Cloning of the sodA gene from Corynebacterium melassecola and role of superoxide dismutase in cellular viability

Corynebacterium diphtheriae Proteome Adaptation to Cell Culture Medium and Serum

Host-pathogen interactions are often studied in vitro using primary or immortal cell lines. This set-up avoids ethical problems of animal testing and has the additional advantage of lower costs. However, the influence of cell culture media on bacterial growth and metabolism is not considered or investigated in most cases. To address this question growth and proteome adaptation of Corynebacterium diphtheriae strain ISS3319 were investigated in this study. Bacteria were cultured in standard growth medium, cell culture medium, and fetal calf serum. Mass spectrometric analyses and label-free protein quantification hint at an increased bacterial pathogenicity when grown in cell culture medium as well as an influence of the growth medium on the cell envelope.

Co-Expression Networks for Causal Gene Identification Based on RNA-Seq Data of Corynebacterium pseudotuberculosis

Corynebacterium pseudotuberculosis is a Gram-positive bacterium that causes caseous lymphadenitis, a disease that predominantly affects sheep, goat, cattle, buffalo, and horses, but has also been recognized in other animals. This bacterium generates a severe economic impact on countries producing meat. Gene expression studies using RNA-Seq are one of the most commonly used techniques to perform transcriptional experiments. Computational analysis of such data through reverse-engineering algorithms leads to a better understanding of the genome-wide complexity of gene interactomes, enabling the identification of genes having the most significant functions inferred by the activated stress response pathways. In this study, we identified the influential or causal genes from four RNA-Seq datasets from different stress conditions (high iron, low iron, acid, osmosis, and PH) in C. pseudotuberculosis, using a consensus-based network inference algorithm called miRsigand next identified the causal genes in the network using the miRinfluence tool, which is based on the influence diffusion model. We found that over 50% of the genes identified as influential had some essential cellular functions in the genomes. In the strains analyzed, most of the causal genes had crucial roles or participated in processes associated with the response to extracellular stresses, pathogenicity, membrane components, and essential genes. This research brings new insight into the understanding of virulence and infection by C. pseudotuberculosis.

Synergistic interaction of diclofenac and its metabolites with selected antibiotics and amygdalin in wastewaters

Diclofenac (DCF), a non-steroidal anti-inflammatory drug (NSAID) belongs to one of the most frequently detected pharmaceutical residues in the environment. Little is known on the interactions of DCF as well as its major biodegradation metabolites 4'-OHDCF and 5-OHDCF with chemical compounds found in wastewater, including antibiotics such as ampicillin and kanamycin. In the present work we examined the potential interactions between DCF, its metabolites 4'-OHDCF and 5-OHDCF and ampicyllin and kanamycin. We also measured the effect of the mixture of DCF with natural compound - amygdalin. We evaluated the following parameters: E. coli K-12 cells viability, growth inhibition of E. coli K-12 culture, genotoxicity, oxidative stress parameters: sodA promoter induction and ROS generation. The reactivity of E. coli SM recA:luxCDABE biosensor strain in wastewaters matrices contaminated with DCF and kanamycin was also monitored. Obtained results indicated that used antibiotics (ampicyllin, kanamycin) enhanced the toxic effect of DCF used individually and in the mixtures with its metabolites 4'-OHDCF and 5-OHDCF toward E. coli. Similar effect was also obtained in genotoxicity assay. The oxidative stress assays revealed that the highest level of ROS generation and sodA promoter induction were obtained also for the mixtures of DCF, its metabolites with antibiotics. It was also showed that amygdalin influenced the activity of DCF and its biodegradation metabolites. The strongest luminescence response of E. coli SM biosensor strain with recA:luxCDABE genetic construct in filtered treated wastewaters, comparable to control sample was noticed. Obtained results showed that DCF and its biodegradation metabolites 4'-OHDCF and 5-OHDCF can interact with tested antibiotics and compounds of natural origin, i.e. amygdalin to form mixtures showing stronger antimicrobial activity against E. coli than parent chemicals. Moreover the assays in wastewater matrices revealed that E. coli SM recA:luxCDABE biosensor strains is a good tool for bacteria monitoring in wastewater environments.

The study of biological activity of transformation products of diclofenac and its interaction with chlorogenic acid

In the present work we compared the biological activity of DCF, 4'-OHDCF and 5-OHDCF as molecules of most biodegradation pathways of DCF and selected transformation products (2-hydroxyphenylacetic acid; 2,5-dihydroxyphenylacetic acid and 2,6-dichloroaniline) which are produced during AOPs, such as ozonation and UV/H₂O₂. We also examined the interaction of DCF with chlorogenic acid (CGA). CGA is commonly used in human diet and entering the environment along with waste mainly from the processing and brewing of coffee and it can be toxic for microorganisms included in activated sludge. In the present experiment the evaluation of following parameters was performed: E. coli K-12 cells viability, growth inhibition of E. coli K-12 culture, LC₅₀ and mortality of Chironomus aprilinus, genotoxicity, sodA promoter induction and ROS generation. In addition the reactivity of E. coli SM recA:luxCDABE biosensor strain in wastewater matrices was measured. The results showed the influence of DCF, 4'-OHDCF and 5-OHDCF on E. coli K-12 cells viability and bacteria growth, comparable to AOPs by-products. The highest toxicity was observed for selected, tested AOPs by-products, in comparison to the DCF, 4'-OHDCF and 5-OHDCF. Genotoxicity assay indicated that 2,6-dichloroaniline (AOPs by-product) had the highest toxic effect. The oxidative stress assays revealed that the highest level of ROS generation and sodA promoter induction were obtained for DCF, 4'-OHDCF and 5-OHDCF, compared to other tested compounds. We have also found that there is an interaction between chlorogenic acid and DCF, which resulted in increased toxicity of the mixture of the both compounds to E. coli K-12, comparable to parent chemicals. The strongest response of E. coli SM biosensor strain with recA:luxCDABE genetic construct in filtered treated wastewaters, comparable to control sample was noticed. It indicates, that E. coli SM recA:luxCDABE biosensor strains is a good tool for bacteria monitoring in wastewater environment. Due to toxicity and biological activity of tested DCF transformation products, there is a need to use additional wastewater treatment systems for wastewater contaminated with pharmaceutical residues.

The effect of reactive oxygen species (ROS) and ROS-scavenging enzymes, superoxide dismutase and catalase, on the thermotolerant ability of Corynebacterium glutamicum

The function of two reactive oxygen species (ROS) scavenging enzymes, superoxide dismutase (SOD) and catalase, on the thermotolerant ability of Corynebacterium glutamicum was investigated. In this study, the elevation of the growth temperature was shown to lead an increased intracellular ROS for two strains of Corynebacterium glutamicum, the wild-type (KY9002) and the temperature-sensitive mutant (KY9714). In order to examine the effects of ROS-scavenging enzymes on cell growth, either the SOD or the catalase gene was disrupted or overexpressed in KY9002 and KY9714. In the case of the KY9714 strain, it was shown that the disruption of SOD and catalase disturbs cell growth, while the over-productions of both the enzymes enhances cell growth with a growth temperature of 30 °C and 33 °C. Whereas, in the relatively thermotolerant KY9002 strain, the disruption of both enzymes exhibited growth defects more intensively at higher growth temperatures (37 °C or 39 °C), while the overexpression of at least SOD enhanced the cell growth at higher temperatures. Based on the correlation between the cell growth and ROS level, it was suggested that impairment of cell growth in SOD or catalase-disrupted strains could be a result of an increased ROS level. In contrast, the improvement in cell growth for strains with overexpressed SOD or catalase resulted from a decrease in the ROS level, especially at higher growth temperatures. Thus, SOD and catalase might play a crucial role in the thermotolerant ability of C. glutamicum by reducing ROS-induced temperature stress from higher growth temperatures.

Biotypes analysis of Corynebacterium glutamicum growing in dicarboxylic acids demonstrates the existence of industrially-relevant intra-species variations

Production enhancement of industrial microbial products or strains has been traditionally tackled by mutagenesis with chemical methods, irradiation or genetic manipulation. However, the final yield increase must go hand in hand with the resistance increasing against the usual inherent toxicity of the final products. Few studies have been carried out on resistance improvement and even fewer on the initial selection of naturally-generated biotypes, which could decrease the artificial mutagenesis. This fact is vital in the case of GRAS microorganisms as Corynebacterium glutamicum involved in food, feed and cosmetics production. The characteristic wide diversity and plasticity in terms of their genetic material of Actinobacteria eases the biotypes generation. Thus, differences in morphology, glutamate and lysine production and growth in media supplemented with dicarboxylic acids were analysed in four biotypes of C. glutamicum ATCC 13032. A 2D-DIGE analysis of these biotypes growing with itaconic acid allowed us to define their differences. Thus, an optimized central metabolism and better protection against the generated stress conditions present the CgL biotype as a suitable platform for production of itaconic acid, which is used as a building block (e.g.: acrylic plastic). This analysis highlights the preliminary biotypes screening as a way to reach optimal industrial productions.

Characterization of OxyR as a negative transcriptional regulator that represses catalase production in Corynebacterium diphtheriae

Corynebacterium diphtheriae and Corynebacterium glutamicum each have one gene (cat) encoding catalase. In-frame Δcat mutants of C. diphtheriae and C. glutamicum were hyper-sensitive to growth inhibition and killing by H(2)O(2). In C. diphtheriae C7(β), both catalase activity and cat transcription decreased ~2-fold during transition from exponential growth to early stationary phase. Prototypic OxyR in Escherichia coli senses oxidative stress and it activates katG transcription and catalase production in response to H(2)O(2). In contrast, exposure of C. diphtheriae C7(β) to H(2)O(2) did not stimulate transcription of cat. OxyR from C. diphtheriae and C. glutamicum have 52% similarity with E. coli OxyR and contain homologs of the two cysteine residues involved in H(2)O(2) sensing by E. coli OxyR. In-frame ΔoxyR deletion mutants of C. diphtheriae C7(β), C. diphtheriae NCTC13129, and C. glutamicum were much more resistant than their parental wild type strains to growth inhibition by H(2)O(2). In the C. diphtheriae C7(β) ΔoxyR mutant, cat transcripts were about 8-fold more abundant and catalase activity was about 20-fold greater than in the C7(β) wild type strain. The oxyR gene from C. diphtheriae or C. glutamicum, but not from E. coli, complemented the defect in ΔoxyR mutants of C. diphtheriae and C. glutamicum and decreased their H(2)O(2) resistance to the level of their parental strains. Gel-mobility shift, DNaseI footprint, and primer extension assays showed that purified OxyR from C. diphtheriae C7(β) bound, in the presence or absence of DTT, to a sequence in the cat promoter region that extends from nucleotide position -55 to -10 with respect to the +1 nucleotide in the cat ORF. These results demonstrate that OxyR from C. diphtheriae or C. glutamicum functions as a transcriptional repressor of the cat gene by a mechanism that is independent of oxidative stress induced by H(2)O(2).

Kinetic characterisation of recombinant Corynebacterium glutamicum NAD+-dependent LDH over-expressed in E. coli and its rescue of an lldD- phenotype in C. glutamicum: the issue of reversibility re-examined

The ldh gene of Corynebacterium glutamicum ATCC 13032 (gene symbol cg3219, encoding a 314 residue NAD+-dependent L-(+)-lactate dehydrogenase, EC 1.1.1.27) was cloned into the expression vector pKK388-1 and over-expressed in an ldhA-null E. coli TG1 strain upon isopropyl-β-D-thiogalactopyranoside (IPTG) induction. The recombinant protein (referred to here as CgLDH) was purified by a combination of dye-ligand and ion-exchange chromatography. Though active in its absence, CgLDH activity is enhanced 17- to 20-fold in the presence of the allosteric activator D-fructose-1,6-bisphosphate (Fru-1,6-P2). Contrary to a previous report, CgLDH has readily measurable reaction rates in both directions, with Vmax for the reduction of pyruvate being approximately tenfold that of the value for L-lactate oxidation at pH 7.5. No deviation from Michaelis-Menten kinetics was observed in the presence of Fru-1,6-P2, while a sigmoidal response (indicative of positive cooperativity) was seen towards L-lactate without Fru-1,6-P2. Strikingly, when introduced into an lldD- strain of C. glutamicum, constitutively expressed CgLDH enables the organism to grow on L-lactate as the sole carbon source.

The complete genome sequence of Corynebacterium pseudotuberculosis FRC41 isolated from a 12-year-old girl with necrotizing lymphadenitis reveals insights into gene-regulatory networks contributing to virulence

BACKGROUND

Corynebacterium pseudotuberculosis is generally regarded as an important animal pathogen that rarely infects humans. Clinical strains are occasionally recovered from human cases of lymphadenitis, such as C. pseudotuberculosis FRC41 that was isolated from the inguinal lymph node of a 12-year-old girl with necrotizing lymphadenitis. To detect potential virulence factors and corresponding gene-regulatory networks in this human isolate, the genome sequence of C. pseudotuberculosis FCR41 was determined by pyrosequencing and functionally annotated.

RESULTS

Sequencing and assembly of the C. pseudotuberculosis FRC41 genome yielded a circular chromosome with a size of 2,337,913 bp and a mean G+C content of 52.2%. Specific gene sets associated with iron and zinc homeostasis were detected among the 2,110 predicted protein-coding regions and integrated into a gene-regulatory network that is linked with both the central metabolism and the oxidative stress response of FRC41. Two gene clusters encode proteins involved in the sortase-mediated polymerization of adhesive pili that can probably mediate the adherence to host tissue to facilitate additional ligand-receptor interactions and the delivery of virulence factors. The prominent virulence factors phospholipase D (Pld) and corynebacterial protease CP40 are encoded in the genome of this human isolate. The genome annotation revealed additional serine proteases, neuraminidase H, nitric oxide reductase, an invasion-associated protein, and acyl-CoA carboxylase subunits involved in mycolic acid biosynthesis as potential virulence factors. The cAMP-sensing transcription regulator GlxR plays a key role in controlling the expression of several genes contributing to virulence.

CONCLUSION

The functional data deduced from the genome sequencing and the extended knowledge of virulence factors indicate that the human isolate C. pseudotuberculosis FRC41 is equipped with a distinct gene set promoting its survival under unfavorable environmental conditions encountered in the mammalian host.

Identification of a stress-induced factor of Corynebacterineae that is involved in the regulation of the outer membrane lipid composition

Corynebacterineae are gram-positive bacteria that possess a true outer membrane composed of mycolic acids and other lipids. Little is known concerning the modulation of mycolic acid composition and content in response to changes in the bacterial environment, especially temperature variations. To address this question, we investigated the function of the Rv3802c gene, a gene conserved in Corynebacterineae and located within a gene cluster involved in mycolic acid biosynthesis. We showed that the Rv3802 ortholog is essential in Mycobacterium smegmatis, while its Corynebacterium glutamicum ortholog, NCgl2775, is not. We provided evidence that the NCgl2775 gene is transcriptionally induced under heat stress conditions, and while the corresponding protein has no detectable activity under normal growth conditions, the increase in its expression triggers an increase in mycolic acid biosynthesis concomitant with a decrease in phospholipid content. We demonstrated that these lipid modifications are part of a larger outer membrane remodeling that occurs in response to exposure to a moderately elevated temperature (42 degrees C). In addition to showing an increase in the ratio of saturated corynomycolates to unsaturated corynomycolates, our results strongly suggested that the balance between mycolic acids and phospholipids is modified inside the outer membrane following a heat challenge. Furthermore, we showed that these lipid modifications help the bacteria to protect against heat damage. The NCgl2775 protein and its orthologs thus appear to be a protein family that plays a role in the regulation of the outer membrane lipid composition of Corynebacterineae under stress conditions. We therefore propose to name this protein family the envelope lipids regulation factor (ElrF) family.

Regulation of ldh expression during biotin-limited growth of Corynebacterium glutamicum

Corynebacterium glutamicum is a biotin-auxotrophic bacterium and some strains efficiently produce glutamic acid under biotin-limiting conditions. In an effort to understand C. glutamicum metabolism under biotin limitation, growth of the type strain ATCC 13032 was investigated in batch cultures and a time-course analysis was performed. A transient excretion of organic acids was observed and we focused our attention on lactate synthesis. Lactate synthesis was due to the ldh-encoded l-lactate dehydrogenase (Ldh). Features of Ldh activity and ldh transcription were analysed. The ldh gene was shown to be regulated at the transcriptional level by SugR, a pleiotropic transcriptional repressor also acting on most phosphotransferase system (PTS) genes. Electrophoretic mobility shift assays (EMSAs) and site-directed mutagenesis allowed the identification of the SugR-binding site. Effector studies using EMSAs and analysis of ldh expression in a ptsF mutant revealed fructose 1-phosphate as a highly efficient negative effector of SugR. Fructose 1,6-bisphosphate also affected SugR binding.

Stationary phase mutagenesis in B. subtilis: a paradigm to study genetic diversity programs in cells under stress

One of the experimental platforms to study programs increasing genetic diversity in cells under stressful or nondividing conditions is adaptive mutagenesis, also called stationary phase mutagenesis or stress-induced mutagenesis. In some model systems, there is evidence that mutagenesis occurs in genes that are actively transcribed. Some of those genes may be actively transcribed as a result of environmental stress giving the appearance of directed mutation. That is, cells under conditions of starvation or other stresses accumulate mutations in transcribed genes, including those transcribed because of the selective pressure. An important question concerns how, within the context of stochastic processes, a cell biases mutation to genes under selection pressure? Because the mechanisms underlying DNA transactions in prokaryotic cells are well conserved among the three domains of life, these studies are likely to apply to the examination of genetic programs in eukaryotes. In eukaryotes, increasing genetic diversity in differentiated cells has been implicated in neoplasia and cell aging. Historically, Escherichia coli has been the paradigm used to discern the cellular processes driving the generation of adaptive mutations; however, examining adaptive mutation in Bacillus subtilis has contributed new insights. One noteworthy contribution is that the B. subtilis' ability to accumulate chromosomal mutations under conditions of starvation is influenced by cell differentiation and transcriptional derepression, as well as by proteins homologous to transcription and repair factors. Here we revise and discuss concepts pertaining to genetic programs that increase diversity in B. subtilis cells under nutritional stress.

Corynebacterium glutamicum superoxide dismutase is a manganese-strict non-cambialistic enzyme in vitro

Superoxide dismutase (SOD) of Corynebacterium glutamicum was purified and characterized. The enzyme had a native molecular weight of about 80kDa, whereas a monomer with molecular weight of 24kDa was found on SDS-PAGE suggesting it to be homotetramer. The native SOD activity stained gel revealed a unique cytosolic enzyme. Supplementing growth media with manganese increased the specific activity significantly, while adding iron did not result in significant difference. No growth perturbation was observed with the supplemented media. In vitro metal removal and replacement studies revealed conservation of about 85% of the specific activity by substitution with manganese, while substitution with copper, iron, nickel or zinc did not restore any significant specific activity. Manganese was identified by atomic absorption spectrometer, while no signals corresponding to fixing other metallic elements were detected. Thus, C. glutamicum SOD could be considered a strict (non-cambialistic) manganese superoxide dismutase (MnSOD).

Mn/Fe superoxide dismutase interaction fingerprints and prediction of oligomerization and metal cofactor from sequence

Fe- and Mn-containing superoxide dismutase (sod) enzymes are closely related and similar in both amino acid sequence and structure, but differ in their mode of oligomerization and in their specificity for the Fe or Mn cofactor. The goal of the present work is to identify and analyze the sequence and structure characteristics that ensure the cofactor specificities and the oligomerization modes. For that purpose, 374 sod sequences and 17 sod crystal structures were collected and aligned. These alignments were searched for residues and inter-residue interactions that are conserved within the whole sod family, or alternatively, that are specific to a given sod subfamily sharing common characteristics. This led us to define key residues and inter-residue interaction fingerprints in each subfamily. The comparison of these fingerprints allows, on a rational basis, the design of mutants likely to modulate the activity and/or specificity of the target sod, in good agreement with the available experimental results on known mutants. The key residues and interaction fingerprints are furthermore used to predict if a novel sequence corresponds to a sod enzyme, and if so, what type of sod it is. The predictions of this fingerprint method reach much higher scores and present much more discriminative power than the commonly used method that uses pairwise sequence comparisons.

Gene expression systems in corynebacteria

Corynebacterium belongs to a group of gram-positive bacteria having moderate to high G+C content, the other members being Mycobacterium, Nocardia, and Rhodococcus. Considerable information is now available on the plasmids, gene regulatory elements, and gene expression in corynebacteria, especially in soil corynebacteria such as Corynebacterium glutamicum. These bacteria are non-pathogenic and, unlike Bacillus and Streptomyces, are low in proteolytic activity and thus have the potential of becoming attractive systems for expression of heterologous proteins. This review discusses recent advances in our understanding of the organization of various regulatory elements, such as promoters, transcription terminators, and development of vectors for cloning and gene expression.

Cloning and characterization of antioxidant enzyme methionine sulfoxide-S-reductase from Caenorhabditis elegans

Methionine (Met) residues in proteins are susceptible to oxidation. The resulting methionine sulfoxide can be reduced back to methionine by methionine sulfoxide-S-reductase (MsrA). The MsrA gene, isolated from Caenorhabditis elegans, was cloned and expressed in Escherichia coli. The resultant enzyme was able to revert both free Met and Met in proteins in the presence of either NADPH or dithiothreitol (DTT). However, approximately seven times higher enzyme activity was observed in the presence of DTT than of NADPH. The enzyme had an absolute specificity for the reduction of l-methionine-S-sulfoxide but no specificity for the R isomer. K(m) and k(cat) values for the enzyme were approximately 1.18 mM and 3.64 min(-1), respectively. Other kinetics properties of the enzyme were also evaluated.

Inhibitor-associated transposition events in Corynebacterium glutamicum

In up to 100% of all bacteria grown in the presence of initially inhibitory concentrations of five diverse inhibitors, an extra copy of the resident insertion element IS 31831 was found in specific chromosomal regions, the sites of which apparently depended on the inhibitor used. Thus, in nine out of nine independently isolated cyanide-associated transpositions, the acquired copy was located within an ORF encoding a protein related to the hypothetical but conserved protein YeiH of Escherichia coli. A putative Sox box upstream of the yeiH gene implicates superoxide as a potential regulator of the gene, a possibility further supported by the finding that superoxide dismutase (SodA) is overexpressed in cells cultured in cyanide-containing medium. Neither the cyanide-associated nor any of the other transposition mutations appeared to confer any discernible phenotypic advantage upon cells grown in the presence or absence of the inhibitors, as revealed most stringently by mixed-cell experiments. An alternative, albeit heterodox, explanation for the emergence of the mutants postulates a very high rate of transpositional activity in the presence of inhibitors. The initial emergence of the mutants was found to depend crucially upon the cell density. Thus, when growth medium was supplemented with 50 mM fluoropyruvate and inoculated to a density of 2 x 10(7) cfu/ml, single colonies with heterogeneous restriction fragment length polymorphisms (RFLPs) were routinely isolated at a frequency of 6 to 16% after 1-2 days of incubation. After 3 days, 10-36% of the colonies showed RFLPs, but the type was now dominated by the fluoropyruvate-specific RFLP, which, at higher resolution, invariably proved to be heterogeneous. This heterogeneity proved that these specific mutants were of multiple origin, indicating that clonal enrichment was irrelevant to their emergence. It is suggested that the presence of the inhibitor induces the development of hyper-transpositional activity, which is regulated by a soluble bacterial product.

Promoters of Corynebacterium glutamicum

Regulation of gene expression in Corynebacterium glutamicum represents an important issue since this Gram-positive bacterium is a notable industrial amino acid producer. Transcription initiation, beginning by binding of RNA polymerase to the promoter DNA sequence, is one of the main points at which bacterial gene expression is regulated. More than 50 transcriptional promoters have so far been experimentally localized in C. glutamicum. Most of them are assumed to be promoters of vegetative genes recognized by the main sigma factor. Although transcription initiation rate defined by many of these promoters may be affected by transcription factors, which activate or repress their function, the promoter regions share common sequence features, which may be generalized in a consensus sequence. In the consensus C. glutamicum promoter, the prominent feature is a conserved extended -10 region tgngnTA(c/t)aaTgg, while the -35 region is much less conserved. Some commonly utilized heterologous promoters were shown to drive strong gene expression in C. glutamicum. Conversely, some C. glutamicum promoters were found to function in Escherichia coli and in other bacteria. These observations suggest that C. glutamicum promoters functionally conform with the common bacterial promoter scheme, although they differ in some sequence structures.

Differential expression and localization of Mn and Fe superoxide dismutases in the heterocystous cyanobacterium Anabaena sp. strain PCC 7120

Superoxide dismutases (Sods) play very important roles in preventing oxidative damages in aerobic organisms. The nitrogen-fixing heterocystous cyanobacterium Anabaena sp. strain PCC 7120 has two Sod-encoding genes: a sodB, encoding a soluble iron-containing Sod (FeSod), and a sodA, encoding a manganese-containing Sod (MnSod). The FeSod was purified and characterized. A recombinant FeSod was also obtained by overproduction in Escherichia coli. Immunoblot study of the FeSod during induction of heterocyst differentiation showed that the cells produced six- to eightfold more FeSod 8 h after a shift from a nitrogen-replete condition to a nitrogen-depleted condition. However, the amount of FeSod protein in filaments with mature heterocysts was the same as that in filaments grown with combined nitrogen. Superoxide anion-generating chemicals such as methyl viologen did not induce upregulation of the sodB gene expression. The predicted preprotein of the sodA gene has a leader peptide and a motif for membrane attachment at the N terminus of the mature protein. Activity staining after gel electrophoresis of the purified thylakoid membranes showed that most of the MnSod in Anabaena sp. strain PCC 7120 was located on thylakoids toward the lumenal side. Expression of the sodA gene in E. coli shows that the leader peptide was required for its activity and the membrane localization of the MnSod. Northern hybridization detected one 0.82-kb transcript of sodA. The sodA gene was upregulated by methyl viologen, whereas its amount was unchanged during heterocyst differentiation. Immunoblotting and activity staining showed that isolated heterocysts contained a lower but still significant amount of FeSod, suggesting that its function is required in heterocysts. No MnSod was observed in isolated heterocysts. These results show that the two different Sod proteins have differentiated roles in Anabaena sp. strain PCC 7120.

The superoxide dismutase gene sodM is unique to Staphylococcus aureus: absence of sodM in coagulase-negative staphylococci

Superoxide dismutase (SOD) profiles of clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci (CoNS) were determined by using whole-cell lysates and activity gels. All S. aureus clinical isolates exhibited three closely migrating bands of activity as previously determined for laboratory strains of S. aureus: SodM, SodA, and a hybrid composed of SodM and SodA (M. W. Valderas and M. E. Hart, J. Bacteriol. 183:3399-3407, 2001). In contrast, the CoNS produced only one SOD activity, which migrated similarly to SodA of S. aureus. Southern analysis of eight CoNS species identified only a single sod gene in each case. A full-length sod gene was cloned from Staphylococcus epidermidis and determined to be more similar to sodA than to sodM of S. aureus. Therefore, this gene was designated sodA. The deduced amino acid sequence of the S. epidermidis sodA was 92 and 76% identical to that of the SodA and SodM proteins of S. aureus, respectively. The S. epidermidis sodA gene expressed from a plasmid complemented a sodA mutation in S. aureus, and the protein formed a hybrid with SodM of S. aureus. Both hybrid SOD forms as well as the SodM and SodA proteins of S. aureus and the S. epidermidis SodA protein exist as dimers. These data indicate that sodM is found only in S. aureus and not in the CoNS, suggesting an important divergence in the evolution of this genus and a unique role for SodM in S. aureus.

Inactivation of the Moraxella catarrhalis superoxide dismutase SodA induces constitutive expression of iron-repressible outer membrane proteins

Many pathogens produce one or more superoxide dismutases (SODs), enzymes involved in the detoxification of endogenous and exogenous reactive oxygen species that are encountered during the infection process. One detectable cytoplasmic SOD was identified in the human mucosal pathogen Moraxella catarrhalis, and the gene responsible for the SOD activity, sodA, was isolated from a recent pediatric clinical isolate (strain 7169). Sequence analysis of the cloned M. catarrhalis 7169 DNA fragment revealed an open reading frame of 618 bp encoding a polypeptide of 205 amino acids with 48 to 67% identity to known bacterial manganese-cofactored SODs. An isogenic M. catarrhalis sodA mutant was constructed in strain 7169 by allelic exchange. In contrast to the wild-type 7169, the 7169::sodK20 mutant was severely attenuated for aerobic growth, even in rich medium containing supplemental amino acids, and exhibited extreme sensitivity to the redox-active agent methyl viologen. The ability of recombinant SodA to rescue the aerobic growth defects of E. coli QC774, a sodA sodB-deficient mutant, demonstrated the functional expression of SOD activity by cloned M. catarrhalis sodA. Indirect SOD detection assays were used to visualize both native and recombinant SodA activity in bacterial lysates. This study demonstrates that M. catarrhalis SodA plays a critical role in the detoxification of endogenous, metabolically produced oxygen radicals. In addition, the outer membrane protein (OMP) profile of 7169::sodK20 was consistent with iron starvation in spite of growth under iron-replete conditions. This novel observation indicates that M. catarrhalis strains lacking SodA constitutively express immunogenic OMPs previously described as iron repressible, and this potentially attenuated mutant strain may be an attractive vaccine candidate.

Lipoamide dehydrogenase from Corynebacterium glutamicum: molecular and physiological analysis of the lpd gene and characterization of the enzyme

Lipoamide dehydrogenase (LPD) is an essential component of the pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase complexes, both playing a crucial role within the central metabolism of aerobic organisms. Using oligonucleotides designed according to conserved regions of LPD amino acid sequences from several organisms, the lpd gene from Corynebacterium glutamicum was identified and subsequently subcloned. The cloned lpd gene expressed in C. glutamicum cells harbouring the gene on a plasmid showed a 12-fold higher specific LPD activity when compared to the wild-type strain. DNA sequence analysis of a 4524 bp segment containing the lpd gene and adjacent regions revealed that the lpd gene is not flanked by genes encoding other subunits of the pyruvate or 2-oxoglutarate dehydrogenase complexes and predicted an LPD polypeptide of 469 amino acids with an M(r) of 50619. The amino acid sequence of this polypeptide shows between 26 and 58% identity when compared to LPD enzymes from other organisms. Transcriptional analyses revealed that the lpd gene from C. glutamicum is monocistronic (1.45 kb mRNA) and that its transcription is initiated exactly at the nucleotide defined as the translational start. LPD was purified and biochemically characterized. This analysis revealed that the enzyme catalyses the reversible reoxidation of dihydrolipoic acid and NADH:NAD(+) transhydrogenation, and is able to transfer electrons from NADH to various redox-active compounds and quinones. An in vivo participation of C. glutamicum LPD in facilitation of quinone redox cycling is proposed.