Cystathionine gamma-lyase is a component of cystine-mediated oxidative defense in Lactobacillus reuteri BR11

Influence of nitrogen sources on the tolerance of Lacticaseibacillus rhamnosus to heat stress and oxidative stress

It has been found that 32 genes related to nitrogen source metabolism in Lacticaseibacillus rhamnosus are downregulated under both heat stress and oxidative stress. In this study, the influence of different nitrogen sources within the growth medium on the tolerance of L. rhamnosus to heat stress and oxidative stress was investigated. Tryptone-free MRS was found to enhance the tolerance of L. rhamnosus hsryfm 1301 to heat stress and oxidative stress during the whole growth period, and this result was universal for all L. rhamnosus species analyzed. The strongest strengthening effect occurred when the OD₆₀₀ value reached 2.0, at which the survival rates under heat stress and oxidative stress increased 130-fold and 40-fold, respectively. After supplementing phenylalanine, isoleucine, glutamate, valine, histidine, or tryptophan into the tryptone-free MRS, the tolerance of L. rhamnosus to heat stress and oxidative stress exhibited a sharp drop. The spray drying survival rate of L. rhamnosus hsryfm 1301 cultured in the tryptone-free MRS rose to 75% (from 30%), and the spray dried powder also performed better in the experimentally simulated gastrointestinal digestion. These results showed that decreasing the intake of amino acids is an important mechanism for L. rhamnosus to tolerate heat stress and oxidative stress. When L. rhamnosus is cultured for spray drying, the concentration of the nitrogen source's components should be an important consideration.

Influence of Redox Imbalances on the Transposition of Insertion Sequences in Deinococcus geothermalis

The transposition of insertion sequence elements was evaluated among different Deinococcus geothermalis lineages, including the wild-type, a cystine importer-disrupted mutant, a complemented strain, and a cystine importer-overexpressed strain. Cellular growth reached early exponential growth at OD₆₀₀ 2.0 and late exponential growth at OD₆₀₀ 4.0. Exposing the cells to hydrogen peroxide (80–100 mM) resulted in the transposition of insertion sequences (ISs) in genes associated with the carotenoid biosynthesis pathway. Particularly, ISDge7 (an IS5 family member) and ISDge5 (an IS701 family member) from the cystine importer-disrupted mutant were transposed into phytoene desaturase (dgeo_0524) via replicative transposition. Further, the cystine importer-overexpressed strain Δdgeo_1985R showed transposition of both ISDge2 and ISDge5 elements. In contrast, IS transposition was not detected in the complementary strain. Interestingly, a cystine importer-overexpressing strain exhibited streptomycin resistance, indicating that point mutation occurred in the rpsL (dgeo_1873) gene encoding ribosomal protein S12. qRT-PCR analyses were then conducted to evaluate the expression of oxidative stress response genes, IS elements, and low-molecular-weight thiol compounds such as mycothiol and bacillithiol. Nevertheless, the mechanisms that trigger IS transposition in redox imbalance conditions remain unclear. Here, we report that the active transposition of different IS elements was affected by intracellular redox imbalances caused by cystine importer deficiencies or overexpression.

Characterization of γ-glutamyl cysteine ligases from Limosilactobacillus reuteri producing kokumi-active γ-glutamyl dipeptides

γ-Glutamyl cysteine ligases (Gcls) catalyze the first step of glutathione synthesis in prokaryotes and many eukaryotes. This study aimed to determine the biochemical properties of three different Gcls from strains of Limosilactobacillus reuteri that accumulate γ-glutamyl dipeptides. Gcl1, Gcl2, and Gcl3 were heterologously expressed in Escherichia coli and purified by affinity chromatography. Gcl1, Gcl2, and Gcl2 exhibited biochemical with respect to the requirement for metal ions, the optimum pH and temperature of activity, and the kinetic constants for the substrates cysteine and glutamate. The substrate specificities of the three Gcls to 14 amino acids were assessed by liquid chromatography-mass spectrometry. All three Gcls converted ala, met, glu, and gln into the corresponding γ-glutamyl dipeptides. None of the three were active with val, asp, and his. Gcl1 and Gcl3 but not Gcl2 formed γ-glu-leu, γ-glu-ile, and γ-glu-phe; Gcl3 exhibited stronger activity with gly, pro, and asp when compared to Gcl2. Phylogenetic analysis of Gcl and the Gcl-domain of GshAB in lactobacilli demonstrated that most of Gcls were present in heterofermentative lactobacilli, while GshAB was identified predominantly in homofermentative lactobacilli. This distribution suggests a different ecological role of the enzyme in homofermentative and heterofermentative lactobacilli. In conclusion, three Gcls exhibited similar biochemical properties but differed with respect to their substrate specificity and thus the synthesis of kokumi-active γ-glutamyl dipeptides. KEY POINTS: • Strains of Limosilactobacillus reuteri encode for up to 3 glutamyl cysteine ligases. • Gcl1, Gcl2, and Gcl3 of Lm. reuteri differ in their substrate specificity. • Gcl1 and Gcl3 produce kokumi-active dipeptides.

Genomic and physiological insights into the lifestyle of Bifidobacterium species from water kefir

Water kefir is a fermented beverage employing a natural microbial consortium, which harbours bifidobacteria, namely Bifidobacterium aquikefiri and Bifidobacterium tibiigranuli. However, little information is available on their metabolic properties or role in the consortium. In this study, we combined genomic and physiologic investigations to predict and characterize the properties of these organisms and their possible role in the consortium. When comparing the genomes of these psychrotrophic organisms with that of the three selected mesophilic probiotic Bifidobacterium strains, we could find 143 genes shared by the 3 known isolates of bifidobacteria from water kefir that do not occur in the probiotic strains. These include genes involved in acid and oxygen tolerance. In addition, their genomically predicted carbohydrate usage and transport suggest adaptation to sucrose and other plant-related sugars. Furthermore, they proved prototrophic for all amino acids in vitro, which enables them to cope with the strong amino acid limitation in water kefir.

Redox potential change by the cystine importer affected on enzymatic antioxidant protection in Deinococcus geothermalis

Radiation resistant bacteria genus Deinococcus species were well studied on DNA repair and anti-oxidative stress response mechanisms. There are many protection factors as enzymatic and nonenzymatic involved. One of them is intracellular redox potential as like thiol compounds including cysteine acts as primary protectant against oxidation stress. A gene cluster consisting of the genes Dgeo_1986 and Dgeo_1987 of Deinococcus geothermalis was identified as a cystine importer. The expression levels of dgeo_1986 and dgeo_1987 were up-regulated by over 60-fold and 4-fold during the late exponential (L) growth phase, respectively. The double-knockout mutant of dgeo_1986 and dgeo_1987 was reduced in cystine and thiol concentrations and leading to enhanced sensitivity against H₂O₂ stress. The expression of catalase (Dgeo_2728) as an enzymatic anti-oxidant is more induced in the wild-type strain than the Δdgeo_1986-87 strain at the late growth phase. The expression level of the oxidative stress response regulator OxyR (Dgeo_1888) is dependent on the intracellular redox balance. That is, when the intracellular thiol content was reduced in the wild-type strain during the L phase, OxyR was clearly induced. Interestingly, the expression level of OxyR was higher in the Δdgeo_1986-87 strain than in the wild-type strain upon H₂O₂ treatment. Although OxyR was induced by H₂O₂ treatment in Δdgeo_1986-87 strain, where intracellular redox potential of cystine was reduced as a thiol compound due to reduced cystine import, the relative level of expression of catalase was unexpectedly down-regulated. Therefore, the catalase induction system as an enzymatic antioxidant protection should be affected via the cystine importer but not rely on the OxyR controlled manner.

Complex Responses to Hydrogen Peroxide and Hypochlorous Acid by the Probiotic Bacterium Lactobacillus reuteri

Inflammatory diseases of the gut are associated with increased intestinal oxygen concentrations and high levels of inflammatory oxidants, including hydrogen peroxide (H₂O₂) and hypochlorous acid (HOCl), which are antimicrobial compounds produced by the innate immune system. This contributes to dysbiotic changes in the gut microbiome, including increased populations of proinflammatory enterobacteria (Escherichia coli and related species) and decreased levels of health-associated anaerobic Firmicutes and Bacteroidetes The pathways for H₂O₂ and HOCl resistance in E. coli have been well studied, but little is known about how commensal and probiotic bacteria respond to inflammatory oxidants. In this work, we have characterized the transcriptomic response of the anti-inflammatory, gut-colonizing Gram-positive probiotic Lactobacillus reuteri to both H₂O₂ and HOCl. L. reuteri mounts distinct but overlapping responses to each of these stressors, and both gene expression and survival were strongly affected by the presence or absence of oxygen. Oxidative stress response in L. reuteri required several factors not found in enterobacteria, including the small heat shock protein Lo18, polyphosphate kinase 2, and RsiR, an L. reuteri-specific regulator of anti-inflammatory mechanisms.IMPORTANCE Reactive oxidants, including hydrogen peroxide and hypochlorous acid, are antimicrobial compounds produced by the immune system during inflammation. Little is known, however, about how many important types of bacteria present in the human microbiome respond to these oxidants, especially commensal and other health-associated species. We have now mapped the stress response to both H₂O₂ and HOCl in the intestinal lactic acid bacterium Lactobacillus reuteri.

γ-Glutamyl Cysteine Ligase of Lactobacillus reuteri Synthesizes γ-Glutamyl Dipeptides in Sourdough

Kokumi-active γ-glutamyl dipeptides (γ-GPs) accumulate in fermented food. γ-Glutamyl transferase, glutaminase, glutathione synthetase, and γ-glutamyl cysteine ligase (GCL) may synthesize γ-GPs. The genome of Lactobacillus reuteri encodes GCL but not glutathione synthetase or glutamyl transferase; therefore, this study investigated the role of GCL in γ-GP synthesis by L. reuteri LTH5448. Phylogenomic analysis of gcl in lactobacilli demonstrated that three genes coding for GCL are present in L. reuteri; two of these are present in L. reuteri LTH5448. Two deletion mutants of L. reuteri LTH5448, L. reuteri LTH5448Δ gcl1 and LTH5448Δ gcl1Δ gcl2, were constructed by double crossover mutagenesis. Growth and oxygen resistance of the mutants were comparable to the wild type. γ-Glu-Glu, γ-Glu-Leu, γ-Glu-Ile, γ-Glu-Val, and γ-Glu-Cys were quantified in buffer and sourdough fermentations by liquid chromatography-mass spectrometry. The wild type and L. reuteri Δ gcl1 but not Δ gcl1Δ gcl2 converted amino acids to γ-Glu-Cys. γ-Glu-Ile accumulation was reduced in both mutants; however, the disruption of gcl did not alter the biosynthesis of the other γ-GPs. In conclusion, gcl1 in L. reuteri mediates γ-Glu-Ile synthesis, gcl2 mediates γ-Glu-Cys synthesis, but neither gene affected synthesis of other γ-GPs. This study facilitates selection of starter cultures that synthesize γ-Glu peptides with kokumi activity and, thus, improve the taste of fermented foods.

Phenotypic Diversity of Lactobacillus sakei Strains

Lactobacillus sakei is a lactic acid bacteria (LAB) species highly adapted to the meat environment. For this reason, selected strains are often used as starter culture in the production of fermented sausages, especially in Mediterranean countries. It often represents the dominant species in these products and can maintain its viability during all the ripening period, which can take also some months. This ability is guaranteed by the possibility of the species to obtain energy through pathways active even when hexoses are depleted. This species is characterized by a relevant genetic and phenotypic diversity and its metabolism can be further affected by the growth condition applied. In this work we investigate the metabolic responses of six different L. sakei in a synthetic medium (DM) containing defined amounts of amino acids in relation to temperature and NaCl concentration. In addition, the activities of cells pre-grown in presence of glucose o ribose were tested. Arginine was efficiently up-taken with the exception of the type strain DSMZ 20017^t. Other amino acids (i.e., serine, asparagine, cysteine, and methionine) were metabolized through potentially energetic pathways which start from pyruvate accumulation, as demonstrated by the organic acid accumulation trend in the condition tested, especially in DM without sugar added. The presence of excesses of pyruvate deriving from amino acids lead to the accumulation of diacetyl and acetoin by all the strains when sugars were added. This approach allowed a deeper insight into the phenotypic variability of the species and improved the comprehension of the metabolic pathways adopted by L. sakei to survive and grow in restrictive conditions such as those found in fermented sausages during fermentations. Thus, the results obtained are useful information for improving and optimizing the use of such strains as starter culture for these products.

Structural and functional studies of pyruvate carboxylase regulation by cyclic di-AMP in lactic acid bacteria

Cyclic di-3',5'-adenosine monophosphate (c-di-AMP) is a broadly conserved bacterial second messenger that has been implicated in a wide range of cellular processes. Our earlier studies showed that c-di-AMP regulates central metabolism in Listeria monocytogenes by inhibiting its pyruvate carboxylase (LmPC), a biotin-dependent enzyme with biotin carboxylase (BC) and carboxyltransferase (CT) activities. We report here structural, biochemical, and functional studies on the inhibition of Lactococcus lactis PC (LlPC) by c-di-AMP. The compound is bound at the dimer interface of the CT domain, at a site equivalent to that in LmPC, although it has a distinct binding mode in the LlPC complex. This binding site is not well conserved among PCs, and only a subset of these bacterial enzymes are sensitive to c-di-AMP. Conformational changes in the CT dimer induced by c-di-AMP binding may be the molecular mechanism for its inhibitory activity. Mutations of residues in the binding site can abolish c-di-AMP inhibition. In L. lactis, LlPC is required for efficient milk acidification through its essential role in aspartate biosynthesis. The aspartate pool in L. lactis is negatively regulated by c-di-AMP, and high aspartate levels can be restored by expression of a c-di-AMP-insensitive LlPC. LlPC has high intrinsic catalytic activity and is not sensitive to acetyl-CoA activation, in contrast to other PC enzymes.

Glutathione biosynthesis and activity of dependent enzymes in food-grade lactic acid bacteria harbouring multidomain bifunctional fusion gene (gshF)

AIMS

To assess glutathione (GSH) biosynthesis ability and activity of dependent enzymes in food-grade lactic acid bacteria (LAB) and correlating with genomic information on GSH system in LAB.

METHODS AND RESULTS

Whole-genome sequences of 26 food-grade LAB were screened for the presence/absence of a set of genes involved in de novo GSH system. Multiple strains of Streptococcus thermophilus (37), Lactobacillus casei (37), Lactobacillus rhamnosus (4), Lactobacillus paracasei (8) Lactobacillus plantarum (23) and Lactobacillus fermentum (22) were screened for biochemical evidence of the GSH system. Multiple sequence analysis of GshF sequences was carried out for comparing the genomic signatures between GSH-producing and nonproducing species.

CONCLUSIONS

Streptococcus thermophilus was found to have de novo GSH biosynthesis as well as import ability. Lactobacillus sp. were negative for GSH synthesis but could import it from the medium. All the species exhibited prolific GSH reductase and peroxidase activity. Sequence analysis revealed the absence of key amino acid residues as well as a truncated N-terminal region in lactobacilli.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study provides a comprehensive view on the status of an important antioxidative system (the GSH system) in LAB and is expected to serve as a primer for future work on the mechanistic role of GSH in the group.

Oxidative stress response of Deinococcus geothermalis via a cystine importer

A cystine-dependent anti-oxidative stress response is characterized in Deinococcus geothermalis for the first time. Nevertheless, the same transcriptional directed Δdgeo_1985F mutant strain was revealed to have an identical phenotype to the wild-type strain, while the reverse transcriptional directed Δdgeo_1985R mutant strain was more resistant to oxidative stress at a certain concentration of H₂O₂ than the wild-type strain. The wild-type and mutant strains expressed equal levels of superoxide dismutase and catalase under H₂O₂-induced stress. Although the expression levels of the general DNA-damage response-related genes recA, pprA, ddrA, and ddrB were up-regulated by more than five-fold in the wild-type strain relative to the Δdgeo_1985R mutant strain, the mutant strain had a higher survival rate than the wild-type under H₂O₂ stress. The Δdgeo_1985R mutant strain highly expressed a cystine-transporter gene (dgeo_1986), at levels 150-fold higher than the wild-type strain, leading to the conclusion that this cystine transporter might be involved in the defensive response to H₂O₂ stress. In this study, the cystine transporter was identified and characterized through membrane protein expression analysis, a cystine-binding assay, and assays of intracellular H₂O₂, cysteine, and thiol levels. The genedisrupted mutant strain of the cystine importer revealed high sensitivity to H₂O₂ and less absorbed cystine, resulting in low concentrations of total thiol. Thus, the absorbed cystine via this cystine-specific importer may be converted into cysteine, which acts as a primitive defense substrate that non-enzymatically scavenges oxidative stress agents in D. geothermalis.

Characterization of the ecological role of genes mediating acid resistance in Lactobacillus reuteri during colonization of the gastrointestinal tract

Rodent-derived strains of Lactobacillus reuteri densely colonize the forestomach of mice and possess several genes whose predicted functions constitute adaptations towards an acidic environment. The objective of this study was to systematically determine which genes of L. reuteri 100-23 contribute to tolerance towards host gastric acid secretion. Genes predicted to be involved in acid resistance were inactivated, and their contribution to survival under acidic conditions was confirmed in model gastric juice. Fitness of five mutants that showed impaired in vitro acid resistance were then compared through competition experiments in ex-germ-free mice that were either treated with omeprazole, a proton-pump inhibitor that suppresses acid secretion in the stomach, or left untreated. This analysis revealed that the urease cluster was the predominant factor in mediating resistance to gastric acid production. Population levels of the mutant, which were substantially decreased in untreated mice, were almost completely restored through omeprazole, demonstrating that urease production in L. reuteri is mainly devoted to overcome gastric acid. The findings provide novel information on the mechanisms by which L. reuteri colonizes its gastric niche and demonstrate that in silico gene predictions and in vitro tests have limitations for predicting the ecological functions of colonization factors in bacterial symbionts.

Death by Cystine: an Adverse Emergent Property from a Beneficial Series of Reactions

In this issue of the Journal of Bacteriology, Chonoles Imlay et al. (K. R. Chonoles Imlay, S. Korshunov, and J. A. Imlay, J Bacteriol 197:3629-3644, 2015, http://dx.doi.org/10.1128/JB.00277-15) show that oxidative stress kills sulfur-restricted Escherichia coli grown with sublethal H2O2 when challenged with cystine. Killing requires rapid and seemingly unregulated cystine transport and equally rapid cystine reduction to cysteine. Cysteine export completes an energy-depleting futile cycle. Each reaction of the cycle could be beneficial. Together, a cystine-mediated vulnerability emerges during the transition from a sulfur-restricted to a sulfur-replete environment, perhaps because of complexities of sulfur metabolism.

Uptake of L-cystine via an ABC transporter contributes defense of oxidative stress in the L-cystine export-dependent manner in Escherichia coli

Intracellular thiols like L-cystine and L-cystine play a critical role in the regulation of cellular processes. Here we show that Escherichia coli has two L-cystine transporters, the symporter YdjN and the ATP-binding cassette importer FliY-YecSC. These proteins import L-cystine, an oxidized product of L-cystine from the periplasm to the cytoplasm. The symporter YdjN, which is expected to be a new member of the L-cystine regulon, is a low affinity L-cystine transporter (K_m = 1.1 μM) that is mainly involved in L-cystine uptake from outside as a nutrient. E. coli has only two L-cystine importers because ΔydjNΔyecS mutant cells are not capable of growing in the minimal medium containing L-cystine as a sole sulfur source. Another protein YecSC is the FliY-dependent L-cystine transporter that functions cooperatively with the L-cystine transporter YdeD, which exports L-cystine as reducing equivalents from the cytoplasm to the periplasm, to prevent E. coli cells from oxidative stress. The exported L-cystine can reduce the periplasmic hydrogen peroxide to water, and then generated L-cystine is imported back into the cytoplasm via the ATP-binding cassette transporter YecSC with a high affinity to L-cystine (K_m = 110 nM) in a manner dependent on FliY, the periplasmic L-cystine-binding protein. The double disruption of ydeD and fliY increased cellular levels of lipid peroxides. From these findings, we propose that the hydrogen peroxide-inducible L-cystine/L-cystine shuttle system plays a role of detoxification of hydrogen peroxide before lipid peroxidation occurs, and then might specific prevent damage to membrane lipids.

Metabolic fingerprint of dimethyl sulfone (DMSO2) in microbial-mammalian co-metabolism

There is growing awareness that intestinal microbiota alters the energy harvesting capacity of the host and regulates metabolism. It has been postulated that intestinal microbiota are able to degrade unabsorbed dietary components and transform xenobiotic compounds. The resulting microbial metabolites derived from the gastrointestinal tract can potentially enter the circulation system, which, in turn, affects host metabolism. Yet, the metabolic capacity of intestinal microbiota and its interaction with mammalian metabolism remains largely unexplored. Here, we review a metabolic pathway that integrates the microbial catabolism of methionine with mammalian metabolism of methanethiol (MT), dimethyl sulfide (DMS), and dimethyl sulfoxide (DMSO), which together provide evidence that supports the microbial origin of dimethyl sulfone (DMSO2) in the human metabolome. Understanding the pathway of DMSO2 co-metabolism expends our knowledge of microbial-derived metabolites and motivates future metabolomics-based studies on ascertaining the metabolic consequences of intestinal microbiota on human health, including detoxification processes and sulfur xenobiotic metabolism.

Integrated transcriptomic and proteomic analysis of the bile stress response in a centenarian-originated probiotic Bifidobacterium longum BBMN68

Bifidobacteria are natural inhabitants of the human gastrointestinal tract and well known for their health-promoting effects. Tolerance to bile stress is crucial for bifidobacteria to survive in the colon and to exert their beneficial actions. In this work, RNA-Seq transcriptomic analysis complemented with proteomic analysis was used to investigate the cellular response to bile in Bifidobacterium longum BBMN68. The transcript levels of 236 genes were significantly changed (≥ threefold, p < 0.001) and 44 proteins were differentially abundant (≥1.6-fold, p < 0.01) in B. longum BBMN68 when exposed to 0.75 g l(-1) ox-bile. The hemolysin-like protein and bile efflux systems were significantly over produced, which might prevent bile adsorption and exclude bile, respectively. The cell membrane composition was modified probably by an increase of cyclopropane fatty acid and a decrease of transmembrane proteins, resulting in a cell membrane more impermeable to bile salts. Our hypothesis was later confirmed by surface hydrophobicity assay. The transcription of genes related to xylose utilization and bifid shunt were up-regulated, which increased the production of ATP and reducing equivalents to cope with bile-induced damages in a xylan-rich colon environment. Bile salts signal the B. longum BBMN68 to gut entrance and enhance the expression of esterase and sortase associated with adhesion and colonization in intestinal tract, which was supported by a fivefold increased adhesion ability to HT-29 cells by BBMN68 upon bile exposure. Notably, bacterial one-hybrid and EMSA assay revealed that the two-component system senX3-regX3 controlled the expression of pstS in bifidobacteria and the role of this target gene in bile resistance was further verified by heterologous expression in Lactococcus lactis. Taken altogether, this study established a model for global response mechanisms in B. longum to bile.

The transcriptional response of Lactobacillus sanfranciscensis DSM 20451T and its tcyB mutant lacking a functional cystine transporter to diamide stress

As a result of its strong adaptation to wheat and rye sourdoughs, Lactobacillus sanfranciscensis has the smallest genome within the genus Lactobacillus. The concomitant absence of some important antioxidative enzymes and the inability to synthesize glutathione suggest a role of cystine transport in maintenance of an intracellular thiol balance. Diamide [synonym 1,1'-azobis(N,N-dimethylformamide)] disturbs intracellular and membrane thiol levels in oxidizing protein thiols depending on its initial concentration. In this study, RNA sequencing was used to reveal the transcriptional response of L. sanfranciscensis DSM 20451(T) (wild type [WT]) and its ΔtcyB mutant with a nonfunctional cystine transporter after thiol stress caused by diamide. Along with the different expression of genes involved in amino acid starvation, pyrimidine synthesis, and energy production, our results show that thiol stress in the wild type can be compensated through activation of diverse chaperones and proteases whereas the ΔtcyB mutant shifts its metabolism in the direction of survival. Only a small set of genes are significantly differentially expressed between the wild type and the mutant. In the WT, mainly genes which are associated with a heat shock response are upregulated whereas glutamine import and synthesis genes are downregulated. In the ΔtcyB mutant, the whole opp operon was more highly expressed, as well as a protein which probably includes enzymes for methionine transport. The two proteins encoded by spxA and nrdH, which are involved in direct or indirect oxidative stress responses, are also upregulated in the mutant. This work emphasizes that even in the absence of definitive antioxidative enzymes, bacteria with a small genome and a high frequency of gene inactivation and elimination use small molecules such as the cysteine/cystine couple to overcome potential cell damage resulting from oxidative stress.

Current status and emerging role of glutathione in food grade lactic acid bacteria

Lactic acid bacteria (LAB) have taken centre stage in perspectives of modern fermented food industry and probiotic based therapeutics. These bacteria encounter various stress conditions during industrial processing or in the gastrointestinal environment. Such conditions are overcome by complex molecular assemblies capable of synthesizing and/or metabolizing molecules that play a specific role in stress adaptation. Thiols are important class of molecules which contribute towards stress management in cell. Glutathione, a low molecular weight thiol antioxidant distributed widely in eukaryotes and Gram negative organisms, is present sporadically in Gram positive bacteria. However, new insights on its occurrence and role in the latter group are coming to light. Some LAB and closely related Gram positive organisms are proposed to possess glutathione synthesis and/or utilization machinery. Also, supplementation of glutathione in food grade LAB is gaining attention for its role in stress protection and as a nutrient and sulfur source. Owing to the immense benefits of glutathione, its release by probiotic bacteria could also find important applications in health improvement. This review presents our current understanding about the status of glutathione and its role as an exogenously added molecule in food grade LAB and closely related organisms.

Heat resistance and salt hypersensitivity in Lactococcus lactis due to spontaneous mutation of llmg_1816 (gdpP) induced by high-temperature growth

During construction of several gene deletion mutants in Lactococcus lactis MG1363 which involved a high-temperature (37.5°C) incubation step, additional spontaneous mutations were observed which resulted in stable heat resistance and in some cases salt-hypersensitive phenotypes. Whole-genome sequencing of one strain which was both heat resistant and salt hypersensitive, followed by PCR and sequencing of four other mutants which shared these phenotypes, revealed independent mutations in llmg_1816 in all cases. This gene encodes a membrane-bound stress signaling protein of the GdpP family, members of which exhibit cyclic dimeric AMP (c-di-AMP)-specific phosphodiesterase activity. Mutations were predicted to lead to single amino acid substitutions or protein truncations. An independent llmg_1816 mutant (Δ1816), created using a suicide vector, also displayed heat resistance and salt hypersensitivity phenotypes which could be restored to wild-type levels following plasmid excision. L. lactis Δ1816 also displayed improved growth in response to sublethal concentrations of penicillin G. High-temperature incubation of a wild-type industrial L. lactis strain also resulted in spontaneous mutation of llmg_1816 and heat-resistant and salt-hypersensitive phenotypes, suggesting that this is not a strain-specific phenomenon and that it is independent of a plasmid integration event. Acidification of milk by the llmg_1816-altered strain was inhibited by lower salt concentrations than the parent strain. This study demonstrates that spontaneous mutations can occur during high-temperature growth of L. lactis and that inactivation of llmg_1816 leads to temperature resistance and salt hypersensitivity.

Effects of a Lactobacillus reuteri BR11 mutant deficient in the cystine-transport system in a rat model of inflammatory bowel disease

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract associated with altered composition of the gut microbiota. Lactobacillus reuteri BR11 (BR11) has recently been reported to reduce the severity of experimental IBD because of its probiotic properties possibly attributed to a mechanism of thiol production via its unique cysteine/cystine-transport system.

AIM

We compared BR11 and a BR11 mutant deficient in the cystine-uptake system (PNG201), for their capacity to reduce the severity of experimental colitis.

METHODS

Male Sprague-Dawley rats (n = 8 per group) were gavaged (1 ml/day) with skim milk, BR11 or PNG201 (1 × 10(9) CFU/ml) for 12 days. Rats consumed either water or 2% dextran sulfate sodium in drinking water from days 6 to 12 to induce colitis. Metabolism data, disease activity index, intestinal mucin profile, and histological analyses were assessed and compared by ANOVA.

RESULTS

Assessed histologically, DSS administration resulted in significant colonic deterioration, including loss of crypt area and increased damage severity. BR11 administration only partially alleviated the DSS effects, with a minor improvement in crypt area (P < 0.05). Administration of the PNG201 mutant strain to colitic animals failed to achieve significance (P > 0.05) against the DSS control for any of the end-points. However, the mutant strain induced significantly greater (P < 0.05) histological severity compared with BR11-treated colitic animals, indicative of possible exacerbation of colitis.

CONCLUSIONS

The cystine-uptake system only minimally affects the biological effects of BR11, as evidenced by histological and macroscopic colitic changes.

Corynebacterium glutamicum as an indicator for environmental cobalt and silver stress--a proteome analysis

Cobalt and silver are toxic for cells, but mechanisms of this toxicity are largely unknown. Analysis of Corynebacterium glutamicum proteome from cells grown in control and cobalt or silver enriched media was performed by two dimensional gel electrophoresis (2DE) followed by mass spectrometry. Our results indicate that the cell adapted to cobalt stress by inducing five defense mechanisms: Scavenging of free radicals, promotion of the generation of energy, reparation of DNA, reparation and biogenesis of Fe-S cluster proteins and supporting and reparation of cell wall. In response to the detoxification of Ag+ many proteins were up-regulated, which involved reparation of damaged DNA, minimizing the toxic effect of reactive oxygen species (ROS) and energy generation. Overexpression of proteins involved in cell wall biosynthesis (1,4-alpha-glucan branching enzyme and nucleoside-diphosphate-sugar epimerase) upon cobalt stress and induction of proteins involved in energy metabolism (2-methylcitrate dehydratase and 1, 2-methylcitrate synthase) upon silver demonstrate the potential of these enzymes as biomarkers of sub-lethal Ag+ and Co toxicity.

The pleiotropic CymR regulator of Staphylococcus aureus plays an important role in virulence and stress response

We have characterized a novel pleiotropic role for CymR, the master regulator of cysteine metabolism. We show here that CymR plays an important role both in stress response and virulence of Staphylococcus aureus. Genes involved in detoxification processes, including oxidative stress response and metal ion homeostasis, were differentially expressed in a ΔcymR mutant. Deletion of cymR resulted in increased sensitivity to hydrogen peroxide-, disulfide-, tellurite- and copper-induced stresses. Estimation of metabolite pools suggests that this heightened sensitivity could be the result of profound metabolic changes in the ΔcymR mutant, with an increase in the intracellular cysteine pool and hydrogen sulfide formation. Since resistance to oxidative stress within the host organism is important for pathogen survival, we investigated the role of CymR during the infectious process. Our results indicate that the deletion of cymR promotes survival of S. aureus inside macrophages, whereas virulence of the ΔcymR mutant is highly impaired in mice. These data indicate that CymR plays a major role in virulence and adaptation of S. aureus for survival within the host.

Staphylococcus aureus is a very harmful human pathogen that is a major cause of nosocomial infections. Humans have developed sophisticated defense strategies against invading bacteria, including the innate immune response, with the generation of an oxidative burst inside phagocytic cells. Staphylococcal infections are extremely difficult to eradicate due to the remarkable capacity of these bacteria to adapt to different environmental conditions both inside and outside the host organism. Sulfur metabolism is essential for all living organisms and is tightly controlled by regulatory proteins. In this paper, we revealed an important role for CymR, a major regulator of sulfur metabolism, in adaptation of S. aureus to the host environment. Inactivation of the gene encoding this regulator in S. aureus leads to a mutant bacterium with increased vulnerability to stress conditions including oxidative stress encountered inside the host. More importantly, the deletion of the cymR gene strongly affected the interaction of S. aureus with its host, leading to impaired virulence in mice. Our results place CymR among the potential targets for attenuation of S. aureus infections.