Modulation of detoxification enzymes by watercress: in vitro and in vivo investigations in human peripheral blood cells

Epidemiological studies indicate that consumption of cruciferous vegetables (CV) can reduce the risk of cancer. Supposed mechanisms are partly the inhibition of phase I and the induction of phase II enzymes. The aim of this study was to investigate in vitro and in vivo effects of watercress (WC), a member of the CV family, on chemopreventive parameters using human peripheral blood mononuclear cells (PBMC) as surrogate cells. We investigated the hypothesis that WC reduces cancer risk by inducing detoxification enzymes in a genotype-dependent manner. In vitro gene expression and enzyme activity experiments used PBMC incubated with a crude extract from fresh watercress (WCE, 0.1-10 mu L/mL with 8.2 g WC per 1 mL extract) or with one main key compound phenethyl isothiocyanate (PEITC, 1-10 mu M). From an in vivo perspective, gene expression and glutathione S-transferase (GST) polymorphisms were determined in PBMC obtained from a human intervention study in which subjects consumed 85 g WC per day for 8 weeks. The influence of WC consumption on gene expression was determined for detoxification enzymes such as superoxide dismutase 2 (SOD2) and glutathione peroxidase 1 (GPX1), whilst the SOD and GPX activities in red blood cells were also analysed with respect to GST genotypes. In vitro exposure of PBMC to WCE or PEITC (24 h) increased gene expression for both detoxification enzymes GPX1 (5.5-fold, 1 mu L/mL WCE, 3.7-fold 1 mu M PEITC) and SOD2 (12.1-fold, 10 mu L/mL WCE, 7.3-fold, 10 mu M PEITC), and increased SOD2 activity (1.9-fold, 10 mu L/mL WCE). The WC intervention had no significant effect on in vivo PBMC gene expression, as high individual variations were observed. However, a small but significant increase in GPX (p = 0.025) and SOD enzyme activity (p = 0.054) in red blood cells was observed in GSTM1*0, but not in GSTM1*1 individuals, whilst the GSTT1 genotype had no impact. The results indicate that WC is able to modulate the enzymes SOD and GPX in blood cells in vitro and in vivo, and suggest that the capacity of moderate intake of CV to induce detoxification is dependent in part on the GSTM1 genotype.

Sulforaphane protects cortical neurons against 5-S-cysteinyl-dopamine-induced toxicity through the activation of ERK1/2, Nrf-2 and the upregulation of detoxification enzymes

The degeneration of dopaminergic neurons in the substantia nigra has been linked to the formation of the endogenous neurotoxin 5-S-cysteinyl-dopamine. Sulforaphane (SFN), an isothiocyanate derived from the corresponding precursor glucosinolate found in cruciferous vegetables has been observed to exert a range of biological activities in various cell populations. In this study, we show that SFN protects primary cortical neurons against 5-S-cysteinyl-dopamine induced neuronal injury. Pre-treatment of cortical neurons with SFN (0.01-1 microM) resulted in protection against 5-S-cysteinyl-dopamine-induced neurotoxicity, which peaked at 100 nM. This protection was observed to be mediated by the ability of SFN to modulate the extracellular signal-regulated kinase 1 and 2 and the activation of Kelch-like ECH-associated protein 1/NF-E2-related factor-2 leading to the increased expression and activity of glutathione-S-transferase (M1, M3 and M5), glutathione reductase, thioredoxin reductase and NAD(P)H oxidoreductase 1. These data suggest that SFN stimulates the NF-E2-related factor-2 pathway of antioxidant gene expression in neurons and may protect against neuronal injury relevant to the aetiology of Parkinson's disease.

Phenotypic expression of homozygous hemoglobin S in relation to β-globin haplotypes, glutathione S-transferase polymorphisms and detoxification enzymes

Sickle cell anemia (SCA) shows a pathophysiology that involves multiple changes in sickle cell erythrocytes, vaso-occlusive episodes, hemolysis, activation of inflammatory mediators, endothelial cell dysfunction, and oxidative stress. These events complicate treatment and culminate in the development of manifestations such as anemia, pain crises and multiorgan dysfunction. The aim of this study was to evaluate, in SCA patients, oxidative stress and antioxidant capacity markers, correlating them to treatment with hydroxyurea (HU), β-globin haplotypes and glutathione S-transferase polymorphisms (GSTT1, GSTM1 and GSTP1), in comparison to a control group (CG). The study groups were composed of 48 individuals without hemoglobinopathies (CG), SCA patients treated with HU [AF (+HU), N = 13] and untreated SCA patients [AF (-HU), N = 15], after informed consent. The groups were analyzed using cytological, electrophoretic, chromatographic and molecular methods and information from medical records. The GSTM1 and GSTT1 polymorphisms were determined by multiplex PCR, while the GSTP1 polymorphism by PCR-RFLP. Biochemical parameters were measured using spectrophotometric methods [TBARS, TEAC and catalase (CAT) and GST activities] and a chromatographic method [glutathione (GSH)]. The fetal Hb (Hb F) levels observed in the SCA (+HU) group (10.9%) confirmed the already well-described pharmacological effect of HU, but the SCA (-HU) group also had high Hb F levels (6.1%), which may have been influenced by genetic factors not targeted in this study. We found a higher frequency of the Bantu haplotype (48.2%), followed by the Benin (32.1%) and also Cameroon haplotypes, rare in our population, and 19.7% of atypical haplotypes. The presence of Bantu haplotype was related to higher lipid peroxidation levels in patients, but also, it conferred a differential response to HU treatment, raising Hb F levels in 52.6% (P = 0.03). The protective effect of Hb F was confirmed, because the increase in their levels resulted in a 41.3% decrease in lipid peroxidation levels (r = -0.74, P = 0.0156). The genotypic frequency of the GST polymorphisms observed was similar to that of other studies in the Brazilian population, and its association with biochemical markers revealed a significant difference only for the GSTP1 polymorphism, where patients with genotype V/V showed higher GSH and TEAC levels (P = 0.04 and P = 0.03, respectively) compared to patients with genotype I/I. The TBARS levels were about five to eight times higher in the SCA (+HU) and SCA (-HU) groups, respectively, compared to controls, and HU produced a 35.2% decrease in lipid peroxidation levels in the SCA (+HU) group (P < 0.0001). Moreover, the SCA (+HU) group showed higher TEAC levels when compared to CG (P = 0.002). We did not find any significant difference in GST activity between the groups studied (P = 0.76), but CAT activity was about 17 and 30% lower in SCA (+HU) and SCA (-HU) groups, respectively (P < 0.00001). Plasma GSH levels were ~2 times higher in SCA patients than in the control group (P = 0.0005) and showed a positive correlation with TBARS levels, confirming its antioxidant function. HU treatment contributed to higher CAT activity and TEAC levels and lower lipid peroxidation, and its pharmacological effect showed a “haplotype-dependent” response. These findings may contribute to elucidating the potential of HU in ameliorating oxidative stress in SCA subjects.

Synthesis of sulforaphane and inhibition of cytochrome P450 enzymes as a basis for antigenotoxicity

Many dietary factors have been associated with a decreased risk of developing cancer. One potential mechanism by which these factors, chemopreventors, protect against cancer may be via alteration of carcinogen metabolism. The broccoli constituent sulforaphane (1-isothiocyanate-4-methylsulinylbutane) (CH3-S0-(CH2)4-NCS) has been isolated as a potential inducer of phase II detoxification enzymes and also protects rodents against 9,10-dimethyl-1,2-benz[aJanthracene-induced mammary tumours. The ability of sulforaphane to also modulate phase I activation enzymes (cytochrome P450) (CYP450) was studied here. Sulforaphane was synthesised with an overall yield of 15%, essentially via 1-methylsulfinylphthalimidobutane, which was oxidised to the sulfoxide moiety. Deprotective removal of phthalimide yielded the amine, which was converted into sulforaphane by reaction with N,N'-thionocarbonyldiimidazole. Purity (95 %) was checked by 1H-NMR,13C-NMR and infrared and mass spectrometry.Sulforaphane was a competitive inhibitor of CYP2E1 in acetone-induced Sprague-Dawley rat microsomes (Ki 37.9 ± 4.5μM), as measured by the p-nitrophenol hydroxylase assay. Ethoxyresorufin deethylase activity (EROD), a measurement of CYP1A activity, was also inhibited by sulforaphane (100μM) but was not competitive, and a preincubation time-dependence was observed. In view of these results, the capacity of sulforaphane to inhibit N-nitrosodimethylamine (NDMA)-induced genotoxicity (CYP2E1-mediated) was studied using mouse liver activation systems. Sulforaphane (>0.8μM) inhibited the mutagenicity of NDMA (4.4 mg/plate) in Salmonella typhimurium strain TA100 after pre-incubation for 45 min with acetone-induced liver 9000 g supernatants from Balb/c mice. Unscheduled DNA synthesis induced by NDMA (33μ5 M) in mouse hepatocytes was also reduced by sulforaphane in a concentration-dependent manner (0.064-20μM). Sulforaphane was not genotoxic itself in any of these systems and cytotoxic only at high concentrations (>0.5 mM and > 40μM respectively). The ability of sulforaphane to modulate the orthologous human enzymes was studied using a human epithelial liver cell line (THLE) expressing individual human CYP450 isoenzymes. Using the Comet assay (a measurement of DNA strand breakage under alkaline conditions), NDMA (0.01-1μg/ml) and IQ (0.1-10μg/ml) were used to produce strand breaks in T5-2E1 cells (expressing human CYP2E1) and T5-1A2 cells (expressing human CYP1A2) respectively, however no response was observed in T5-neo cells (without CYP450 cDNA transfection). Sulforaphane inhibited both NDMA and IQ-induced DNA strand breakage in a concentration-dependent manner (0.1-10μM).The inhibition of metabolic activation as a basis for the antigenotoxic action of sulforaphane in these systems (bacteria, rodent hepatocytes and human cells) is further supported by the lack of this chemopreventor to influence NaN3 mutagenicity in S. typhimurium and H202-induced DNA strand breakage in T5-neo cells. These findings suggest that inhibition of CYP2E1 and CYP1A by sulforaphane may contribute to its chemoprotective potential.

Cellular polarity in aging: role of redox regulation and nutrition

Cellular polarity concerns the spatial asymmetric organization of cellular components and structures. Such organization is important not only for biological behavior at the individual cell level, but also for the 3D organization of tissues and organs in living organisms. Processes like cell migration and motility, asymmetric inheritance, and spatial organization of daughter cells in tissues are all dependent of cell polarity. Many of these processes are compromised during aging and cellular senescence. For example, permeability epithelium barriers are leakier during aging; elderly people have impaired vascular function and increased frequency of cancer, and asymmetrical inheritance is compromised in senescent cells, including stem cells. Here, we review the cellular regulation of polarity, as well as the signaling mechanisms and respective redox regulation of the pathways involved in defining cellular polarity. Emphasis will be put on the role of cytoskeleton and the AMP-activated protein kinase pathway. We also discuss how nutrients can affect polarity-dependent processes, both by direct exposure of the gastrointestinal epithelium to nutrients and by indirect effects elicited by the metabolism of nutrients, such as activation of antioxidant response and phase-II detoxification enzymes through the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2). In summary, cellular polarity emerges as a key process whose redox deregulation is hypothesized to have a central role in aging and cellular senescence.

Elements of olfactory reception in adult Drosophila melanogaster.

The olfactory system of Drosophila has become an attractive and simple model to investigate olfaction because it follows the same organizational principles of vertebrates, and the results can be directly applied to other insects with economic and sanitary relevance. Here, we review the structural elements of the Drosophila olfactory reception organs at the level of the cells and molecules involved. This article is intended to reflect the structural basis underlying the functional variability of the detection of an olfactory universe composed of thousands of odors. At the genetic level, we further detail the genes and transcription factors (TF) that determine the structural variability. The fly's olfactory receptor organs are the third antennal segments and the maxillary palps, which are covered with sensory hairs called sensilla. These sensilla house the odorant receptor neurons (ORNs) that express one or few odorant receptors in a stereotyped pattern regulated by combinations of TF. Also, perireceptor events, such as odor molecules transport to their receptors, are carried out by odorant binding proteins. In addition, the rapid odorant inactivation to preclude saturation of the system occurs by biotransformation and detoxification enzymes. These additional events take place in the lymph that surrounds the ORNs. We include some data on ionotropic and metabotropic olfactory transduction, although this issue is still under debate in Drosophila.

Genome sequencing of the plant pathogen Taphrina deformans, the causal agent of peach leaf curl.

Taphrina deformans is a fungus responsible for peach leaf curl, an important plant disease. It is phylogenetically assigned to the Taphrinomycotina subphylum, which includes the fission yeast and the mammalian pathogens of the genus Pneumocystis. We describe here the genome of T. deformans in the light of its dual plant-saprophytic/plant-parasitic lifestyle. The 13.3-Mb genome contains few identifiable repeated elements (ca. 1.5%) and a relatively high GC content (49.5%). A total of 5,735 protein-coding genes were identified, among which 83% share similarities with other fungi. Adaptation to the plant host seems reflected in the genome, since the genome carries genes involved in plant cell wall degradation (e.g., cellulases and cutinases), secondary metabolism, the hallmark glyoxylate cycle, detoxification, and sterol biosynthesis, as well as genes involved in the biosynthesis of plant hormones. Genes involved in lipid metabolism may play a role in its virulence. Several locus candidates for putative MAT cassettes and sex-related genes akin to those of Schizosaccharomyces pombe were identified. A mating-type-switching mechanism similar to that found in ascomycetous yeasts could be in effect. Taken together, the findings are consistent with the alternate saprophytic and parasitic-pathogenic lifestyles of T. deformans. IMPORTANCE: Peach leaf curl is an important plant disease which causes significant losses of fruit production. We report here the genome sequence of the causative agent of the disease, the fungus Taphrina deformans. The genome carries characteristic genes that are important for the plant infection process. These include (i) proteases that allow degradation of the plant tissues; (ii) secondary metabolites which are products favoring interaction of the fungus with the environment, including the host; (iii) hormones that are responsible for the symptom of severely distorted leaves on the host; and (iv) drug detoxification enzymes that confer resistance to fungicides. The availability of the genome allows the design of new drug targets as well as the elaboration of specific management strategies to fight the disease.

The effect of sixteen medicinal plants used in the Brazilian pharmacopoeia on the expression and activity of glutathione S-transferase in hepatocytes and leukemia cells

Glutathione S-transferase (GST) is a family of enzymes involved in the detoxification of electrophilic compounds. Different classes of GST are expressed in various organs, such as liver, lungs, stomach and others. Expression of GST can be modulated by diet components and plant-derived compounds. The importance of controlling GST expression is twofold: increasing levels of GST are beneficial to prevent deleterious effects of toxic and carcinogenic compounds, while inhibition of GST in tumor cells may help overcoming tumor resistance to chemotherapy. A screening of 16 plants used in the Brazilian pharmacopoeia tested their effects on GST expression in hepatocytes and Jurkat (leukemia) T-cells. The methanol extracts of five plants inhibited GST expression in hepatocytes. Three plants significantly inhibited and four others induced GST expression in Jurkat cells. Among these, the extracts of Bauhinia forficata Link. (Leguminosae) and Cecropia pachystachya Trec. (Urticaceae) inhibited GST expression at relatively low concentrations. With the exception of B. forficata, all plants were cytotoxic when administered to Jurkat cells at high doses (1 mg/mL) and some extracts were considerably cytotoxic even at lower concentrations.

Cloning, expression, purification and characterization of recombinant glutathione-S-transferase from Xylella fastidiosa

Xylella fastidiosa is an important pathogen bacterium transmitted by xylem-feedings leafhoppers that colonizes the xylem of plants and causes diseases on several important crops including citrus variegated chlorosis (CVC) in orange and lime trees. Glutathione-S-transferases (GST) form a group of multifunctional isoenzymes that catalyzes both glutathione (GSH)-dependent conjugation and reduction reactions involved in the cellular detoxification of xenobiotic and endobiotic compounds. GSTs are the major detoxification enzymes found in the intracellular space and mainly in the cytosol from prokaryotes to mammals, and may be involved in the regulation of stress-activated signals by suppressing apoptosis signal-regulating kinase 1. In this study, we describe the cloning of the glutathione-S-transferase from X. fastidiosa into pET-28a(+) vector, its expression in Escherichia coli, purification and initial structural characterization. The purification of recombinant xfGST (rxfGST) to near homogeneity was achieved using affinity chromatography and size-exclusion chromatography (SEC). SEC demonstrated that rxfGST is a homodimer in solution. The secondary and tertiary structures of recombinant protein were analyzed by circular dichroism and fluorescence spectroscopy, respectively. The enzyme was assayed for activity and the results taken together indicated that rxfGST is a stable molecule, correctly folded, and highly active. Several members of the GST family have been extensively studied. However, xfGST is part of a less-studied subfamily which yet has not been structurally and biochemically characterized. In addition, these studies should provide a useful basis for future studies and biotechnological approaches of rxfGST. (C) 2008 Elsevier Inc. All rights reserved.

Cloning, expression, purification and characterization of recombinant glutathione-S-transferase from Xylella fastidiosa

Xylella fastidiosa is an important pathogen bacterium transmitted by xylem-feedings leafhoppers that colonizes the xylem of plants and causes diseases on several important crops including citrus variegated chlorosis (CVC) in orange and lime trees. Glutathione-S-transferases (GST) form a group of multifunctional isoenzymes that catalyzes both glutathione (GSH)-dependent conjugation and reduction reactions involved in the cellular detoxification of xenobiotic and endobiotic compounds. GSTs are the major detoxification enzymes found in the intracellular space and mainly in the cytosol from prokaryotes to mammals, and may be involved in the regulation of stress-activated signals by suppressing apoptosis signal-regulating kinase 1. In this study, we describe the cloning of the glutathione-S-transferase from X. fastidiosa into pET-28a(+) vector, its expression in Escherichia coli, purification and initial structural characterization. The purification of recombinant xfGST (rxfGST) to near homogeneity was achieved using affinity chromatography and size-exclusion chromatography (SEC). SEC demonstrated that rxfGST is a homodimer in solution. The secondary and tertiary structures of recombinant protein were analyzed by circular dichroism and fluorescence spectroscopy, respectively. The enzyme was assayed for activity and the results taken together indicated that rxfGST is a stable molecule, correctly folded, and highly active. Several members of the GST family have been extensively studied. However, xfGST is part of a less-studied subfamily which yet has not been structurally and biochemically characterized. In addition, these studies should provide a useful basis for future studies and biotechnological approaches of rxfGST. (C) 2008 Elsevier B.V. All rights reserved.

Nrf2 is essential for protection against acute pulmonary injury in mice

Nrf2 is a member of the “cap ‘n’ collar” family of transcription factors. These transcription factors bind to the NF-E2 binding sites (GCTGAGTCA) that are essential for the regulation of erythroid-specific genes. Nrf2 is expressed in a wide range of tissues, many of which are sites of expression for phase 2 detoxification genes. Nrf2−/− mice are viable and have a normal phenotype under normal laboratory conditions. The NF-E2 binding site is a subset of the antioxidant response elements that have the sequence GCNNNGTCA. The antioxidant response elements are regulatory sequences found on promoters of several phase 2 detoxification genes that are inducible by xenobiotics and antioxidants. We report here that Nrf2−/− mice are extremely susceptible to the administration of the antioxidant butylated hydroxytoluene. With doses of butylated hydroxytoluene that are tolerated by wild-type mice, the Nrf2−/− mice succumb from acute respiratory distress syndrome. Gene expression studies show that the expression of several detoxification enzymes is altered in the Nrf2−/− mice. The Nrf2−/− mice may prove to be a good in vivo model for toxicological studies. As oxidative damage causes DNA breakage, these mice may also be useful for testing carcinogenic agents.

Changes in global gene expression patterns during development and maturation of the rat kidney

We set out to define patterns of gene expression during kidney organogenesis by using high-density DNA array technology. Expression analysis of 8,740 rat genes revealed five discrete patterns or groups of gene expression during nephrogenesis. Group 1 consisted of genes with very high expression in the early embryonic kidney, many with roles in protein translation and DNA replication. Group 2 consisted of genes that peaked in midembryogenesis and contained many transcripts specifying proteins of the extracellular matrix. Many additional transcripts allied with groups 1 and 2 had known or proposed roles in kidney development and included LIM1, POD1, GFRA1, WT1, BCL2, Homeobox protein A11, timeless, pleiotrophin, HGF, HNF3, BMP4, TGF-α, TGF-β2, IGF-II, met, FGF7, BMP4, and ganglioside-GD3. Group 3 consisted of transcripts that peaked in the neonatal period and contained a number of retrotransposon RNAs. Group 4 contained genes that steadily increased in relative expression levels throughout development, including many genes involved in energy metabolism and transport. Group 5 consisted of genes with relatively low levels of expression throughout embryogenesis but with markedly higher levels in the adult kidney; this group included a heterogeneous mix of transporters, detoxification enzymes, and oxidative stress genes. The data suggest that the embryonic kidney is committed to cellular proliferation and morphogenesis early on, followed sequentially by extracellular matrix deposition and acquisition of markers of terminal differentiation. The neonatal burst of retrotransposon mRNA was unexpected and may play a role in a stress response associated with birth. Custom analytical tools were developed including “The Equalizer” and “eBlot,” which contain improved methods for data normalization, significance testing, and data mining.

Antitumor promotion by phenolic antioxidants: inhibition of AP-1 activity through induction of Fra expression.

Induction of phase 2 detoxification enzymes by phenolic antioxidants can account for prevention of tumor initiation but cannot explain why these compounds inhibit tumor promotion. Phase 2 genes are induced through an antioxidant response element (ARE). Although the ARE resembles an AP-1 binding site, we show that the major ARE binding and activating protein is not AP-1. Interestingly, AP-1 DNA binding activity was induced by the phenolic antioxidant tert-butylhydroquinone (BHQ), but the induction of AP-1 transcriptional activity by the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) was inhibited by this compound. BHQ induced expression of c-jun, junB, fra-1, and fra-2, which encode AP-1 components, but was a poor inducer of c-fos and had no effect on fosB. Like c-Fos and FosB, the Fra proteins heterodimerize with Jun proteins to form stable AP-1 complexes. However, Fra-containing AP-1 complexes have low transactivation potential. Furthermore, Fra-1 repressed AP-1 activity induced by either TPA or expression of c-Jun and c-Fos. We therefore conclude that inhibitory AP-1 complexes composed of Jun-Fra heterodimers, induced by BHQ, antagonize the transcriptional effects of the tumor promoter TPA, which are mediated by Jun-Fos heterodimers. Since AP-1 is an important mediator of tumor promoter action, these findings may explain the anti-tumor-promoting activity of phenolic antioxidants.

Exposure to toxic Alexandrium minutum activates the detoxifying and antioxidant systems in gills of the oyster Crassostrea gigas

Harmful algal blooms of Alexandrium spp. dinoflagellates regularly occur in French coastal waters contaminating shellfish. Studies have demonstrated that toxic Alexandrium spp. disrupt behavioural and physiological processes in marine filter-feeders, but molecular modifications triggered by phycotoxins are less well understood. This study analyzed the mRNA levels of 7 genes encoding antioxidant/detoxifying enzymes in gills of Pacific oysters (Crassostrea gigas) exposed to a cultured, toxic strain of A. minutum, a producer of paralytic shellfish toxins (PST) or fed Tisochrysis lutea (T. lutea, formerly Isochrysis sp., clone Tahitian (T. iso)), a non-toxic control diet, in four repeated experiments. Transcript levels of sigma-class glutathione S-transferase (GST), glutathione reductase (GR) and ferritin (Fer) were significantly higher in oysters exposed to A. minutum compared to oysters fed T. lutea. The detoxification pathway based upon glutathione (GSH)-conjugation of toxic compounds (phase II) is likely activated, and catalyzed by GST. This system appeared to be activated in gills probably for the detoxification of PST and/or extra-cellular compounds, produced by A. minutum. GST, GR and Fer can also contribute to antioxidant functions to prevent cellular damage from increased reactive oxygen species (ROS) originating either from A. minutum cells directly, from oyster hemocytes during immune response, or from other gill cells as by-products of detoxification.

he genome and genetics of a high oxidative stress tolerant Serratia sp. LCN16 isolated from the plant parasitic nematode Bursaphelenchus xylophilus

Background: Pine wilt disease (PWD) is a worldwide threat to pine forests, and is caused by the pine wood nematode (PWN) Bursaphelenchus xylophilus. Bacteria are known to be associated with PWN and may have an important role in PWD. Serratia sp. LCN16 is a PWN-associated bacterium, highly resistant to oxidative stress in vitro, and which beneficially contributes to the PWN survival under these conditions. Oxidative stress is generated as a part of the basal defense mechanism used by plants to combat pathogenic invasion. Here, we studied the biology of Serratia sp. LCN16 through genome analyses, and further investigated, using reverse genetics, the role of two genes directly involved in the neutralization of H2O2, namely the H2O2 transcriptional factor oxyR; and the H2O2-targeting enzyme, catalase katA. Results: Serratia sp. LCN16 is phylogenetically most closely related to the phytosphere group of Serratia, which includes S. proteamaculans, S. grimessi and S. liquefaciens. Likewise, Serratia sp. LCN16 shares many features with endophytes (plant-associated bacteria), such as genes coding for plant polymer degrading enzymes, iron uptake/ transport, siderophore and phytohormone synthesis, aromatic compound degradation and detoxification enzymes. OxyR and KatA are directly involved in the high tolerance to H2O2 of Serratia sp. LCN16. Under oxidative stress, Serratia sp. LCN16 expresses katA independently of OxyR in contrast with katG which is under positive regulation of OxyR. Serratia sp. LCN16 mutants for oxyR (oxyR::int(614)) and katA (katA::int(808)) were sensitive to H2O2 in relation with wild-type, and both failed to protect the PWN from H2O2-stress exposure. Moreover, both mutants showed different phenotypes in terms of biofilm production and swimming/swarming behaviors. Conclusions: This study provides new insights into the biology of PWN-associated bacteria Serratia sp. LCN16 and its extreme resistance to oxidative stress conditions, encouraging further research on the potential role of this bacterium in interaction with PWN in planta environment.