Contribution of NADH oxidase to aerobic metabolism of Streptococcus pyogenes

Roles of flavoprotein oxidase and the exogenous heme- and quinone-dependent respiratory chain in lactic acid bacteria

Lactic acid bacteria (LAB) are a type of bacteria that convert carbohydrates into lactate through fermentation metabolism. While LAB mainly acquire energy through this anaerobic process, they also have oxygen-consuming systems, one of which is flavoprotein oxidase and the other is exogenous heme- or heme- and quinone-dependent respiratory metabolism. Over the past two decades, research has contributed to the understanding of the roles of these oxidase machineries, confirming their suspected roles and uncovering novel functions. This review presents the roles of these oxidase machineries, which are anticipated to be critical for the future applications of LAB in industry and comprehending the virulence of pathogenic streptococci.

Mated-Atom Nanozymes with Efficient Assisted NAD+ Replenishment for Skin Regeneration

Excessive accumulation of reduced nicotinamide adenine dinucleotide (NADH) within biological organisms is closely associated with many diseases. It remains a challenge to efficiently convert superfluous and detrimental NADH to NAD+. NADH oxidase (NOX) is a crucial oxidoreductase that catalyzes the oxidation of NADH to NAD+. Herein, M1M2 (Mi=V/Mn/Fe/Co/Cu/Mo/Rh/Ru/Pd, i = 1 or 2) mated-atom nanozymes (MANs) are designed by mimicking natural enzymes with polymetallic active centers. Excitingly, RhCo MAN possesses excellent and sustainable NOX-like activity, with Km-NADH (16.11 μM) being lower than that of NOX-mimics reported so far. Thus, RhCo MAN can significantly promote the regeneration of NAD+ and regulate macrophage polarization toward the M2 phenotype through down-regulation of TLR4 expression, which may help to recover skin regeneration. However, RhRu MAN with peroxidase-like activity and RhMn MAN with superoxide dismutase-like activity exhibit little modulating effects on eczema. This work provides a new strategy to inhibit skin inflammation and promote skin regeneration.

Interplay between group A Streptococcus and host innate immune responses

SUMMARYGroup A Streptococcus (GAS), also known as Streptococcus pyogenes, is a clinically well-adapted human pathogen that harbors rich virulence determinants contributing to a broad spectrum of diseases. GAS is capable of invading epithelial, endothelial, and professional phagocytic cells while evading host innate immune responses, including phagocytosis, selective autophagy, light chain 3-associated phagocytosis, and inflammation. However, without a more complete understanding of the different ways invasive GAS infections develop, it is difficult to appreciate how GAS survives and multiplies in host cells that have interactive immune networks. This review article attempts to provide an overview of the behaviors and mechanisms that allow pathogenic GAS to invade cells, along with the strategies that host cells practice to constrain GAS infection. We highlight the counteractions taken by GAS to apply virulence factors such as streptolysin O, nicotinamide-adenine dinucleotidase, and streptococcal pyrogenic exotoxin B as a hindrance to host innate immune responses.

Strategies to enhance stress tolerance in lactic acid bacteria across diverse stress conditions

Lactic acid bacteria (LAB) hold significant importance in diverse fields, including food technology, industrial biotechnology, and medicine. As basic components of starter cultures, probiotics, immunomodulators, and live vaccines, LAB cells resist a variety of stressors, including temperature fluctuations, osmotic and pH shocks, exposure to oxidants and ultraviolet radiation, substrate deprivation, mechanical damage, and more. To stay alive in these adversities, LAB employ a wide range of stress response strategies supported by various mechanisms, for example rearrangement of metabolism, expression of specialized biomolecules (e.g., chaperones and antioxidants), exopolysaccharide synthesis, and complex repair and regulatory systems. LAB can coordinate responses to various stressors using global regulators. In this review, we summarize current knowledge about stress response strategies used by LAB and consider mechanisms of response to specific stressful factors, supported by illustrative examples. In addition, we discuss technical approaches to increase the stress resistance of LAB, including pre-adaptation, genetic modification of strains, and adjustment of cultivation conditions. A critical analysis of the recent findings in this field augments comprehension of stress tolerance mechanisms in LAB, paving the way for prospective research directions with implications in fundamental and practical areas.

Colonization of biofilm in wastewater treatment: A review

The attachment and colonization process of microorganisms on a carrier is an interdisciplinary research field. Through a series of physical, chemical, and biological actions, the microorganisms can eventually reproduce on the carrier. This article introduces biofilm start-up and its applications, and explores the current issues to look forward to future development directions. Firstly, the mechanism of microbial film formation is analyzed from the microbial community colonization and reproduction process. Secondly, when analyzing the factors influencing microbial membrane formation, the effect of microbial properties (e.g., genes, proteins, lipids) and external conditions (i.e., carrier, operating environment, and regulation mechanism among microbial communities) were discussed in depth. Aimed at exploring the mechanisms and influencing factors of biofilm start-up, this article proposes the application measures to strengthen this process. Finally, the problems encountered and the future development direction of the technology are analyzed and prospected.

Survival of Group A Streptococcus (GAS) is Enhanced Under Desiccated Culture Conditions

Streptococcus pyogenes or Group A Streptococcus (GAS) infections are the leading cause of bacterial tonsillopharyngitis. The bacterium can survive and persist within the human host for a long time as it is observed in up to 40% of the population who are considered as carriers. Recurrent tonsillopharyngitis is a particular problem in children which is caused either by relapses due to failed bacterial clearance or by reinfection. A prolonged survival in tonsillar crypts or on inanimate surfaces might be sources for reinfection. We therefore examined 64 clinical GAS isolates from children with tonsillopharyngitis for their long-term survival under either liquid or desiccated culture conditions. After 6 weeks, the overall GAS survival rate was 400-fold increased under desiccated culture conditions compared to liquid culture conditions, but varied depending on the emm-type between 20-fold (emm4) and 14000-fold (emm3). The survival rates of isolates from emm75 were significantly lower which is probably due to their production of hydrogen peroxide up to fatal doses. No hydrogen peroxide production could be detected for other emm-types. Furthermore, 11 isolates from patients with recurrent tonsillopharyngitis were compared to isolates of the same emm-type from patients with single episodes of tonsillopharyngitis. A significant elevated pH value and an increased survival rate for isolates from patients with recurrent infections were observed. In conclusion, significant differences in long-term survival of different GAS isolates as well as survival under desiccated culture conditions might contribute to both failed bacterial clearance and reinfection in patients with recurrent tonsillopharyngitis.

Tissue Tropism in Streptococcal Infection: Wild-Type M1T1 Group A Streptococcus Is Efficiently Cleared by Neutrophils Using an NADPH Oxidase-Dependent Mechanism in the Lung but Not in the Skin

Group A Streptococcus (GAS) commonly causes pharyngitis and skin infections. Little is known why streptococcal pharyngitis usually does not lead to pneumonia and why the skin is a favorite niche for GAS. To partially address these questions, the effectiveness of neutrophils in clearing wild-type (wt) M1T1 GAS strain MGAS2221 from the lung and from the skin was examined in murine models of intratracheal pneumonia and subcutaneous infection. Ninety-nine point seven percent of the MGAS2221 inoculum was cleared from the lungs of C57BL/6J mice at 24 h after inoculation, while there was no MGAS2221 clearance from skin infection sites. The bronchial termini had robust neutrophil infiltration, and depletion of neutrophils abolished MGAS2221 clearance from the lung. Phagocyte NADPH oxidase but not myeloperoxidase was required for MGAS2221 clearance. Thus, wt M1T1 GAS can be cleared by neutrophils using an NADPH oxidase-dependent mechanism in the lung. MGAS2221 induced robust neutrophil infiltration at the edge of skin infection sites and throughout infection sites at 24 h and 48 h after inoculation, respectively. Neutrophils within MGAS2221 infection sites had no nuclear staining. Skin infection sites of streptolysin S-deficient MGAS2221 ΔsagA were full of neutrophils with nuclear staining, whereas MGAS2221 ΔsagA infection was not cleared. Gp91^phox knockout (KO) and control mice had similar GAS numbers at skin infection sites and similar abilities to select SpeB activity-negative (SpeB^A-) variants. These results indicate that phagocyte NADPH oxidase-mediated GAS killing is compromised in the skin. Our findings support a model for GAS skin tropism in which GAS generates an anoxic niche to evade phagocyte NADPH oxidase-mediated clearance.

Microtiter Screening Reveals Oxygen-Dependent Antimicrobial Activity of Natural Products Against Mastitis-Causing Bacteria

In this study we investigated the influence of oxygen availability on a phenotypic microtiter screen to identify new, natural product inhibitors of growth for the bovine mastitis-causing microorganisms; Streptococcus uberis, Staphylococcus aureus, and Escherichia coli. Mastitis is a common disease in dairy cattle worldwide and is a major cause of reduced milk yield and antibiotic usage in dairy herds. Prevention of bovine mastitis commonly relies on the application of teat disinfectants that contain either iodine or chlorhexidine. These compounds are used extensively in human clinical settings and increased tolerance to chlorhexidine has been reported in both Gram-positive and Gram-negative microorganisms. As such new, non-human use alternatives are required for the agricultural industry. Our screening was conducted under normoxic (20% oxygen) and hypoxic (<1% oxygen) conditions to mimic the conditions on teat skin and within the mammary gland respectively, against two natural compound libraries. No compounds inhibited E. coli under either oxygen condition. Against the Gram-positive microorganisms, 12 inhibitory compounds were identified under normoxic conditions, and 10 under hypoxic conditions. Data revealed a clear oxygen-dependency amongst compounds inhibiting growth, with only partial overlap between oxygen conditions. The oxygen-dependent inhibitory activity of a naturally occurring quinone, β-lapachone, against S. uberis was subsequently investigated and we demonstrated that this compound is only active under normoxic conditions with a minimum inhibitory concentration and minimum bactericidal concentration of 32 μM and kills via a reactive oxygen species-dependent mechanism as has been demonstrated in other microorganisms. These results demonstrate the importance of considering oxygen-availability in high-throughput inhibitor discovery.

Energy metabolism in anaerobic eukaryotes and Earth's late oxygenation

Eukaryotes arose about 1.6 billion years ago, at a time when oxygen levels were still very low on Earth, both in the atmosphere and in the ocean. According to newer geochemical data, oxygen rose to approximately its present atmospheric levels very late in evolution, perhaps as late as the origin of land plants (only about 450 million years ago). It is therefore natural that many lineages of eukaryotes harbor, and use, enzymes for oxygen-independent energy metabolism. This paper provides a concise overview of anaerobic energy metabolism in eukaryotes with a focus on anaerobic energy metabolism in mitochondria. We also address the widespread assumption that oxygen improves the overall energetic state of a cell. While it is true that ATP yield from glucose or amino acids is increased in the presence of oxygen, it is also true that the synthesis of biomass costs thirteen times more energy per cell in the presence of oxygen than in anoxic conditions. This is because in the reaction of cellular biomass with O2, the equilibrium lies very far on the side of CO2. The absence of oxygen offers energetic benefits of the same magnitude as the presence of oxygen. Anaerobic and low oxygen environments are ancient. During evolution, some eukaryotes have specialized to life in permanently oxic environments (life on land), other eukaryotes have remained specialized to low oxygen habitats. We suggest that the Km of mitochondrial cytochrome c oxidase of 0.1-10 μM for O2, which corresponds to about 0.04%-4% (avg. 0.4%) of present atmospheric O2 levels, reflects environmental O2 concentrations that existed at the time that the eukaryotes arose.

A Host Proteome Atlas of Streptococcus pyogenes Infection

Multiplex quantitative proteomics analysis of mice infected with Group A Streptococcus reveals organ-specific biomarkers of infection.

Comparative Analysis of Listeria monocytogenes Plasmids and Expression Levels of Plasmid-Encoded Genes during Growth under Salt and Acid Stress Conditions

Listeria monocytogenes strains are known to harbour plasmids that confer resistance to sanitizers, heavy metals, and antibiotics; however, very little research has been conducted into how plasmids may influence L. monocytogenes’ ability to tolerate food-related stresses. To investigate this, a library (n = 93) of L. monocytogenes plasmid sequences were compared. Plasmid sequences were divided into two groups (G1 and G2) based on a repA phylogeny. Twenty-six unique plasmid types were observed, with 13 belonging to each of the two repA-based groups. G1 plasmids were significantly (p < 0.05) smaller than G2 plasmids but contained a larger diversity of genes. The most prevalent G1 plasmid (57,083 bp) was observed in 26 strains from both Switzerland and Canada and a variety of serotypes. Quantitative PCR (qPCR) revealed a >2-fold induction of plasmid-contained genes encoding an NADH peroxidase, cadmium ATPase, multicopper oxidase, and a ClpL chaperone protein during growth under salt (6% NaCl) and acid conditions (pH 5) and ProW, an osmolyte transporter, under salt stress conditions. No differences in salt and acid tolerance were observed between plasmid-cured and wildtype strains. This work highlights the abundance of specific plasmid types among food-related L. monocytogenes strains, the unique characteristics of G1 and G2 plasmids, and the possible contributions of plasmids to L. monocytogenes tolerance to food-related stresses.

Plasmids contribute to food processing environment-associated stress survival in three Listeria monocytogenes ST121, ST8, and ST5 strains

Listeria monocytogenes is a food-borne pathogen responsible for the disease listeriosis and is commonly isolated from food and food production facilities. Many L. monocytogenes strains contain plasmids, though the contributions of plasmids to survival in food production environments are unknown. Three L. monocytogenes ST5, ST8, and ST121 strains containing plasmids, which harbor putative stress response genes, were cured of their plasmids. Wildtype (WT) and plasmid-cured strains were exposed to disinfectant, oxidative, heat, acid, or salt stress. After stress exposure, cells were plated for colony forming unit (CFU) counts to determine survivors. L. monocytogenes WT strains exposed to 0.01% (vol/vol) H₂O₂, 1% (vol/vol) lactic acid, and 15% (wt/vol) NaCl, pH 5 showed significantly higher counts of survivors compared to the plasmid-cured strains. The number of survivors for the ST5 WT strain exposed to 10 μg/mL benzalkonium chloride (BC) was significantly higher than in the plasmid-cured strain. The ST8 and ST5 strains were exposed to elevated temperature (50° and 55 °C respectively); only the ST5 WT strain had significantly higher numbers of survivors than the plasmid-cured strains. Our data revealed that L. monocytogenes ST5, ST8, and ST121 plasmids contribute to tolerance against elevated temperature, salinity, acidic environments, oxidative stress and disinfectants.

Transcriptome and Proteome of Fish-Pathogenic Streptococcus agalactiae Are Modulated by Temperature

Streptococcus agalactiae is one of the most important pathogens associated with streptococcosis outbreaks in Nile tilapia farms worldwide. High water temperature (above 27°C) has been described as a predisposing factor for the disease in fish. At low temperatures (below 25°C), fish mortalities are not usually observed in farms. Temperature variation can modulate the expression of genes and proteins involved in metabolism, adaptation, and bacterial pathogenicity, thus increasing or decreasing the ability to infect the host. This study aimed to evaluate the transcriptome and proteome of a fish-pathogenic S. agalactiae strain SA53 subjected to in vitro growth at different temperatures using a microarray and label-free shotgun LC-HDMS^E approach. Biological triplicates of isolates were cultured in BHIT broth at 22 or 32°C for RNA and protein isolation and submitted for transcriptomic and proteomic analyses. In total, 1,730 transcripts were identified in SA53, with 107 genes being differentially expressed between the temperatures evaluated. A higher number of genes related to metabolism, mainly from the phosphotransferase system (PTS) and ATP-binding cassette (ABC) transport system, were upregulated at 32°C. In the proteome analysis, 1,046 proteins were identified in SA53, of which 81 were differentially regulated between 22 and 32°C. Proteins involved in defense mechanisms, lipid transport and metabolism, and nucleotide transport and metabolism were upregulated at 32°C. A higher number of interactions were observed in proteins involved in nucleotide transport and metabolism. We observed a low correlation between the transcriptome and proteome datasets. Our study indicates that the transcriptome and proteome of a fish-adapted S. agalactiae strain are modulated by temperature, particularly showing differential expression of genes/proteins involved in metabolism, virulence factors, and adaptation.

Defining Host Responses during Systemic Bacterial Infection through Construction of a Murine Organ Proteome Atlas

Group A Streptococcus (GAS) remains one of the top 10 deadliest human pathogens worldwide despite its sensitivity to penicillin. Although the most common GAS infection is pharyngitis (strep throat), it also causes life-threatening systemic infections. A series of complex networks between host and pathogen drive invasive infections, which have not been comprehensively mapped. Attempting to map these interactions, we examined organ-level protein dynamics using a mouse model of systemic GAS infection. We quantified over 11,000 proteins, defining organ-specific markers for all analyzed tissues. From this analysis, an atlas of dynamically regulated proteins and pathways was constructed. Through statistical methods, we narrowed organ-specific markers of infection to 34 from the defined atlas. We show these markers are trackable in blood of infected mice, and a subset has been observed in plasma samples from GAS-infected clinical patients. This proteomics-based strategy provides insight into host defense responses, establishes potentially useful targets for therapeutic intervention, and presents biomarkers for determining affected organs during bacterial infection.

Acid Stress Response Mechanisms of Group B Streptococci

Group B streptococcus (GBS) is a leading cause of neonatal mortality and morbidity in the United States and Europe. It is part of the vaginal microbiota in up to 30% of pregnant women and can be passed on to the newborn through perinatal transmission. GBS has the ability to survive in multiple different host niches. The pathophysiology of this bacterium reveals an outstanding ability to withstand varying pH fluctuations of the surrounding environments inside the human host. GBS host pathogen interations include colonization of the acidic vaginal mucosa, invasion of the neutral human blood or amniotic fluid, breaching of the blood brain barrier as well as survival within the acidic phagolysosomal compartment of macrophages. However, investigations on GBS responses to acid stress are limited. Technologies, such as whole genome sequencing, genome-wide transcription and proteome mapping facilitate large scale identification of genes and proteins. Mechanisms enabling GBS to cope with acid stress have mainly been studied through these techniques and are summarized in the current review

Transition Metal Homeostasis in Streptococcus pyogenes and Streptococcus pneumoniae

Trace metals such as Fe, Mn, Zn and Cu are essential for various biological functions including proper innate immune function. The host immune system has complicated and coordinated mechanisms in place to either starve and/or overload invading pathogens with various metals to combat the infection. Here, we discuss the roles of Fe, Mn and Zn in terms of nutritional immunity, and also the roles of Cu and Zn in metal overload in relation to the physiology and pathogenesis of two human streptococcal species, Streptococcus pneumoniae and Streptococcus pyogenes. S. pneumoniae is a major human pathogen that is carried asymptomatically in the nasopharynx by up to 70% of the population; however, transition to internal sites can cause a range of diseases such as pneumonia, otitis media, meningitis and bacteraemia. S. pyogenes is a human pathogen responsible for diseases ranging from pharyngitis and impetigo, to severe invasive infections. Both species have overlapping capacity with respect to metal acquisition, export and regulation and how metal homeostasis relates to their virulence and ability to invade and survive within the host. It is becoming more apparent that metals have an important role to play in the control of infection, and with further investigations, it could lead to the potential use of metals in novel antimicrobial therapies.

Characteristics of a water-forming NADH oxidase from Methanobrevibacter smithii, an archaeon in the human gut

NOX-ms catalysed the oxidization of NADH and converted O₂ to H₂O by using cysteine-mediated electron transfer. Its transcription was increased by oxidative stress and glucose.

NADH oxidases (NOXs) catalysing the oxidation of NADH to yield NAD⁺ and H₂O, H₂O₂, or both play an important role in protecting organisms from oxidative stress and maintaining the balance of NAD⁺/NADH. A gene encoding NOX was identified from Methanobrevibacter smithii (NOX-ms), the predominant archaeon in the human gut ecosystem. Subsequent analyses showed that it is an FAD-containing protein with a subunit molecular mass of 48 kDa. NOX-ms was purified to homogeneity after expression in Escherichia coli. NOX-ms catalysed the oxidization of NADH and converted O₂ to H₂O with an optimal pH of 7.5 and a temperature optimum of approximately 37°C. The V_max and K_m values were 42.6–44.1 unit/mg and 47.8–54.6 μM for NADH. The apparent V_max and K_m for oxygen were 189.5–196.1 unit/mg and 14.6–16.8 μM. The mutation analysis suggests that Cys⁴² in NOX-ms plays a key role in the four-electron reduction of O₂ to H₂O. Quantitative reverse transcription-PCR (RT-qPCR) revealed that transcription of NOX-ms was also up-regulated after exposing the cells to oxidative stress and glucose. Finally, the potential of NOX-ms as a target to control colonization of M. smithii and its possible applications are discussed.

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.

Structural Analysis of Streptococcus pyogenes NADH Oxidase: Conformational Dynamics Involved in Formation of the C(4a)-Peroxyflavin Intermediate

In probing the oxygen reactivity of an Enterococcus faecalis NADH oxidase (Nox; O2 → 2H2O) C42S mutant lacking the Cys42-sulfenic acid (Cys42-SOH) redox center, we provided direct evidence of a C(4a)-peroxyflavin intermediate in the oxidative half-reaction and also described a conformational or chemical change that is rate-limiting for full reoxidation of the homodimer. In this work, the Nox from Streptococcus pyogenes (SpyNox) has been expressed and crystallized, and the overoxidized wild-type [Cys44-SOH → Cys44-sulfinic acid (Cys44-SO2H)] and C44S mutant enzyme structures have been refined at 2.0 and 2.15 Å, respectively. We show that azide binds to the two-electron reduced wild-type (EH2) enzyme and to the mutant enzyme in solution, but with a significantly higher affinity for the mutant protein. The spectral course of the titration with the SpyNox EH2 form clearly indicates progressive displacement of the Cys44-S(-) → FAD charge-transfer interaction. An azide soak with C44S Nox crystals led to the structure of the complex, as refined at 2.10 Å. The active-site N3(-) ligand is proximal to the Ser44 and His11 side chains, and a significant shift in the Ser44 side chain also appears. This provides an attractive explanation for the azide-induced loss of charge-transfer absorbance seen with the wild-type EH2 form and also permits accommodation of a C(4a)-peroxyflavin structural model. The conformation of Ser44 and the associated helical element, and the resulting steric accommodation, appear to be linked to the conformational change described in the E. faecalis C42S Nox oxidative half-reaction.

Complete genome sequence of Lactobacillus salivarius Ren, a probiotic strain with anti-tumor activity

Lactobacillus salivarius Ren (LsR) (CGMCC No. 3606) is a probiotic strain that was isolated from the feces of a healthy centenarian living in Bama, Guangxi, China. Previous studies have shown that this strain decreases 4-nitroquinoline 1-oxide (4-NQO)-induced genotoxicity in vitro. It also suppresses 4-NQO-induced oral carcinogenesis and 1,2-dimethylhydrazine (DMH)-induced colorectal carcinogenesis, and therefore may be used as an adjuvant therapeutic agent for cancer. Here, we report the complete genome sequence of LsR that consists of a circular chromosome of 1751,565 bp and two plasmids (pR1, 176,951 bp; pR2, 49,848 bp).

Phylogenomic analysis and predicted physiological role of the proton-translocating NADH:quinone oxidoreductase (complex I) across bacteria

The proton-translocating NADH:quinone oxidoreductase (complex I) is a multisubunit integral membrane enzyme found in the respiratory chains of both bacteria and eukaryotic organelles. Although much research has focused on the enzyme's central role in the mitochondrial respiratory chain, comparatively little is known about its role in the diverse energetic lifestyles of different bacteria. Here, we used a phylogenomic approach to better understand the distribution of complex I across bacteria, the evolution of this enzyme, and its potential roles in shaping the physiology of different bacterial groups. By surveying 970 representative bacterial genomes, we predict complex I to be present in ~50% of bacteria. While this includes bacteria with a wide range of energetic schemes, the presence of complex I is associated with specific lifestyles, including aerobic respiration and specific types of phototrophy (bacteria with only a type II reaction center). A phylogeny of bacterial complex I revealed five main clades of enzymes whose evolution is largely congruent with the evolution of the bacterial groups that encode complex I. A notable exception includes the gammaproteobacteria, whose members encode one of two distantly related complex I enzymes predicted to participate in different types of respiratory chains (aerobic versus anaerobic). Comparative genomic analyses suggest a broad role for complex I in reoxidizing NADH produced from various catabolic reactions, including the tricarboxylic acid (TCA) cycle and fatty acid beta-oxidation. Together, these findings suggest diverse roles for complex I across bacteria and highlight the importance of this enzyme in shaping diverse physiologies across the bacterial domain.

IMPORTANCE

Living systems use conserved energy currencies, including a proton motive force (PMF), NADH, and ATP. The respiratory chain enzyme, complex I, connects these energy currencies by using NADH produced during nutrient breakdown to generate a PMF, which is subsequently used for ATP synthesis. Our goal is to better understand the role of complex I in bacteria, whose energetic diversity allows us to view its function in a range of biological contexts. We analyzed sequenced bacterial genomes to predict the presence, evolution, and function of complex I in bacteria. We identified five main classes of bacterial complex I and predict that different classes participate in different types of respiratory chains (aerobic and anaerobic). We also predict that complex I helps maintain a cellular redox state by reoxidizing NADH produced from central metabolism. Our findings suggest diverse roles for complex I in bacterial physiology, highlighting the need for future laboratory-based studies.

Mechanisms of group A Streptococcus resistance to reactive oxygen species

Streptococcus pyogenes, also known as group A Streptococcus (GAS), is an exclusively human Gram-positive bacterial pathogen ranked among the ‘top 10’ causes of infection-related deaths worldwide. GAS commonly causes benign and self-limiting epithelial infections (pharyngitis and impetigo), and less frequent severe invasive diseases (bacteremia, toxic shock syndrome and necrotizing fasciitis). Annually, GAS causes 700 million infections, including 1.8 million invasive infections with a mortality rate of 25%. In order to establish an infection, GAS must counteract the oxidative stress conditions generated by the release of reactive oxygen species (ROS) at the infection site by host immune cells such as neutrophils and monocytes. ROS are the highly reactive and toxic byproducts of oxygen metabolism, including hydrogen peroxide (H₂O₂), superoxide anion (O₂•⁻), hydroxyl radicals (OH•) and singlet oxygen (O₂*), which can damage bacterial nucleic acids, proteins and cell membranes. This review summarizes the enzymatic and regulatory mechanisms utilized by GAS to thwart ROS and survive under conditions of oxidative stress.

This review discusses the mechanisms utilized by the bacterial pathogen group A Streptococcus to detoxify reactive oxygen species and survive in the human host under conditions of oxidative stress.

Oxygen-dependent phenotypic variation in group A streptococcus

BACKGROUND

The phenotypic heterogeneity of the human pathogen Streptococcus pyogenes [group A streptococcus (GAS)] is associated with bacterial virulence variation. During invasive GAS infection, mutations in the two-component regulatory system covR/covS leads to increases in hyaluronic acid capsule production, virulence genes expression, and lethality in the mouse infection model. Phenotypic variation of GAS is also found under in vitro culture conditions. However, whether a specific environmental factor is important for phenotypic variation is still unknown.

METHODS

GAS968 is an emm12-type clinical isolate that converts from mucoid to hypermucoid morphology under in vitro culture conditions. To clarify whether morphology variation can be triggered by specific environmental signals, or whether different morphology variants would be selected under specific environmental stresses, GAS968 was cultured under different conditions, and the changes in the number of mucoid and hypermucoid colonies in the total bacterial population were analyzed.

RESULTS

The ratio of mucoid and hypermucoid colonies of GAS968 in the total bacterial population changes dramatically under aerobic and anaerobic conditions. The decrease in the number of hypermucoid colonies in the total bacterial population under aerobic conditions is not caused by growth repression, suggesting that the morphology conversion of GAS968 is inhibited by oxygen.

CONCLUSION

Phenotypic heterogeneity has been shown to contribute to invasive GAS infection. Our results suggest that oxygen-dependent morphology variation in GAS968 may have important roles in bacterial pathogenesis.

Ethanol-induced alcohol dehydrogenase E (AdhE) potentiates pneumolysin in Streptococcus pneumoniae

Alcohol impairs the host immune system, rendering the host more vulnerable to infection. Therefore, alcoholics are at increased risk of acquiring serious bacterial infections caused by Streptococcus pneumoniae, including pneumonia. Nevertheless, how alcohol affects pneumococcal virulence remains unclear. Here, we showed that the S. pneumoniae type 2 D39 strain is ethanol tolerant and that alcohol upregulates alcohol dehydrogenase E (AdhE) and potentiates pneumolysin (Ply). Hemolytic activity, colonization, and virulence of S. pneumoniae, as well as host cell myeloperoxidase activity, proinflammatory cytokine secretion, and inflammation, were significantly attenuated in adhE mutant bacteria (ΔadhE strain) compared to D39 wild-type bacteria. Therefore, AdhE might act as a pneumococcal virulence factor. Moreover, in the presence of ethanol, S. pneumoniae AdhE produced acetaldehyde and NADH, which subsequently led Rex (redox-sensing transcriptional repressor) to dissociate from the adhE promoter. An increase in AdhE level under the ethanol condition conferred an increase in Ply and H2O2 levels. Consistently, S. pneumoniae D39 caused higher cytotoxicity to RAW 264.7 cells than the ΔadhE strain under the ethanol stress condition, and ethanol-fed mice (alcoholic mice) were more susceptible to infection with the D39 wild-type bacteria than with the ΔadhE strain. Taken together, these data indicate that AdhE increases Ply under the ethanol stress condition, thus potentiating pneumococcal virulence.

Role of surface residue 184 in the catalytic activity of NADH oxidase from Streptococcus pyogenes

Nicotinamide adenine dinucleotide (NADH) oxidase from Streptococcus pyogenes (SpNox) is a flavoprotein harboring one molecule of noncovalently bound flavin adenine dinucleotide. It catalyzes the oxidation of NADH by reducing molecular O2 to H2O directly through a four-electron reduction. In this study, we selected the lysine residues on the surface of SpNox and mutated them into arginine residues to study the effect on the enzyme activity. A single-point mutation (K184R) at the surface of SpNox enhanced NADH oxidase activity by approximately 50 % and improved thermostability with 46.6 % longer half life at 30 °C. Further insights into the function of residue K184 were obtained by substituting it with other nonpolar, polar, positively charged, and negatively charged residues. To elucidate the role of this residue, computer-assisted molecular modeling and substrate docking were performed. The results demonstrate that even a single mutation at the surface of the enzyme induces changes in the interaction at the active site and affects the activity and stability. Additionally, the data also suggest that the K184R mutant can be used as an effective biocatalyst for NAD(+) regeneration in L-rare sugar production.

Distinct structural features of the peroxide response regulator from group A Streptococcus drive DNA binding

Group A streptococcus (GAS, Streptococcus pyogenes) is a strict human pathogen that causes severe, invasive diseases. GAS does not produce catalase, but has an ability to resist killing by reactive oxygen species (ROS) through novel mechanisms. The peroxide response regulator (PerR), a member of ferric uptake regulator (Fur) family, plays a key role for GAS to cope with oxidative stress by regulating the expression of multiple genes. Our previous studies have found that expression of an iron-binding protein, Dpr, is under the direct control of PerR. To elucidate the molecular interactions of PerR with its cognate promoter, we have carried out structural studies on PerR and PerR-DNA complex. By combining crystallography and small-angle X-ray scattering (SAXS), we confirmed that the determined PerR crystal structure reflects its conformation in solution. Through mutagenesis and biochemical analysis, we have identified DNA-binding residues suggesting that PerR binds to the dpr promoter at the per box through a winged-helix motif. Furthermore, we have performed SAXS analysis and resolved the molecular architecture of PerR-DNA complex, in which two 30 bp DNA fragments wrap around two PerR homodimers by interacting with the adjacent positively-charged winged-helix motifs. Overall, we provide structural insights into molecular recognition of DNA by PerR and define the hollow structural arrangement of PerR-30bpDNA complex, which displays a unique topology distinct from currently proposed DNA-binding models for Fur family regulators.

The impairment of methylmenaquinol:fumarate reductase affects hydrogen peroxide susceptibility and accumulation in Campylobacter jejuni

The methylmenaquinol:fumarate reductase (Mfr) of Campylobacter jejuni is a periplasmic respiratory (redox) protein that contributes to the metabolism of fumarate and displays homology to succinate dehydrogenase (Sdh). Since chemically oxidized redox-enzymes, including fumarate reductase and Sdh, contribute to the generation of oxidative stress in Escherichia coli, we assessed the role of Mfr in C. jejuni after exposure to hydrogen peroxide (H2 O2 ). Our results show that a Mfr mutant (∆mfrA) strain was less susceptible to H2 O2 as compared to the wildtype (WT). Furthermore, the H2 O2 concentration in the ∆mfrA cultures was significantly higher than that of WT after exposure to the oxidant. In the presence of H2 O2 , catalase (KatA) activity and katA expression were significantly lower in the ∆mfrA strain as compared to the WT. Exposure to H2 O2 resulted in a significant decrease in total intracellular iron in the ∆mfrA strain as compared to WT, while the addition of iron to the growth medium mitigated H2 O2 susceptibility and accumulation in the mutant. The ∆mfrA strain was significantly more persistent in RAW macrophages as compared to the WT. Scanning electron microscopy showed that infection with the ∆mfrA strain caused prolonged changes to the macrophages' morphology, mainly resulting in spherical-shaped cells replete with budding structures and craters. Collectively, our results suggest a role for Mfr in maintaining iron homeostasis in H2 O2 stressed C. jejuni, probably via affecting the concentrations of intracellular iron.

NADH Oxidase of Streptococcus thermophilus 1131 is Required for the Effective Yogurt Fermentation with Lactobacillus delbrueckii subsp. bulgaricus 2038

We previously reported that dissolved oxygen (DO) suppresses yogurt fermentation with an industrial starter culture composed of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) 2038 and Streptococcus thermophilus 1131, and also found that reducing the DO in the medium prior to fermentation (deoxygenated fermentation) shortens the fermentation time. In this study, we found that deoxygenated fermentation primarily increased the cell number of S. thermophilus 1131 rather than that of L. bulgaricus 2038, resulting in earlier l-lactate and formate accumulation. Measurement of the DO concentration and hydrogen peroxide generation in the milk medium suggested that DO is mainly removed by S. thermophilus 1131. The results using an H2O-forming NADH oxidase (Nox)-defective mutant of S. thermophilus 1131 revealed that Nox is the major oxygen-consuming enzyme of the bacterium. Yogurt fermentation with the S. thermophilus Δnox mutant and L. bulgaricus 2038 was significantly slower than with S. thermophilus 1131 and L. bulgaricus 2038, and the DO concentrations of the mixed culture did not decrease to less than 2 mg/kg within 3 hr. These observations suggest that Nox of S. thermophilus 1131 contributes greatly to yogurt fermentation, presumably by removing the DO in milk.

Emergence of hypervirulent mutants resistant to early clearance during systemic serotype 1 pneumococcal infection in mice and humans

BACKGROUND

Streptococcus pneumoniae serotype 1 has a high likelihood of causing invasive disease. Serotype 1 isolates belonging to CC228 are associated with low mortality, while CC217 isolates exhibit high mortality in patients.

METHODS

Clinical pneumococcal isolates and mutants were evaluated in wild-type C57BL/6 mice, macrophage-depleted mice, neutrophil-depleted mice, and SIGN-R1 knockout mice. In vitro models included binding and phagocytosis by THP-1 cells, capsule measurements, hydrogen peroxide production, and viability assays.

RESULTS

During early systemic infection in mice with serotype 1, large-colony variants appeared in blood. Similar large colonies were found in blood specimens from patients with invasive disease. Large morphotypes contained higher numbers of viable bacteria, grew faster, produced no or little hydrogen peroxide, and contained mutations in the spxB gene. spxB mutants were considerably more virulent in wild-type mice, less susceptible to early host clearance than wild-type strains after intravenous infection, but impaired in colonization. spxB mutants were less efficiently phagocytosed by macrophages than wild-type bacteria, which, in contrast to spxB mutants, caused more-severe disease when macrophages or SIGN-R1 were depleted.

CONCLUSIONS

Hypervirulent spxB mutants are selected in both mice and patients and are resistant to early macrophage-mediated clearance.

Crystal structure of peroxide stress regulator from Streptococcus pyogenes provides functional insights into the mechanism of oxidative stress sensing

Regulation of oxidative stress responses by the peroxide stress regulator (PerR) is critical for the in vivo fitness and virulence of group A Streptococcus. To elucidate the molecular mechanism of DNA binding, peroxide sensing, and gene regulation by PerR, we performed biochemical and structural characterization of PerR. Sequence-specific DNA binding by PerR does not require regulatory metal occupancy. However, metal binding promotes higher affinity PerR-DNA interactions. PerR metallated with iron directly senses peroxide stress and dissociates from operator sequences. The crystal structure revealed that PerR exists as a homodimer with two metal-binding sites per subunit as follows: a structural zinc site and a regulatory metal site that is occupied in the crystals by nickel. The regulatory metal-binding site in PerR involves a previously unobserved HXH motif located in its unique N-terminal extension. Mutational analysis of the regulatory site showed that the PerR metal ligands are involved in regulatory metal binding, and integrity of this site is critical for group A Streptococcus virulence. Interestingly, the metal-binding HXH motif is not present in the structurally characterized members of ferric uptake regulator (Fur) family but is fully conserved among PerR from the genus Streptococcus. Thus, it is likely that the PerR orthologs from streptococci share a common mechanism of metal binding, peroxide sensing, and gene regulation that is different from that of well characterized PerR from Bacillus subtilis. Together, our findings provide key insights into the peroxide sensing and regulation of the oxidative stress-adaptive responses by the streptococcal subfamily of PerR.

Murine vaginal colonization model for investigating asymptomatic mucosal carriage of Streptococcus pyogenes

While many virulence factors promoting Streptococcus pyogenes invasive disease have been described, specific streptococcal factors and host properties influencing asymptomatic mucosal carriage remain uncertain. To address the need for a refined model of prolonged S. pyogenes asymptomatic mucosal colonization, we have adapted a preestrogenized murine vaginal colonization model for S. pyogenes. In this model, derivatives of strains HSC5, SF370, JRS4, NZ131, and MEW123 established a reproducible, asymptomatic colonization of the vaginal mucosa over a period of typically 3 to 4 weeks' duration at a relatively high colonization efficiency. Prior treatment with estradiol prolonged streptococcal colonization and was associated with reduced inflammation in the colonized vaginal epithelium as well as a decreased leukocyte presence in vaginal fluid compared to the levels of inflammation and leukocyte presence in non-estradiol-treated control mice. The utility of our model for investigating S. pyogenes factors contributing to mucosal carriage was verified, as a mutant with a mutation in the transcriptional regulator catabolite control protein A (CcpA) demonstrated significant impairment in vaginal colonization. An assessment of in vivo transcriptional activity in the CcpA(-) strain for several known CcpA-regulated genes identified significantly elevated transcription of lactate oxidase (lctO) correlating with excessive generation of hydrogen peroxide to self-lethal levels. Deletion of lctO did not impair colonization, but deletion of lctO in a CcpA(-) strain prolonged carriage, exceeding even that of the wild-type strain. Thus, while LctO is not essential for vaginal colonization, its dysregulation is deleterious, highlighting the critical role of CcpA in promoting mucosal colonization. The vaginal colonization model should prove effective for future analyses of S. pyogenes mucosal colonization.

Heme proteins in lactic acid bacteria

Lactic acid bacteria (LAB) are of profound importance in food production and infection medicine. LAB do not rely on heme (protoheme IX) for growth and are unable to synthesize this cofactor but are generally able to assemble a small repertoire of heme-containing proteins if heme is provided from an exogenous source. These features are in contrast to other bacteria, which synthesize their heme or depend on heme for growth. We here present the cellular function of heme proteins so far identified in LAB and discuss their biogenesis as well as applications of the extraordinary heme physiology of LAB.

Biochemistry and evolution of anaerobic energy metabolism in eukaryotes

Major insights into the phylogenetic distribution, biochemistry, and evolutionary significance of organelles involved in ATP synthesis (energy metabolism) in eukaryotes that thrive in anaerobic environments for all or part of their life cycles have accrued in recent years. All known eukaryotic groups possess an organelle of mitochondrial origin, mapping the origin of mitochondria to the eukaryotic common ancestor, and genome sequence data are rapidly accumulating for eukaryotes that possess anaerobic mitochondria, hydrogenosomes, or mitosomes. Here we review the available biochemical data on the enzymes and pathways that eukaryotes use in anaerobic energy metabolism and summarize the metabolic end products that they generate in their anaerobic habitats, focusing on the biochemical roles that their mitochondria play in anaerobic ATP synthesis. We present metabolic maps of compartmentalized energy metabolism for 16 well-studied species. There are currently no enzymes of core anaerobic energy metabolism that are specific to any of the six eukaryotic supergroup lineages; genes present in one supergroup are also found in at least one other supergroup. The gene distribution across lineages thus reflects the presence of anaerobic energy metabolism in the eukaryote common ancestor and differential loss during the specialization of some lineages to oxic niches, just as oxphos capabilities have been differentially lost in specialization to anoxic niches and the parasitic life-style. Some facultative anaerobes have retained both aerobic and anaerobic pathways. Diversified eukaryotic lineages have retained the same enzymes of anaerobic ATP synthesis, in line with geochemical data indicating low environmental oxygen levels while eukaryotes arose and diversified.

From meadows to milk to mucosa - adaptation of Streptococcus and Lactococcus species to their nutritional environments

Lactic acid bacteria (LAB) are indigenous to food-related habitats as well as associated with the mucosal surfaces of animals. The LAB family Streptococcaceae consists of the genera Lactococcus and Streptococcus. Members of the family include the industrially important species Lactococcus lactis, which has a long history safe use in the fermentative food industry, and the disease-causing streptococci Streptococcus pneumoniae and Streptococcus pyogenes. The central metabolic pathways of the Streptococcaceae family have been extensively studied because of their relevance in the industrial use of some species, as well as their influence on virulence of others. Recent developments in high-throughput proteomic and DNA-microarray techniques, in in vivo NMR studies, and importantly in whole-genome sequencing have resulted in new insights into the metabolism of the Streptococcaceae family. The development of cost-effective high-throughput sequencing has resulted in the publication of numerous whole-genome sequences of lactococcal and streptococcal species. Comparative genomic analysis of these closely related but environmentally diverse species provides insight into the evolution of this family of LAB and shows that the relatively small genomes of members of the Streptococcaceae family have been largely shaped by the nutritionally rich environments they inhabit.

Characterization of H2O-forming NADH oxidase from Streptococcus pyogenes and its application in l-rare sugar production

A nicotinamide adenine dinucleotide (NADH) oxidase from Streptococcus pyogenes MGAS10394 (SpNox) was cloned and overexpressed in Escherichia coli BL21 (DE3). The purified SpNox enzyme had optimal pH and temperature of 7.0 and 55°C, respectively, with a K(m) of 27.0μM and a k(cat)/K(m) of 1.1×10(7)s(-1)M(-1). SpNox showed the highest activity among all known NADH oxidases, and site-directed mutagenesis and docking analysis shed light on the molecular basis of its unusually high activity. The characteristics of SpNox may prove to be useful for NAD(+) regeneration in the production of l-rare sugar.

The coenzyme A disulphide reductase of Borrelia burgdorferi is important for rapid growth throughout the enzootic cycle and essential for infection of the mammalian host

In a microarray analysis of the RpoS regulon in mammalian host-adapted Borrelia burgdorferi, bb0728 (cdr) was found to be dually transcribed by the sigma factors σ(70) and RpoS. The cdr gene encodes a coenzyme A disulphide reductase (CoADR) that reduces CoA-disulphides to CoA in an NADH-dependent manner. Based on the abundance of CoA in B. burgdorferi and the biochemistry of the enzyme, CoADR has been proposed to play a role in the spirochaete's response to reactive oxygen species. To better understand the physiologic function(s) of BbCoADR, we generated a B. burgdorferi mutant in which the cdr gene was disrupted. RT-PCR and 5'-RACE analysis revealed that cdr and bb0729 are co-transcribed from a single transcriptional start site upstream of the bb0729 coding sequence; a shuttle vector containing the bb0729-cdr operon and upstream promoter element was used to complement the cdr mutant. Although the mutant was no more sensitive to hydrogen peroxide than its parent, it did exhibit increased sensitivity to high concentrations of t-butyl-hydroperoxide, an oxidizing compound that damages spirochetal membranes. Characterization of the mutant during standard (15% oxygen, 6% CO(2)) and anaerobic (< 1% O(2) , 9-13% CO(2)) cultivation at 37°C revealed a growth defect under both conditions that was particularly striking during anaerobiosis. The mutant was avirulent by needle inoculation and showed decreased survival in feeding nymphs, but displayed no survival defect in unfed flat nymphs. Based on these results, we propose that BbCoADR is necessary to maintain optimal redox ratios for CoA/CoA-disulphide and NAD(+) /NADH during periods of rapid replication throughout the enzootic cycle, to support thiol-disulphide homeostasis, and to indirectly protect the spirochaete against peroxide-mediated membrane damage; one or more of these functions are essential for infection of the mammalian host by B. burgdorferi.

Analysis of group A Streptococcus gene expression in humans with pharyngitis using a microarray

Pharyngitis caused by group A streptococci (GAS) is one of the most common infections around the world. However, relatively little is known about which genes are expressed and which genes regulate expression during acute infection. Due to their ability to provide genome-wide views of gene expression at one time, microarrays are increasingly being incorporated in GAS research. In this study, a novel electrochemical detection-based microarray was used to identify gene expression patterns among humans with culture-confirmed GAS pharyngitis. Using 14 samples (11 GAS-positive and three GAS-negative) obtained from subjects seen at the Brooke Army Medical Center paediatric clinic, this study demonstrated two different clusters of gene expression patterns. One cluster expressed a larger number of genes related to phages, immune-system evasion and survival among competing oral flora, signifying a potentially more virulent pattern of gene expression. The other cluster showed a greater number of genes related to nutrient acquisition and protein expression. This in vivo genome-wide analysis of GAS gene expression in humans with pharyngitis evaluated global gene expression in terms of virulence factors.

Differential secretomics of Streptococcus pyogenes reveals a novel peroxide regulator (PerR)-regulated extracellular virulence factor mitogen factor 3 (MF3)

Streptococcus pyogenes is a human pathogen that causes various diseases. Numerous virulence factors secreted by S. pyogenes are involved in pathogenesis. The peroxide regulator (PerR) is associated with the peroxide resistance response and pathogenesis, but little is known about the regulation of the secretome involved in virulence. To investigate how PerR regulates the expression of the S. pyogenes secretome involved in virulence, a perR deficient mutant was used for comparative secretomic analysis with a wild-type strain. The conditioned medium containing secreted proteins of a wild-type strain and a perR deficient mutant at the stationary phase were collected for two-dimensional gel electrophoresis analysis, where protease inhibitors were applied to avoid the degradation of extracellular proteins. Differentially expressed protein spots were identified by liquid chromatography electrospray ionization tandem MS. More than 330 protein spots were detected on each gel. We identified 25 unique up-regulated proteins and 13 unique down-regulated proteins that were directly or indirectly controlled by the PerR regulator. Among these identified proteins, mitogen factor 3 (MF3), was selected to verify virulence and the expression of gene products. The data showed that MF3 protein levels in conditioned medium, as measured by immunoblot analysis, correlated well with protein levels determined by two-dimensional gel electrophoresis analysis. We also demonstrated that PerR bound to the promoter region of the mf3 gene. The result of an infection model showed that virulence was attenuated in the mf3 deficient mutant. Additional growth data of the wild-type strain and the mf3 deficient mutant suggested that MF3 played a role in digestion of exogenous DNA for promoting growth. To summarize, we conclude that PerR can positively regulate the expression of the secreted protein MF3 that contributes to the virulence in S. pyogenes. The analysis of the PerR-regulated secretome provided key information for the elucidation of the host-pathogen interactions and might assist in the development of potential chemotherapeutic strategies to prevent or treat streptococcal diseases.

Identification of a conserved sequence in flavoproteins essential for the correct conformation and activity of the NADH oxidase NoxE of Lactococcus lactis

Water-forming NADH oxidases (encoded by noxE, nox2, or nox) are flavoproteins generally implicated in the aerobic survival of microaerophilic bacteria, such as lactic acid bacteria. However, some natural Lactococcus lactis strains produce an inactive NoxE. We examined the role of NoxE in the oxygen tolerance of L. lactis in the rich synthetic medium GM17. Inactivation of noxE suppressed 95% of NADH oxidase activity but only slightly affected aerobic growth, oxidative stress resistance, and NAD regeneration. However, noxE inactivation strongly impaired oxygen consumption and mixed-acid fermentation. We found that the A303T mutation is responsible for the loss of activity of a naturally occurring variant of NoxE. Replacement of A303 with T or G or of G307 with S or A by site-directed mutagenesis led to NoxE aggregation and the total loss of activity. We demonstrated that L299 is involved in NoxE activity, probably contributing to positioning flavin adenine dinucleotide (FAD) in the active site. These residues are part of the strongly conserved sequence LA(T)XXAXXXG included in an alpha helix that is present in other flavoprotein disulfide reductase (FDR) family flavoproteins that display very similar three-dimensional structures.

The Streptococcus pyogenes proteome: maps, virulence factors and vaccine candidates

Streptococcus pyogenes is an important cause of human morbidity and mortality worldwide. A wealth of genomic information related to this pathogen has facilitated exploration of the proteome, particularly in response to environmental conditions thought to mimic various aspects of pathogenesis. Proteomic approaches are also used to identify immunoreactive proteins for vaccine development and to identify proteins that may induce autoimmunity. These studies have revealed new mechanisms involved in regulating the S. pyogenes proteome, which has opened up new avenues in the study of S. pyogenes pathogenesis. This article describes the methods used, and progress being made towards characterizing the S. pyogenes proteome, including studies seeking to identify potential vaccine candidates.

Comparative analysis of plasmids in the genus Listeria

BACKGROUND

We sequenced four plasmids of the genus Listeria, including two novel plasmids from L. monocytogenes serotype 1/2c and 7 strains as well as one from the species L. grayi. A comparative analysis in conjunction with 10 published Listeria plasmids revealed a common evolutionary background.

PRINCIPAL FINDINGS

All analysed plasmids share a common replicon-type related to theta-replicating plasmid pAMbeta1. Nonetheless plasmids could be broadly divided into two distinct groups based on replicon diversity and the genetic content of the respective plasmid groups. Listeria plasmids are characterized by the presence of a large number of diverse mobile genetic elements and a commonly occurring translesion DNA polymerase both of which have probably contributed to the evolution of these plasmids. We detected small non-coding RNAs on some plasmids that were homologous to those present on the chromosome of L. monocytogenes EGD-e. Multiple genes involved in heavy metal resistance (cadmium, copper, arsenite) as well as multidrug efflux (MDR, SMR, MATE) were detected on all listerial plasmids. These factors promote bacterial growth and survival in the environment and may have been acquired as a result of selective pressure due to the use of disinfectants in food processing environments. MDR efflux pumps have also recently been shown to promote transport of cyclic diadenosine monophosphate (c-di-AMP) as a secreted molecule able to trigger a cytosolic host immune response following infection.

CONCLUSIONS

The comparative analysis of 14 plasmids of genus Listeria implied the existence of a common ancestor. Ubiquitously-occurring MDR genes on plasmids and their role in listerial infection now deserve further attention.

CcpA and LacD.1 affect temporal regulation of Streptococcus pyogenes virulence genes

Production of H(2)O(2) follows a growth phase-dependent pattern that mimics that of many virulence factors of Streptococcus pyogenes. To gain greater insight into mechanisms coupling virulence factor expression to growth phase, we investigated the molecular basis for H(2)O(2) generation and its regulation. Deletion of the gene encoding lactate oxidase (lctO) or culture in the presence of glucose eliminated H(2)O(2) production, implicating carbohydrate regulation of lctO as a key element of growth phase control. In examining known carbohydrate-responsive regulators, deletion of the gene encoding CcpA but not that encoding LacD.1 resulted in both derepression and an uncoupling of lctO transcription from its growth phase pattern. Expanding this analysis to additional virulence factors demonstrated both negative (cfa, encoding CAMP factor) and positive (speB, encoding a cysteine protease) regulation by CcpA and that CcpA mutants were highly cytotoxic for cultured macrophages. This latter property resulted from enhanced transcription of the streptolysin S biogenesis operon. Examination of CcpA-promoter interactions using a DNA pull-down assay mimicking physiological conditions showed direct binding to the promoters of lctO and speB but not those of sagA. CcpA but not LacD.1 mutants were attenuated in a murine model of soft-tissue infection, and analysis of gene expression in infected tissue indicated that CcpA mutants had altered expression of lctO, cfa, and speB but not the indirectly regulated sagA gene. Taken together, these data show that CcpA regulates virulence genes via at least three distinct mechanisms and that disruption of growth phase regulation alters transcriptional patterns in infected tissues.

Characterization of clinical Enterococcus faecalis small-colony variants

In this report, we present a clinical case of chronic aortic valve endocarditis caused by Enterococcus faecalis small-colony variants (SCVs), with ensuing characterization of the SCV phenotype in comparison to the clonally related normal phenotype with respect to alterations in microscopic and ultrastructural morphology, growth behavior, and metabolic pathways. In contrast to the normal phenotype, light and electron microscopy of the Enterococcus SCVs demonstrated the presence of heterogeneous cells of different sizes with aberrant shapes. Furthermore, SCVs showed excessive production of an intercellular substance and alterations in cell division displayed by a thick, coarse cell wall and incomplete, branched, and multiple cross walls without obvious cell separation. In addition, empty "ghost" cells were visible. In growth experiments, SCVs displayed an extended lag phase with delayed entrance into the stationary phase. Interestingly, SCV cells growing under aerobic conditions did not attain the growth and viability of the normal phenotype or those of SCVs growing under microaerobic conditions, suggesting impaired growth behavior and enhanced vulnerability in the presence of oxygen. By metabolite analysis, SCVs failed to produce significant amounts of acetate or lactate under aerobic growth conditions but were able to produce lactate under microaerobic growth conditions, implicating the induction of a fermentative metabolism. In conclusion, the observed structural alterations and changes in the cellular growth and metabolic pathways facilitated the survival of Enterococcus SCVs under microaerobic conditions in vitro and thus presumably in vivo during endocarditis.

Microbial production of low molecular weight hyaluronic acid by adding hydrogen peroxide and ascorbate in batch culture of Streptococcus zooepidemicus

Microbial production of low molecular weight hyaluronic acid (HA) by the addition of hydrogen peroxide and ascorbate during the batch culture of Streptococcus zooepidemicus was investigated. Hydrogen peroxide (1.0 mmol/g HA) and ascorbate (0.5 mmol/g HA) were added at 8h and 12h to degrade HA. With the redox depolymerization of HA, the HA molecular weight decreased from 1,300 kDa for the control to 80 kDa, and the average broth viscosity during 8-16 h decreased from 360 mPa s for the control to 290 mPa s. The average oxygen mass transfer coefficient K(L)a increased from 10h(-1) for the control to 35 h(-1) and the average dissolved oxygen level increased from 1% of air saturation in the control to 10%. HA production increased from 5.0 g/L for the control to 6.5 g/L, and contributed to the increased redox potential and energy charge. This novel process not only significantly enhanced production of low molecular weight HA, but also improved purification efficiency due to a decreased broth viscosity. Low molecular weight HA finds applications in biomedical and healthcare fields.

Hexameric ring structure of a thermophilic archaeon NADH oxidase that produces predominantly H2O

An NADH oxidase (NOX) was cloned from the genome of Thermococcus profundus (NOXtp) by genome walking, and the encoded protein was purified to homogeneity after expression in Escherichia coli. Subsequent analyses showed that it is an FAD-containing protein with a subunit molecular mass of 49 kDa that exists as a hexamer with a native molecular mass of 300 kDa. A ring-shaped hexameric form was revealed by electron microscopic and image processing analyses. NOXtp catalyzed the oxidization of NADH and NADPH and predominantly converted O(2) to H(2)O, but not to H(2)O(2), as in the case of most other NOX enzymes. To our knowledge, this is the first example of a NOX that can produce H(2)O predominantly in a thermophilic organism. As an enzyme with two cysteine residues, NOXtp contains a cysteinyl redox center at Cys45 in addition to FAD. Mutant analysis suggests that Cys45 in NOXtp plays a key role in the four-electron reduction of O(2) to H(2)O, but not in the two-electron reduction of O(2) to H(2)O(2).