A Selenium-Dependent Xanthine Dehydrogenase Triggers Biofilm Proliferation inEnterococcus faecalisthrough Oxidant Production

Abstract

Selenium has been shown to be present as a labile cofactor in a small class of molybdenum hydroxylase enzymes in several species of clostridia that specialize in the fermentation of purines and pyrimidines. This labile cofactor is poorly understood, yet recent bioinformatic studies have suggested that Enterococcus faecalis could serve as a model system to better understand the way in which this enzyme cofactor is built and the role of these metalloenzymes in the physiology of the organism. An mRNA that encodes a predicted seleniumdependent molybdenum hydroxylase (SDMH) has also been shown to be specifically increased during the transition from planktonic growth to biofilm growth. Based on these studies, we examined whether this organism produces an SDMH and probed whether selenoproteins may play a role in biofilm physiology. We observed a substantial increase in biofilm density upon the addition of uric acid to cells grown in a defined culture medium, but only when molybdate (Mo) and selenite (Se) were also added. We also observed a significant increase in biofilm density in cells cultured in tryptic soy broth with 1% glucose (TSBG) when selenite was added. In-frame deletion of selD, which encodes selenophosphate synthetase, also blocked biofilm formation that occurred upon addition of selenium. Moreover, mutation in the gene encoding the molybdoenzyme (xdh) prevented the induction of biofilm proliferation upon supplementation with selenium. Tungstate or auranofin addition also blocked this enhanced biofilm density, likely through inhibition of molybdenum or selenium cofactor synthesis. A large protein complex labeled with 75 Se is present in higher concentrations in biofilms than in planktonic cells, and the same complex is formed in TSBG. Xanthine dehydrogenase activity correlates with the presence of this labile selenoprotein complex and is absent in a selD or an xdh mutant. Enhanced biofilm density correlates strongly with higher levels of extracellular peroxide, which is produced upon the addition of selenite to TSBG. Peroxide levels are not increased in either the selD or the xdh mutant upon addition of selenite. Extracellular superoxide production, a phenomenon well established to be linked to clinical isolates, is abolished in both mutant strains. Taken together, these data provide evidence that an SDMH is involved in biofilm formation in Enterococcus faecalis, contributing to oxidant production either directly or alternatively through its involvement in redox-dependent processes linked to oxidant production.

Selenium effects on the metabolism of a Se-metabolizingLactobacillus reuteri: analysis of envelope-enriched and extracellular proteomes

“…In other anaerobic and facultative microorganisms, other genes, probably involved in Se metabolism and Mo cofactor synthesis, co-localize with this group. This specific cluster is present in a lactic acid bacterium, Enterococcus faecalis, 37 suggesting the possibility that the same scenario can occur in other LABs, such as L. reuteri. MoeA up-regulation is therefore probably linked to the expression in L. reuteri Lb2 BM of Se-dependent molybdenum hydroxylases, even if no SDMH has been identified in this study.…”

“…These enzymes are present in species also carrying the SelD protein (specifically involved in the production of selenophosphate, the activated form of Se), suggesting its involvement in the activation of Se for SDMH maturation. 36 In a study by Srivastava and coworkers, 37 an eubacterial gene cluster that links selD with a gene encoding a molybdenum hydroxylase has been described. In other anaerobic and facultative microorganisms, other genes, probably involved in Se metabolism and Mo cofactor synthesis, co-localize with this group.…”

Antioxidant and hepatoprotective role of selenium against silver nanoparticles

“…54 Also, AgNPs caused inconsistent reductions in the levels of GSH-Px in serum and tissues, perhaps because the nanoparticles have an affinity for thiol groups. 55 The alterations in the levels of these enzymes may represent an adaptive mechanism to offset the stress of exposure. Earlier studies have shown that exposure of rats to AgNPs can alter biochemical processes and AgNPs can sequester and accumulate in vital organs, including the kidney, lung, testes, and brain.…”

Tracing the Enterococci from Paleozoic Origins to the Hospital

“…S4BC). Relevant to pathogenesis, uric acid metabolism was recently shown to enhance biofilm formation by E. faecalis , requiring a selenium-dependent molybdoenzyme, xanthine dehydrogenase (EF2570) and a selenophosphate synthetase, selD (EF2567) for this activity (Srivastava et al, 2011). To identify genes involved in this pathway, and determine when they were gained, we constructed (Fig.…”