Abstract
BackgroundThioredoxin (TRX) is a powerful disulfide oxido-reductase that catalyzes a wide spectrum of redox reactions in the cell. The aim of this study is to elucidate the role of the TRX system in the oxidative stress response in Lactobacillus plantarum WCFS1.ResultsWe have identified the trxB1-encoded thioredoxin reductase (TR) as a key enzyme in the oxidative stress response of Lactobacillus plantarum WCFS1.Overexpression of the trxB1 gene resulted in a 3-fold higher TR activity in comparison to the wild-type strain. Subsequently, higher TR activity was associated with an increased resistance towards oxidative stress. We further determined the global transcriptional response to hydrogen peroxide stress in the trxB1-overexpression and wild-type strains grown in continuous cultures. Hydrogen peroxide stress and overproduction of TR collectively resulted in the up-regulation of 267 genes. Additionally, gene expression profiling showed significant differential expression of 27 genes in the trxB1-overexpression strain. Over expression of trxB1 was found to activate genes associated with DNA repair and stress mechanisms as well as genes associated with the activity of biosynthetic pathways for purine and sulfur-containing amino acids. A total of 16 genes showed a response to both TR overproduction and hydrogen peroxide stress. These genes are involved in the purine metabolism, energy metabolism (gapB) as well as in stress-response (groEL, npr2), and manganese transport (mntH2).ConclusionBased on our findings we propose that overproduction of the trxB1-encoded TR in L. plantarum improves tolerance towards oxidative stress. This response coincides with simultaneous induction of a group of 16 transcripts of genes. Within this group of genes, most are associated with oxidative stress response. The obtained crossover between datasets may explain the phenotype of the trxB1-overexpression strain, which appears to be prepared for encountering oxidative stress. This latter property can be used for engineering robustness towards oxidative stress in industrial strains of L. plantarum.
Highlights
Thioredoxin (TRX) is a powerful disulfide oxido-reductase that catalyzes a wide spectrum of redox reactions in the cell
Bioinformatics tools were used to investigate the evolutionary relationship of the TRX genes in L. plantarum WCFS1
By phylogeny analysis it was determined that the trxB2- encoding protein of L. plantarum WFCS1 is orthologous to the B. subtilis protein YUMC suggesting that these two sequences have the same molecular function namely to act as a ferredoxin NAD(P) reductase [12]
Summary
Thioredoxin (TRX) is a powerful disulfide oxido-reductase that catalyzes a wide spectrum of redox reactions in the cell. The catalytic activity of these oxido-reductases can be attributed to the -CXXC- motif found in these proteins At this cysteinerich site electrons are transferred from the reduced TRX towards the substrate (proteins, disulfides, etc). Gene expression studies in E. coli elucidated that under hydrogen peroxide stress, OxyR (transcription regulator activated by hydrogen peroxide in the cell) exerts transcription regulation on the TRX system [3]. The in-vivo TRXinteracting proteins in Saccaromyces cerevisiae were identified using yeast two-hybrid systems [7] Both proteomic approaches revealed possible associations within the complex networks of redox regulation in microorganisms and TRX and underlines the broad impact of the TRX system in the metabolic and regulatory network of the cell
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