major relevance in S. aureus. Thus SecDF could be a potential target for the control and eradication of S. aureus in the future.
Highlights
SecDF is an accessory factor of the conserved Sec protein translocation machinery and belongs to the resistance-nodulation-cell division (RND) family of multidrug exporters
Deletion of sa2056 and sa2339 had no apparent effect on S. aureus when evaluating growth and resistance properties, suggesting that they may be important under other conditions than applied in this study
Transcription of secDF and growth phenotype of the secDF mutant Transcription of secDF was monitored from early exponential to early stationary phase and found to result mainly in a monocistronic mRNA. secDF was strongest transcribed during early growth phase and declined towards stationary phase (Figure 1A)
Summary
SecDF is an accessory factor of the conserved Sec protein translocation machinery and belongs to the resistance-nodulation-cell division (RND) family of multidrug exporters. Sec-mediated translocation has best been studied in Escherichia coli and is catalyzed by the essential SecYEG protein complex (reviewed in [2]). The accessory SecDF-YajC complex facilitates protein export and membrane protein insertion efficiency in vivo [3], possibly via the control of SecA cycling [4]. SecYEG has been shown to interact with the SecDF-YajC complex [8]. YidC, a protein that is proposed to mediate membrane integration and the assembly of multimeric complexes, can interact with SecDF-YajC to take over SecYEG-dependent membrane proteins [9]
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