Abstract
The Firmicutes bacteria participate extensively in virulence and pathological processes. Enterococcus faecalis is a commensal microorganism; however, it is also a pathogenic bacterium mainly associated with nosocomial infections in immunocompromised patients. Iron-sulfur [Fe-S] clusters are inorganic prosthetic groups involved in diverse biological processes, whose in vivo formation requires several specific protein machineries. Escherichia coli is one of the most frequently studied microorganisms regarding [Fe-S] cluster biogenesis and encodes the iron-sulfur cluster and sulfur assimilation systems. In Firmicutes species, a unique operon composed of the sufCDSUB genes is responsible for [Fe-S] cluster biogenesis. The aim of this study was to investigate the potential of the E. faecalis sufCDSUB system in the [Fe-S] cluster assembly using oxidative stress and iron depletion as adverse growth conditions. Quantitative real-time polymerase chain reaction demonstrated, for the first time, that Gram-positive bacteria possess an OxyR component responsive to oxidative stress conditions, as fully described for E. coli models. Likewise, strong expression of the sufCDSUB genes was observed in low concentrations of hydrogen peroxide, indicating that the lowest concentration of oxygen free radicals inside cells, known to be highly damaging to [Fe-S] clusters, is sufficient to trigger the transcriptional machinery for prompt replacement of [Fe-S] clusters.
Highlights
Iron-sulfur ([Fe-S]) clusters are ubiquitous inorganic prosthetic groups involved in biological processes as diverse as electron transfer, redox and non-redox catalysis and gene regulation (Frazzon & Dean 2003, Lill 2009)
These values were statistically significant when compared to the control group and indicated a substantial transcriptional increase of these genes, as illustrated by relative gene expression (2-∆∆critical threshold (Ct)) in the heat-map shown in Fig. 4. kat, a gene whose expression pattern is indicative of oxidative stress, was included in the experiment as a positive control to indicate this growth challenge
This paper describes the transcriptional pattern of genes related to the [Fe-S] cluster assembly in E. faecalis cells under oxidative stress and iron depletion conditions
Summary
Iron-sulfur ([Fe-S]) clusters are ubiquitous inorganic prosthetic groups involved in biological processes as diverse as electron transfer, redox and non-redox catalysis and gene regulation (Frazzon & Dean 2003, Lill 2009). [Fe-S] cluster assembly and delivery are most frequently studied in Proteobacteria, for which three types of biosynthetic machineries have been described: nitrogen fixation (NIF), iron-sulfur cluster (ISC) and sulfur assimilation (SUF). The demonstration of complementation in trans of E. coli sufABCDSE by the E. faecalis sufCDSUB suggested a degree of similarity between these machineries (Riboldi et al 2011). Considering the high degree of conservation of the SUF system in Firmicutes, the sole presence of the sufCDSUB operon in E. faecalis and the fact that iron depletion and cellular oxidative stress are linked to the regulation of the SUF machinery in well-characterised organisms, the aim of this study was to investigate the potential of the E. faecalis sufCDSUB system in [Fe-S] cluster assembly, using oxidative stress and iron depletion as adverse growing conditions
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