faecalis is grown under respiration-permissive conditions, that is, in the presence of heme. Glycerol can be metabolized by E. faecalis via two different pathways (Jacobs & Vandemark, 1960; Bizzini et al., 2010). One of them,

which is predominant in strain OG1RF, comprises Ixazomib the enzyme glycerol-3-phosphate oxidase (GlpO) that oxidizes glycerol-3-phosphate to dihydroxyacetone phosphate and reduces molecular oxygen to hydrogen peroxide. It was shown previously that an E. faecalis Npr-defective mutant grows poorly on media containing glycerol as carbon source due to accumulation of hydrogen peroxide in the cell (La Carbona et al., 2007). The npr transposon-insertion mutant EMB15 used in this study showed the same phenotype when grown on TSB agar plates supplemented with 0.3% glycerol. Supplementation of the medium with 8 μM hemin allowed normal growth of strain EMB15 also in the presence of glycerol. To investigate the role of catalase in resistance buy Protease Inhibitor Library to endogenous hydrogen peroxide stress, we grew E. faecalis strains OG1RF and EMB15 in TSB with and without hemin added until mid-exponential growth phase. Then, glycerol was added and the incubation was continued. Shortly after glycerol

addition, the Npr-defective mutant, but not the wild type, stopped growing in medium without hemin. In contrast, only little difference in growth between these strains was seen in heme-supplemented medium (Fig. 4). These results show that heme supplementation can complement Npr deficiency. Catalase-mutant EMB2 grown in medium with and without heme behaved like the wild-type strain OG1RF in this type of experiment (data not shown) which emphasize the role of Npr in resistance to endogenous hydrogen peroxide stress. In this study, we show that catalase in E. faecalis plays a partially protective role against toxic effects of externally added hydrogen peroxide. Histone demethylase Suppression of the glycerol-sensitive phenotype of an Npr-deficient mutant by heme supplementation of the growth medium indicates that catalase also protects against endogenous hydrogen peroxide stress. Although heme is found in many environments (Lechardeur et al., 2011), its availability is often limited, for

example, in animal tissues by binding to specialized heme-binding proteins. Most pathogenic bacteria have evolved mechanisms to acquire heme from host proteins (Anzaldi & Skaar, 2010). No heme uptake system has yet been identified in E. faecalis, and the mechanism of how this bacterium obtains heme for catalase biogenesis from the environment is not known. Interestingly, no homolog of katA, encoding the catalase protein, can be found in the available genomes of other Enterococcus species, nor in the phylogenetically closely related Lactococci and Streptococci. Thus, E. faecalis apparently harbors catalase as an extra layer of protection against oxidative stress under conditions where heme is available. This work was supported by grant 621-2010-5672 from the Swedish Research Council.