Survival strategies of Clostridium difficile to fluctuating concentrations of oxygen

Oxygen and reactive oxygen species (ROS) can react with multiple cellular components, leading to the inactivation of a plethora of metabolic pathways. Therefore, organisms have systems to sense and eliminate O2 and ROS, contributing to their survival in the adverse host environment.

Clostridium difficile P28 is an anaerobic pathogenic bacterium that contains in its genome a flavodiiron protein (FDP) and a rubrerythrin (Rbr), that are putatively involved in the detoxification pathways used by this organism.

Flavodiiron proteins are widespread in all life domains, with a crucial role in O2 detoxification, through its reduction directly to water. FDPs are cytoplasmic enzymes with a minimal structural unit composed by two main domains, a metallo-β-lactamase domain, containing the catalytic diiron site, and a flavodoxin domain having a flavin mononucleotide. Rubrerythrins are generally considered to act as NADH-linked hydrogen peroxide reductases, thus eliminating this ROS, and are composed by two iron sites: a diiron center and a rubredoxin-like FeCys4 center.

In this work with characterized biochemically, spectroscopically, structurally and kinetically the FDP and Rbr and their two putative redox partners, a High Molecular Weight Rubredoxin (HRb) and a Rubredoxin (Rd). We confirmed the existence of direct electron transfer between HRb, Rd and FDP and also between HRb, Rd and Rbr. In addition, we also established the reaction rates for the reduction, by FDP, of O2(0.43s-1) and H2O2 (0.06s-1) and for the reduction of H2O2by Rbr (1.53s-1). The enzymatic activity of Rbr towards O2 was also investigated.

Romão, C.V., et al, 2016.JBIC., 21:39-52.

Martins, M.C., et al., 2019. FRBM, in press.