Oxygen utilization by Lactobacillus plantarum. I. Oxygen consuming reactions

The Arsenal of Leptospira Species against Oxidants

Reactive oxygen species (ROS) are byproducts of oxygen metabolism produced by virtually all organisms living in an oxic environment. ROS are also produced by phagocytic cells in response to microorganism invasion. These highly reactive molecules can damage cellular constituents (proteins, DNA, and lipids) and exhibit antimicrobial activities when present in sufficient amount. Consequently, microorganisms have evolved defense mechanisms to counteract ROS-induced oxidative damage. Leptospira are diderm bacteria form the Spirochaetes phylum. This genus is diverse, encompassing both free-living non-pathogenic bacteria as well as pathogenic species responsible for leptospirosis, a widespread zoonotic disease. All leptospires are exposed to ROS in the environment, but only pathogenic species are well-equipped to sustain the oxidative stress encountered inside their hosts during infection. Importantly, this ability plays a pivotal role in Leptospira virulence. In this review, we describe the ROS encountered by Leptospira in their different ecological niches and outline the repertoire of defense mechanisms identified so far in these bacteria to scavenge deadly ROS. We also review the mechanisms controlling the expression of these antioxidants systems and recent advances in understanding the contribution of Peroxide Stress Regulators in Leptospira adaptation to oxidative stress.

Role of the Mn-Catalase in Aerobic Growth of Lactobacillus plantarum ATCC 14431

Lactobacilli are Gram-positive aerotolerant organisms that comprise the largest genus of Lactic Acid Bacteria (LAB). Most lactobacilli are devoid of the antioxidant enzymes, superoxide dismutases, and catalases, required for protection against superoxide radicals and hydrogen peroxide (H2O2), respectively. However, some lactobacilli can accumulate millimolar concentrations of intracellular manganese and spare the need for superoxide dismutase, while others possess non-heme catalases. L. plantarum is associated with plant materials and plays an important role in fermented foods and gut microbiomes. Therefore, understanding the effects of the environment on the growth and survival of this organism is essential for its success in relevant industrial applications. In this report, we investigated the physiological role of Mn-catalase (MnKat) in Lactobacillus plantarum ATCC 14431. To this end, we compared the physiological and morphological properties of a ΔMnkat mutant strain and its isogenic parental strain L. plantarum ATCC 14431. Our data showed that the MnKat is critical for the growth of L. plantarum ATCC 14431 in the presence of oxygen and resistance to H2O2. The aerobic growth of the mutant in presence or absence of H2O2 was improved in the Mn-rich medium (APT) as compared to the growth in MRS medium. Furthermore, under aerobic conditions the mutant strain possessed atypical cellular morphology (i.e., shorter, and fatter). In conclusion, the MnKat of L. plantarum ATCC 14431 is important for aerobic growth, protection against H2O2, and maintenance of the rod-shaped cell morphology under aerobic conditions.

Stress Physiology of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are important starter, commensal, or pathogenic microorganisms. The stress physiology of LAB has been studied in depth for over 2 decades, fueled mostly by the technological implications of LAB robustness in the food industry. Survival of probiotic LAB in the host and the potential relatedness of LAB virulence to their stress resilience have intensified interest in the field. Thus, a wealth of information concerning stress responses exists today for strains as diverse as starter (e.g., Lactococcus lactis), probiotic (e.g., several Lactobacillus spp.), and pathogenic (e.g., Enterococcus and Streptococcus spp.) LAB. Here we present the state of the art for LAB stress behavior. We describe the multitude of stresses that LAB are confronted with, and we present the experimental context used to study the stress responses of LAB, focusing on adaptation, habituation, and cross-protection as well as on self-induced multistress resistance in stationary phase, biofilms, and dormancy. We also consider stress responses at the population and single-cell levels. Subsequently, we concentrate on the stress defense mechanisms that have been reported to date, grouping them according to their direct participation in preserving cell energy, defending macromolecules, and protecting the cell envelope. Stress-induced responses of probiotic LAB and commensal/pathogenic LAB are highlighted separately due to the complexity of the peculiar multistress conditions to which these bacteria are subjected in their hosts. Induction of prophages under environmental stresses is then discussed. Finally, we present systems-based strategies to characterize the "stressome" of LAB and to engineer new food-related and probiotic LAB with improved stress tolerance.

Oxidative Stress

The ancestors of Escherichia coli and Salmonella ultimately evolved to thrive in air-saturated liquids, in which oxygen levels reach 210 μM at 37°C. However, in 1976 Brown and colleagues reported that some sensitivity persists: growth defects still become apparent when hyperoxia is imposed on cultures of E. coli. This residual vulnerability was important in that it raised the prospect that normal levels of oxygen might also injure bacteria, albeit at reduced rates that are not overtly toxic. The intent of this article is both to describe the threat that molecular oxygen poses for bacteria and to detail what we currently understand about the strategies by which E. coli and Salmonella defend themselves against it. E. coli mutants that lack either superoxide dismutases or catalases and peroxidases exhibit a variety of growth defects. These phenotypes constitute the best evidence that aerobic cells continually generate intracellular superoxide and hydrogen peroxide at potentially lethal doses. Superoxide has reduction potentials that allow it to serve in vitro as either a weak univalent reductant or a stronger univalent oxidant. The addition of micromolar hydrogen peroxide to lab media will immediately block the growth of most cells, and protracted exposure will result in the loss of viability. The need for inducible antioxidant systems seems especially obvious for enteric bacteria, which move quickly from the anaerobic gut to fully aerobic surface waters or even to ROS-perfused phagolysosomes. E. coli and Salmonella have provided two paradigmatic models of oxidative-stress responses: the SoxRS and OxyR systems.

Descending necrotizing mediastinitis associated with Lactobacillus plantarum

Background

Descending necrotizing mediastinitis (DNM), a severe infection with a high fatality rate, develops in mediastinal spaces due mainly to deep cervical abscesses. The majority of causative microbes of DNM are Streptococci and oral anaerobes. DNM associated with Lactobacillus-infection is rather rare.

Case presentation

A 69-year-old male with an unremarkable past medical history was referred to our hospital for surgical resection of advanced laryngeal cancer. Full examination revealed a neck abscess and DNM with a background of untreated diabetes mellitus. Initially, he was treated with meropenem. However, Lactobacillus plantarum was isolated from surgical drainage of a mediastinal abscess. Despite using antibiotics capable of eradicating all isolates with susceptibilities not differing significantly from those of the neck and mediastinal abscesses, we attributed DNM to the L. plantarum detected only in the mediastinal abscess. After DNM treatment, he underwent total pharyngolaryngectomy with bilateral neck dissection followed by reconstruction using free jejunum. He was discharged fully recovered.

Conclusion

We concluded that L. plantarum as the sole cause of the mediastinal abscess in the present case cannot be ruled out. As the number of immunocompromised patients increases, we should be cautious regarding this “familiar” microbe.

Enzyme Activities Affecting End Product Distribution by Lactobacillus plantarum in Response to Changes in pH and O(2)

Lactobacillus plantarum catabolic end products changed in response to environmental conditions. While lactate was always the major end product, acetate was produced in alkaline and aerobic environments. Acetoin levels decreased under alkaline conditions. Changes in acetoin dehydrogenase, acetate kinase, NADH oxidase, pyruvate oxidase, and acetate kinase activities correlated with changes in end product distribution.

Role of antioxidant enzymes in bacterial resistance to organic acids

Growth in aerobic environments has been shown to generate reactive oxygen species (ROS) and to cause oxidative stress in most organisms. Antioxidant enzymes (i.e., superoxide dismutases and hydroperoxidases) and DNA repair mechanisms provide protection against ROS. Acid stress has been shown to be associated with the induction of Mn superoxide dismutase (MnSOD) in Lactococcus lactis and Staphylococcus aureus. However, the relationship between acid stress and oxidative stress is not well understood. In the present study, we showed that mutations in the gene coding for MnSOD (sodA) increased the toxicity of lactic acid at pH 3.5 in Streptococcus thermophilus. The inclusion of the iron chelators 2,2'-dipyridyl (DIP), diethienetriamine-pentaacetic acid (DTPA), and O-phenanthroline (O-Phe) provided partial protection against 330 mM lactic acid at pH 3.5. The results suggested that acid stress triggers an iron-mediated oxidative stress that can be ameliorated by MnSOD and iron chelators. These findings were further validated in Escherichia coli strains lacking both MnSOD and iron SOD (FeSOD) but expressing a heterologous MnSOD from S. thermophilus. We also found that, in E. coli, FeSOD did not provide the same protection afforded by MnSOD and that hydroperoxidases are equally important in protecting the cells against acid stress. These findings may explain the ability of some microorganisms to survive better in acidified environments, as in acid foods, during fermentation and accumulation of lactic acid or during passage through the low pH of the stomach.

Involvement of the mannose phosphotransferase system of Lactobacillus plantarum WCFS1 in peroxide stress tolerance

A Lactobacillus plantarum strain with a deletion in the gene rpoN, encoding the alternative sigma factor 54 (sigma(54)), displayed a 100-fold-higher sensitivity to peroxide than its parental strain. This feature could be due to sigma(54)-dependent regulation of genes involved in the peroxide stress response. However, transcriptome analyses of the wild type and the mutant strain during peroxide exposure did not support such a role for sigma(54). Subsequent experiments revealed that the impaired expression of the mannose phosphotransferase system (PTS) operon in the rpoN mutant caused the observed increased peroxide sensitivity.

Improvement of Lactobacillus plantarum aerobic growth as directed by comprehensive transcriptome analysis

An aerobic Lactobacillus plantarum culture displayed growth stagnation during early growth. Transcriptome analysis revealed that resumption of growth after stagnation correlated with activation of CO(2)-producing pathways, suggesting that a limiting CO(2) concentration induced the stagnation. Analogously, increasing the CO(2) gas partial pressure during aerobic fermentation prevented the temporal growth stagnation.

Examination of Lactobacillus plantarum lactate metabolism side effects in relation to the modulation of aeration parameters

AIMS

The characterization of global aerobic metabolism of Lactobacillus plantarum LP652 under different aeration levels, in order to optimize acetate production kinetics and to suppress H2O2 toxicity.

METHODS AND RESULTS

Cultures of L. plantarum were grown on different aeration conditions. After sugar exhaustion and in the presence of oxygen, lactate was converted to acetate, H2O2 and carbon dioxide with concomitant ATP production. Physiological assays were performed at selected intervals in order to assess enzyme activity and vitality of the strain during lactic acid conversion. The maximal aerated condition led to fast lactate-to-acetate conversion kinetics between 8 and 12 h, but H2O2 immediately accumulated, thus affecting cell metabolism. Pyruvate oxidase activity was highly enhanced by oxygen tension and was responsible for H2O2 production after 12 h of culture, whereas lactate oxidase and NADH-dependent lactate dehydrogenase activities were not correlated to metabolite production. Limited NADH oxidase (NOX) and NADH peroxidase (NPR) activities were probably responsible for toxic H2O2 levels in over-aerated cultures.

CONCLUSION

Modulating initial airflow led to the maximal specific activity of NOX and NPR observed after 24 h of culture, thus promoting H2O2 destruction and strain vitality at the end of the process.

SIGNIFICANCE AND IMPACT OF THE STUDY

Optimal aeration conditions were determined to minimize H2O2 concentration level during growth on lactate.

Pyruvate:quinone oxidoreductase in Corynebacterium glutamicum: molecular analysis of the pqo gene, significance of the enzyme, and phylogenetic aspects

Corynebacterium glutamicum recently has been shown to possess pyruvate:quinone oxidoreductase (PQO), catalyzing the oxidative decarboxylation of pyruvate to acetate and CO2 with a quinone as the electron acceptor. Here, we analyze the expression of the C. glutamicum pqo gene, investigate the relevance of the PQO enzyme for growth and amino acid production, and perform phylogenetic studies. Expression analyses revealed that transcription of pqo is initiated 45 bp upstream of the translational start site and that it is organized in an operon together with genes encoding a putative metal-activated pyridoxal enzyme and a putative activator protein. Inactivation of the chromosomal pqo gene led to the absence of PQO activity; however, growth and amino acid production were not affected under either condition tested. Introduction of plasmid-bound pqo into a pyruvate dehydrogenase complex-negative C. glutamicum strain partially relieved the growth phenotype of this mutant, indicating that high PQO activity can compensate for the function of the pyruvate dehydrogenase complex. To investigate the distribution of PQO enzymes in prokaryotes and to clarify the relationship between PQO, pyruvate oxidase (POX), and acetohydroxy acid synthase enzymes, we compiled and analyzed the phylogeny of respective proteins deposited in public databases. The analyses revealed a wide distribution of PQOs among prokaryotes, corroborated the hypothesis of a common ancestry of the three enzymes, and led us to propose that the POX enzymes of Lactobacillales were derived from a PQO.

Expression of a heterologous manganese superoxide dismutase gene in intestinal lactobacilli provides protection against hydrogen peroxide toxicity

In living organisms, exposure to oxygen provokes oxidative stress. A widespread mechanism for protection against oxidative stress is provided by the antioxidant enzymes: superoxide dismutases (SODs) and hydroperoxidases. Generally, these enzymes are not present in Lactobacillus spp. In this study, we examined the potential advantages of providing a heterologous SOD to some of the intestinal lactobacilli. Thus, the gene encoding the manganese-containing SOD (sodA) was cloned from Streptococcus thermophilus AO54 and expressed in four intestinal lactobacilli. A 1.2-kb PCR product containing the sodA gene was cloned into the shuttle vector pTRK563, to yield pSodA, which was functionally expressed and complemented an Escherichia coli strain deficient in Mn and FeSODs. The plasmid, pSodA, was subsequently introduced and expressed in Lactobacillus gasseri NCK334, Lactobacillus johnsonii NCK89, Lactobacillus acidophilus NCK56, and Lactobacillus reuteri NCK932. Molecular and biochemical analyses confirmed the presence of the gene (sodA) and the expression of an active gene product (MnSOD) in these strains of lactobacilli. The specific activities of MnSOD were 6.7, 3.8, 5.8, and 60.7 U/mg of protein for L. gasseri, L. johnsonii, L. acidophilus, and L. reuteri, respectively. The expression of S. thermophilus MnSOD in L. gasseri and L. acidophilus provided protection against hydrogen peroxide stress. The data show that MnSOD protects cells against hydrogen peroxide by removing O(2)(.-) and preventing the redox cycling of iron. To our best knowledge, this is the first report of a sodA from S. thermophilus being expressed in other lactic acid bacteria.

Environmental stress responses in Lactobacillus: a review

Environmental stress responses in Lactobacillus, which have been investigated mainly by proteomics approaches, are reviewed. The physiological and molecular mechanisms of responses to heat, cold, acid, osmotic, oxygen, high pressure and starvation stresses are described. Specific examples of the repercussions of these effects in food processing are given. Molecular mechanisms of stress responses in lactobacilli and other bacteria are compared.

Characterization and functional analysis of the poxB gene, which encodes pyruvate oxidase in Lactobacillus plantarum

The pyruvate oxidase gene (poxB) from Lactobacillus plantarum Lp80 was cloned and characterized. Northern blot and primer extension analyses revealed that transcription of poxB is monocistronic and under the control of a vegetative promoter. poxB mRNA expression was strongly induced by aeration and was repressed by glucose. Moreover, Northern blotting performed at different stages of growth showed that poxB expression is maximal in the early stationary phase when glucose is exhausted. Primer extension and in vivo footprint analyses revealed that glucose repression of poxB is mediated by CcpA binding to the cre site identified in the promoter region. The functional role of the PoxB enzyme was studied by using gene overexpression and knockout in order to evaluate its implications for acetate production. Constitutive overproduction of PoxB in L. plantarum revealed the predominant role of pyruvate oxidase in the control of acetate production under aerobic conditions. The DeltapoxB mutant strain exhibited a moderate (20 to 25%) decrease in acetate production when it was grown on glucose as the carbon source, and residual pyruvate oxidase activity that was between 20 and 85% of the wild-type activity was observed with glucose limitation (0.2% glucose). In contrast, when the organism was grown on maltose, the poxB mutation resulted in a large (60 to 80%) decrease in acetate production. In agreement with the latter observation, the level of residual pyruvate oxidase activity with maltose limitation (0.2% maltose) was less than 10% of the wild-type level of activity.

Molecular characterization and functional analysis of the manganese-containing superoxide dismutase gene (sodA) from Streptococcus thermophilus AO54

This report describes the isolation, sequencing, and functional analysis of the sodA gene, encoding Mn-superoxide dismutase, from Streptococcus thermophilus AO54. The gene was found to encode a 201 amino acid polypeptide with 88 and 83% identity to SodA from Streptococcus mutans and Streptococcus agalacticae, respectively. Primer extension analysis revealed a transcriptional start site 27 nucleotides upstream of initiation codon. The gene was expressed in Escherichia coli and was able to rescue the growth of a sodAsodB mutant in a minimal-medium containing 10(-6)M paraquat. A sodA mutant of S. thermophilus was constructed and found to be more sensitive to aerobic growth than its parent strain. Supplementing the medium with MnCl(2) improved the growth of the mutant, only under microaerophilic conditions. The results suggest that sodA is essential for the aerobic growth of S. thermophilus. In the absence of functional SodA, manganese ions may provide partial protection against oxygen toxicity.

Hydrogen peroxide-forming NADH oxidase belonging to the peroxiredoxin oxidoreductase family: existence and physiological role in bacteria

Amphibacillus xylanus and Sporolactobacillus inulinus NADH oxidases belonging to the peroxiredoxin oxidoreductase family show extremely high peroxide reductase activity for hydrogen peroxide and alkyl hydroperoxides in the presence of the small disulfide redox protein, AhpC (peroxiredoxin). In order to investigate the distribution of this enzyme system in bacteria, 15 bacterial strains were selected from typical aerobic, facultatively anaerobic, and anaerobic bacteria. AhpC-linked alkyl hydroperoxide reductase activities were detected in most of the tested strains, and especially high activities were shown in six bacterial species that grow well under aerobic conditions, including aerobic bacteria (Alcaligenes faecalis and Bacillus licheniformis) and facultatively anaerobic bacteria (Amphibacillus xylanus, Sporolactobacillus inulinus, Escherichia coli, and Salmonella enterica serovar Typhimurium). In the absence of AhpC, the purified enzymes from A. xylanus and S. inulinus catalyze the NADH-linked reduction of oxygen to hydrogen peroxide. Similar activities were observed in the cell extracts from each of these six strains. The cell extract of B. licheniformis revealed the highest AhpC-linked alkyl hydroperoxide reductase activity in the four strains, with V(max) values for hydrogen peroxide and alkyl hydroperoxides being similar to those for the enzymes from A. xylanus and S. inulinus. Southern blot analysis of the three strains probed with the A. xylanus peroxiredoxin reductase gene revealed single strong bands, which are presumably derived from the individual peroxiredoxin reductase genes. Single bands were also revealed in other strains which show high AhpC-linked reductase activities, suggesting that the NADH oxidases belonging to the peroxiredoxin oxidoreductase family are widely distributed and possibly play an important role both in the peroxide-scavenging systems and in an effective regeneration system for NAD in aerobically growing bacteria.

Increased production of hydrogen peroxide by Lactobacillus delbrueckii subsp. bulgaricus upon aeration: involvement of an NADH oxidase in oxidative stress

The growth of Lactobacillus delbrueckii subsp. bulgaricus (L. delbrueckii subsp. bulgaricus) on lactose was altered upon aerating the cultures by agitation. Aeration caused the bacteria to enter early into stationary phase, thus reducing markedly the biomass production but without modifying the maximum growth rate. The early entry into stationary phase of aerated cultures was probably related to the accumulation of hydrogen peroxide in the medium. Indeed, the concentration of hydrogen peroxide in aerated cultures was two to three times higher than in unaerated ones. Also, a similar shift from exponential to stationary phase could be induced in unaerated cultures by adding increasing concentrations of hydrogen peroxide. A significant fraction of the hydrogen peroxide produced by L. delbrueckii subsp. bulgaricus originated from the reduction of molecular oxygen by NADH catalyzed by an NADH:H(2)O(2) oxidase. The specific activity of this NADH oxidase was the same in aerated and unaerated cultures, suggesting that the amount of this enzyme was not directly regulated by oxygen. Aeration did not change the homolactic character of lactose fermentation by L. delbrueckii subsp. bulgaricus and most of the NADH was reoxidized by lactate dehydrogenase with pyruvate. This indicated that NADH oxidase had no (or a very small) energetic role and could be involved in eliminating oxygen.

Isolation, oxygen sensitivity, and virulence of NADH oxidase mutants of the anaerobic spirochete Brachyspira (Serpulina) hyodysenteriae, etiologic agent of swine dysentery

Brachyspira (Serpulina) hyodysenteriae, the etiologic agent of swine dysentery, uses the enzyme NADH oxidase to consume oxygen. To investigate possible roles for NADH oxidase in the growth and virulence of this anaerobic spirochete, mutant strains deficient in oxidase activity were isolated and characterized. The cloned NADH oxidase gene (nox; GenBank accession no. U19610) on plasmid pER218 was inactivated by replacing 321 bp of coding sequence with either a gene for chloramphenicol resistance (cat) or a gene for kanamycin resistance (kan). The resulting plasmids, respectively, pCmDeltaNOX and pKmDeltaNOX, were used to transform wild-type B. hyodysenteriae B204 cells and generate the antibiotic-resistant strains Nox-Cm and Nox-Km. PCR and Southern hybridization analyses indicated that the chromosomal wild-type nox genes in these strains had been replaced, through allelic exchange, by the inactivated nox gene containing cat or kan. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western immunoblot analysis revealed that both nox mutant cell lysates were missing the 48-kDa Nox protein. Soluble NADH oxidase activity levels in cell lysates of Nox-Cm and Nox-Km were reduced 92 to 96% compared to the activity level in parent strain B204. In an aerotolerance test, cells of both nox mutants were at least 100-fold more sensitive to oxygen exposure than were cells of the wild-type parent strain B204. In swine experimental infections, both nox mutants were less virulent than strain B204 in that fewer animals were colonized by the mutant cells and infected animals displayed mild, transient signs of disease, with no deaths. These results provide evidence that NADH oxidase serves to protect B. hyodysenteriae cells against oxygen toxicity and that the enzyme, in that role, contributes to the pathogenic ability of the spirochete.

Weak light emission patterns from lactic acid bacteria

Distinct low level chemiluminescence patterns during aerobic growth of a selection of bacterial strains of the lactic acid group were recorded in on-line measurements. These patterns may be specific for the strain and the medium employed for cultivation. The patterns are oxygen-dependent and consist in the case of Enterococcus faecalis of three basic patterns, which reflect different mechanisms leading to both the generation and depletion of initiators of the chemiluminescence, particularly hydrogen peroxide and superoxide radical. The influence of catalase and superoxide dismutase on the patterns was examined. We could demonstrate the sensitivity of chemiluminescence measurements for the detection of both exogenous oxidative stress, which is imposed to the cells by reactive species formed in the medium, as well as endogenous oxidative stress, which is due to products of the cellular oxygen metabolism, the latter being often the reason for growth restriction.

Characterization of superoxide dismutase in Streptococcus thermophilus

Streptococcus thermophilus AO54 possesses a single manganese-containing superoxide dismutase (MnSOD). The enzyme was found to be insensitive to cyanide or to a modified H2O2 treatment. The enzyme is expressed in a growth-phase-dependent fashion, increasing three- to fourfold upon entry into stationary phase. The specific activity for MnSOD was the same under anaerobic or aerobic conditions and was not induced by the presence of paraquat under aerobic conditions.

13C nuclear magnetic resonance analysis of glucose and citrate end products in an ldhL-ldhD double-knockout strain of Lactobacillus plantarum

We have examined the metabolic consequences of knocking out the two ldh genes in Lactobacillus plantarum using 13C nuclear magnetic resonance. Unlike its wild-type isogenic progenitor, which produced lactate as the major metabolite under all conditions tested, ldh null strain TF103 mainly produced acetoin. A variety of secondary end products were also found, including organic acids (acetate, succinate, pyruvate, and lactate), ethanol, 2,3-butanediol, and mannitol.

Catabolic pathway for aerobic degradation of lactate by Actinomyces naeslundii

The aerobic metabolism of lactate by oral Actinomyces was studied. Six of 7 strains of Actinomyces naeslundii increased their growth in the presence of lactate under aerobic conditions. Washed cells grown on lactate aerobically degraded lactate and pyruvate to acetate with a concomitant consumption of oxygen. In the presence of catalase, the molar ratios of oxygen consumed to acetate produced were 1 for lactate degradation and 0.5 for pyruvate degradation. The enzymatic activities found in cell extracts revealed that lactate could be converted to pyruvate by NAD-independent lactate dehydrogenase (iLDH) and further to acetyl CoA by pyruvate dehydrogenase (PDH). The acetyl CoA formed could be metabolized into acetate by phosphotransacetylase (PTA) and acetate kinase (AK) with the formation of ATP. These results indicate that A. naeslundii metabolizes lactate into acetate by the sequential enzymatic reactions iLDH, PDH, PTA and AK and that hydrogens produced by iLDH and PDH are transferred to oxygen. The activity of lactate degradation and oxygen consumption may modify the environmental conditions of dental plaque.

Crystal structure of NADH oxidase from Thermus thermophilus

The crystal structures of the flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) containing isoforms of NADH oxidase from Thermus thermophilus have been determined by isomorphous and molecular replacement and refined to 2.3 A and 1.6 A resolution with R-values of 18.5% and 18.6% respectively. The structure of the homodimeric enzyme consists of a central 4-stranded antiparallel beta-sheet covered by helices, a more flexible domain formed by two helices, and a C-terminal excursion connecting the subunits. The active sites are located in a deep cleft between the subunits. The binding site of the flavin cofactor lacks the common nucleotide binding fold and is different from the FMN binding site found in flavodoxins.

Anticarcinogenic, hypocholesterolemic, and antagonistic activities of Lactobacillus acidophilus

Lactobacillus acidophilus is considered to possess health-promoting attributes. These include anticarcinogenic and hypocholesterolemic properties and antagonistic action against intestinal and food-born pathogens. L. acidophilus can also survive the hostile environment and establish in the complex ecosystem of the gastrointestinal tract. Therefore, the beneficial effects of ingesting L. acidophilus accrue over a longer period than those organisms that cannot colonize the gut. However, the exact mechanisms of these attributes are not known. Presumably, the anticarcinogenic activity may be attributed to production of compounds and/or conditions that inhibit the proliferation of tumor cells, suppression of microorganisms that convert procarcinogens to carcinogens, and degradation of carcinogens formed. They hypocholesterolemic effect is probably exerted by inhibition of 3-hydroxy-3-methylglutaryl CoA reductase, which is a rate-limiting enzyme in endogenous cholesterol biosynthesis in the body and by promoting the excretion of dietary cholesterol in feces as a result of coprecipitation in the presence of deconjugated bile acids in the intestine and/or adsorption by the organisms. The antagonistic effect against pathogens and other organisms is possibly mediated by competition for nutrients and adhesion sites, formation of metabolites such as organic acids, hydrogen peroxide, and production of antibiotic-like compounds and bacteriocins.

Regulation of acetic acid production by homo- and heterofermentative lactobacilli in whole-wheat sour-doughs

The efficiency of sour-dough as a possible preservative agent of microbial spoilage of bread depends on its acetic acid content. As a secondary metabolite of sugar fermentation by lactic acid bacteria, acetic acid may be promoted in the presence of O2 or H+ acceptors. This paper studies the influence of O2 and high fructose content products (pure sugar, invert sugar, fructose syrup) addition on acetic acid production by hetero- (Lactobacillus brevis 25a, B-21, L-62; L. sanfrancisco L-99) and homofermentative (L. plantarum B-39) lactobacilli in whole-wheat sour-doughs [280 and 250 dough yield (DY)]. The pH and total titratable acidity (TTA) of sour-doughs after 44 h fermentation varied with DY and strain. As expected, the addition of O2 promoted greater increases in TTA with heterofermentative lactobacilli (15-42%) than with L. plantarum (15%). Fructose addition was only effective for heterofermentative strains, but the overall effects were smaller than those observed for oxygenation. The ability of lactobacilli to produce acetic acid in sour-doughs without treatment varied from 0.16 g/100 g flour at 44 h (B-39, 280, 350 DY) to 0.47-0.65% (L-62, 280, 350 DY). The production of acetic acid was positively promoted by all treatments. Oxygenation was again the most effective way of inducing acetic acid production; increases ranged from 54% (B-21) to 269% (L-99, 350 DY). The addition of H+ acceptors had variable effects.(ABSTRACT TRUNCATED AT 250 WORDS)

A flavoprotein functional as NADH oxidase from Amphibacillus xylanus Ep01: purification and characterization of the enzyme and structural analysis of its gene

Amphibacillus xylanus Ep01, a facultative anaerobe we recently isolated, shows rapid aerobic growth even though it lacks a respiratory pathway. Thus, the oxidative consumption of NADH, produced during glycolysis and pyruvate oxidation, should be especially important for maintenance of intracellular redox balance in this bacterium. We purified a flavoprotein functional as NADH oxidase from aerobically growing A. xylanus Ep01. The A. xylanus enzyme is a homotetramer composed of a subunit (M(r) 56,000) containing 1 mol of flavin adenine dinucleotide. This enzyme catalyzes the reduction of oxygen to hydrogen peroxide with beta-NADH as the preferred electron donor and exhibits no activity with NADPH. The flavoprotein gene of A. xylanus Ep01 was cloned by using a specific antibody. The amino acid sequence of 509 residues, deduced from the nucleotide sequence, showed 51.2 and 72.5% identities to the amino acid sequences of alkyl hydroperoxide reductase from Salmonella typhimurium and NADH dehydrogenase from alkalophilic Bacillus sp. strain YN-1, respectively. Bacillus spp. have a respiratory chain and grow well under aerobic conditions. In contrast, Amphibacillus spp., having no respiratory chain, grow equally well under both aerobic and anaerobic conditions, which distinguishes these two genera. Salmonella spp., which are gram-negative bacteria, are taxonomically distant from gram-positive bacteria such as Bacillus spp. and Amphibacillus spp. The above findings, however, suggest that the flavoprotein functional as NADH oxidase, the alkyl hydroperoxide reductase, and the NADH dehydrogenase diverged recently, with only small changes leading to their functional differences.

Oxygen-dependent lactate utilization by Actinomyces viscosus and Actinomyces naeslundii

Actinomyces viscosus and Actinomyces naeslundii were grown in chemostat cultures with glucose or lactate as the sole sources of energy. Growth on lactate was dependent on oxygen. Lactate was oxidised partly to acetic acid. As judged from the low carbon recoveries in acidic degradation products, it is concluded that a substantial part of the lactate was oxidised to carbon dioxide. Assuming that 1 ATP is generated in the transfer of an electron pair to oxygen, YATP values of 10-11 were calculated from the molar growth yield on lactate and product formation. Although all cell 3 test strains oxidised lactate, one strain could not grow on lactate as the sole source of energy. The rate of oxygen uptake with lactate as substrate was higher for cells grown aerobically than of cells grown anaerobically, indicating that lactate oxidation was induced by oxygen. It is reasonable to assume that lactate oxidation is mediated either by lactate dehydrogenase or lactate oxidase, but the pathway in Actinomyces sp. is not yet known. Lactate consumption may be an important trait of Actinomyces sp. that live in an environment limited in energy sources for most of the time.

Glucose metabolism and NADH recycling by Treponema hyodysenteriae, the agent of swine dysentery

Glucose metabolism and the mechanisms of NADH oxidation by Treponema hyodysenteriae were studied. Under an N2 atmosphere, washed cell suspensions of the spirochete consumed glucose and produced acetate, butyrate, H2, and CO2. Approximately twice as much H2 as CO2 was produced. Determinations of radioactivity in products of [14C]glucose and [14C]pyruvate metabolism and analyses of enzyme activities in cell lysates revealed that glucose was catabolized to pyruvate via the Embden-Meyerhof-Parnas pathway. The results of pyruvate exchange reactions with NaH14CO3 and Na14COOH demonstrated that pyruvate was converted to acetyl coenzyme A (acetyl-CoA), H2, and CO2 by a clostridium-type phosphoroclastic mechanism. NADH:ferredoxin oxidoreductase and hydrogenase activities were present in cell lysates and produced H2 from NADH oxidation. Phosphotransacetylase and acetate kinase catalyzed the formation of acetate from acetyl-CoA. Butyrate was formed from acetyl-CoA via a pathway that involved 3-hydroxybutyryl-coenzyme A (CoA) dehydrogenase, butyryl-CoA dehydrogenase, and butyryl-CoA transferase. T. hyodysenteriae cell suspensions generated less H2 and butyrate under 10% O2-90% N2 than under 100% N2. Cell lysates contained NADH oxidase, NADH peroxidase, and superoxide dismutase activities. These findings indicated there are three major mechanisms that T. hyodysenteriae cells use to recycle NADH generated from the Embden-Meyerhof-Parnas pathway--enzymes in the pathway from acetyl-CoA to butyrate, NADH:ferredoxin oxidoreductase, and NADH oxidase. Versatility in methods of NADH oxidation and an ability to metabolize oxygen could benefit T. hyodysenteriae cells in the colonization of tissues of the swine large bowel.

Fatty acid dependent hydrogen peroxide production in Lactobacillus

Lactobacillus leichmanii growing in complex medium supplemented with decanoic acid accumulated high concentrations of hydrogen peroxide in the culture. The H2O2-generating system was specifically induced by one of the saturated fatty acids from 4:0 to 16:0 or oleic acid. The induction of this system was associated with the presence of a fatty acyl-CoA-dependent H2O2-generating activity in the cell-free extracts. This activity is shown for the first time in a procaryote organism.

Manganese: its acquisition by and function in the lactic acid bacteria

The transition metal manganese is considered to be a minor micronutrient in both pro- and eukaryotes, usually being required from the environment at subnanomolar levels. Until recently, Mn was only known to function in cells as a cofactor for a few enzymatic reactions. A notable exception has been reported in many lactic acid bacterial species which require micromolar medium Mn levels for growth and contain up to 35 mM Mn. These high Mn concentrations are accompanied by the near or complete absence of intracellular iron and superoxide dismutase (SOD). Lacking hemes, Lactobacillus plantarum and related species contain a unique Mn-cofactored catalase as well as millimolar Mn(II) in a nonenzymic complex performing the function of the micromolar superoxide dismutase found in most other aerotolerant cells. The high Mn(II) levels are accumulated via an efficient active transport system and are stored intracellularly in a high molecular weight complex. Study of Lactobacillus plantarum has provided an interesting example of the substitution of Mn for Fe in several of the biological roles of Fe, an alternative mechanism of aerotolerance, and a better understanding of the unique biochemistry of the lactic acid bacteria.

Lactate metabolism by pediococci isolated from cheese

Pediococcus pentosaceus is commonly found among the adventitious microflora of Cheddar cheese. When this organism was incubated with L-(+)-lactate under anaerobic conditions, L-(+)-lactate was rapidly converted to D-(-)-lactate until racemic (DL) lactate was present. Under aerobic conditions this initial reaction was followed by a slower reaction resulting in the use of both lactate isomers and in the production of acetate and CO2. With intact cells the lactate oxidation system had an optimum pH of 5 to 6, depending on the initial lactate concentration. Cells grown anaerobically possessed lactate-oxidizing activity which increased two- to fourfold as sugar was exhausted from the medium. Aerobic growth further increased specific activities. Cheddar cheese was made with the deliberate addition of P. pentosaceus. When the resulting cheese was grated to expose a large surface area to O2, lactate was converted to acetate at a rate which depended on the density of pediococci in the cheese. The lactate oxidation system remained active in cheese which had been ripened for 6 months.

Oxygen dependent lactate utilization by Lactobacillus plantarum

Lactobacillus plantarum P5 grew aerobically in rich media at the expense of lactate; no growth was observed in the absence of aeration. The oxygen-dependent growth was accompanied by the conversion of lactate to acetate which accumulated in the growth medium. Utilization of oxygen with lactate as substrate was observed in buffered suspensions of washed whole cells and in cell-free extracts. A pathway which accounts for the generation of adenosine triphosphate during aerobic metabolism of lactate to acetate via pyruvate and acetyl phosphate is proposed. Each of the enzyme activities involved, nicotinamide adenine dinucleotide independent lactic dehydrogenase, nicotinamide adenine dinucleotide dependent lactic dehydrogenase, pyruvate oxidase, acetate kinase and NADH oxidase were demonstrated in cell-free extracts. The production of pyruvate, acetyl phosphate and acetate was demonstrated using cell-free extracts and cofactors for the enzymes of the proposed pathway.

Physiological role of pyruvate oxidase in the aerobic metabolism of Lactobacillus plantarum

Under aerobic growth conditions Lactobacillus plantarum produced acetic acid in addition to lactic acid. It was found that lactic acid was predominantly produced at first, and then when the carbohydrate was nearly exhausted, lactic acid was metabolized further to acetic acid. The most likely enzyme involved in the aerobic metabolism of L. plantarum is pyruvate oxidase. Its activity is enhanced in the presence of oxygen and is reduced in the presence of glucose. The specific activity of pyruvate oxidase is highest at the beginning of the stationary-growth phase, where a strong increase in acetic acid production was also observed.

Purification and biochemical characterization of pyruvate oxidase from Lactobacillus plantarum

Pyruvate oxidase (EC 1.2.3.3) was isolated and characterized from Lactobacillus plantarum. The enzyme catalyzes the oxidative decarboxylation of pyruvate in the presence of phosphate and oxygen, yielding acetyl phosphate, carbon dioxide, and hydrogen peroxide. This pyruvate oxidase is a flavoprotein, with the relatively tightly bound cofactors flavin adenine dinucleotide, thiamine pyrophosphate, and a divalent metal ion, with Mn2+ being the most effective. The enzyme is only slightly inhibited by EDTA, implying that the enzyme-bound metal ion is poorly accessible to EDTA. Only under relatively drastic conditions, such as acid ammonium sulfate precipitation, could a colorless and entirely inactive apoenzyme be obtained. A partial reactivation of the enzyme was only possible by the combined addition of flavin adenine dinucleotide, thiamine pyrophosphate, and MnSO4. The enzyme has a molecular weight of ca. 260,000 and consists of four subunits with apparently identical molecular weights of 68,000. For catalytic activity the optimum pH is 5.7, and the optimum temperature is 30 degrees C. The Km values for pyruvate, phosphate, and arsenate are 0.4, 2.3, and 1.2 mM, respectively. The substrate specificity revealed that the enzyme reacts also with certain aldehydes and that phosphate can be replaced by arsenate. In addition to oxygen, several artificial compounds can function as electron acceptors.

Correlation of oxygen utilization and hydrogen peroxide accumulation with oxygen induced enzymes in Lactobacillus plantarum cultures

Two strains of Lactobacillus plantarum accumulated H2O2 when grown aerobically in a complex glucose based medium. The H2O2 accumulation did not occur immediately on exposure of the culture to O2 but was delayed for a time which, in the case of one strain, was dependent on the amount of inoculum used to seed the culture. The accumulation was always preceded by an increase in the rate of O2 utilization by the cultures. The latter coincided approximately with an increase in specific activity of NADH oxidase, pyruvate oxidase and NADH peroxidase. H2O2 was not a product of NADH oxidase in vitro but was formed in substantial quantities from O2 during oxidation of pyruvate. The three enzymes were induced by O2 and H2O2; the induction of NADH oxidase responded to lower levels of O2 (but not of H2O2) than the pyruvate oxidase or the NADH peroxidase.