Characterization of methylglyoxal synthase from Clostridium acetobutylicum ATCC 824 and its use in the formation of 1, 2-propanediol

Methylglyoxal Formation-Metabolic Routes and Consequences

Methylglyoxal (MGO), a by-product of glycolysis, plays a significant role in cellular metabolism, particularly under stress conditions. However, MGO is a potent glycotoxin, and its accumulation has been linked to the development of several pathological conditions due to oxidative stress, including diabetes mellitus and neurodegenerative diseases. This paper focuses on the biochemical mechanisms by which MGO contributes to oxidative stress, particularly through the formation of advanced glycation end products (AGEs), its interactions with antioxidant systems, and its involvement in chronic diseases like diabetes, neurodegeneration, and cardiovascular disorders. MGO exerts its effects through multiple signaling pathways, including NF-κB, MAPK, and Nrf2, which induce oxidative stress. Additionally, MGO triggers apoptosis primarily via intrinsic and extrinsic pathways, while endoplasmic reticulum (ER) stress is mediated through PERK-eIF2α and IRE1-JNK signaling. Moreover, the activation of inflammatory pathways, particularly through RAGE and NF-κB, plays a crucial role in the pathogenesis of these conditions. This study points out the connection between oxidative and carbonyl stress due to increased MGO formation, and it should be an incentive to search for a marker that could have prognostic significance or could be a targeted therapeutic intervention in various diseases.

The possible role of methylglyoxal metabolism in cancer

Tumours reprogram their metabolism to acquire an evolutionary advantage over normal cells. However, not all such metabolic pathways support energy production. An example of these metabolic pathways is the Methylglyoxal (MG) one. This pathway helps maintain the redox state, and it might act as a phosphate sensor that monitors the intracellular phosphate levels. In this work, we discuss the biochemical step of the MG pathway and interrelate it with cancer.

Recent advances in microbial biosynthesis of C3 - C5 diols: Genetics and process engineering approaches

Diols derived from renewable feedstocks have significant commercial interest in polymer, pharmaceutical, cosmetics, flavors and fragrances, food and feed industries. In C3-C5 diols biological processes of 1,3-propanediol, 1,2-propanediol and 2,3-butanediol have been commercialized as other isomers are non-natural metabolites and lack natural biosynthetic pathways. However, the developments in the field of systems and synthetic biology paved a new path to learn, build, construct, and test for efficient chassis strains. The current review addresses the recent advancements in metabolic engineering, construction of novel pathways, process developments aimed at enhancing in production of C3-C5 diols. The requisites on developing an efficient and sustainable commercial bioprocess for C3-C5 diols were also discussed.

Elucidation of antifungal and aflatoxin B1 inhibitory mode of action of Eugenia caryophyllata L. essential oil loaded chitosan nanomatrix against Aspergillus flavus

The present study investigated the novel antifungal, and anti-aflatoxin B₁ mechanism of Eugenia caryophyllata L. essential oil (ECEO) loaded chitosan nanomatrix against the toxigenic strain of A. flavus (AFLV-DK-02). Phytochemical profiling of ECEO was done by GC-MS which revealed eugenol (73.6%) as the primary bioactive compound. ECEO was encapsulated inside the chitosan nanomatrix (ECEO-Np) and characterized using SEM, AFM, FTIR and XRD analysis. The ECEO-Np exhibited enhance antifungal (0.25 μL/mL) and anti-aflatoxin B₁ inhibitory activity (0.15 μL/mL) than ECEO. Antifungal and antiaflatoxin B₁ inhibitory activity was found to be related with impairment in the biological functioning of the plasma membrane (ergosterol synthesis, leakage of membrane ions, UV light (260, 280 nm) absorbing material, dead cell by propidium iodide assay, mitochondrial membrane potential (MMP), methylglyoxal and inhibition in essential carbon substrate utilization). ECEO-Np exhibited remarkable free radical scavenging activity with IC₅₀ value of 0.002 μL/mL. ECEO-Np effectively preserves the sensory characteristics of exposed maize crop seed up to six months of storage and shows considerable safety profile (non-toxic, non-mutagenic, non-hepatotoxic, non-carcinogenic, non-tumorigenic and biodegradable) using computational ADMET (absorption, distribution, metabolism, excretion, and toxicity) analysis.

A novel hyperthermophilic methylglyoxal synthase: molecular dynamic analysis on the regional fluctuations

Two putative methylglyoxal synthases, which catalyze the conversion of dihydroxyacetone phosphate to methylglyoxal, from Oceanithermus profundus DSM 14,977 and Clostridium difficile 630 have been characterized for activity and thermal stability. The enzyme from O. profundus was found to be hyperthermophilic, with the optimum activity at 80 °C and the residual activity up to 59% after incubation of 15 min at 95 °C, whereas the enzyme from C. difficile was mesophilic with the optimum activity at 40 °C and the residual activity less than 50% after the incubation at 55 °C or higher temperatures for 15 min. The structural analysis of the enzymes with molecular dynamics simulation indicated that the hyperthermophilic methylglyoxal synthase has a rigid protein structure with a lower overall root-mean-square-deviation value compared with the mesophilic or thermophilic counterparts. In addition, the simulation results identified distinct regions with high fluctuations throughout those of the mesophilic or thermophilic counterparts via root-mean-square-fluctuation analysis. Specific molecular interactions focusing on the hydrogen bonds and salt bridges in the distinct regions were analyzed in terms of interatomic distances and positions of the individual residues with respect to the secondary structures of the enzyme. Key interactions including specific salt bridges and hydrogen bonds between a rigid beta-sheet core and surrounding alpha helices were found to contribute to the stabilisation of the hyperthermophilic enzyme by reducing the regional fluctuations in the protein structure. The structural information and analysis approach in this study can be further exploited for the engineering and industrial application of the enzyme.

The Glyoxalase System-New Insights into an Ancient Metabolism

The glyoxalase system was discovered over a hundred years ago and since then it has been claimed to provide the role of an indispensable enzyme system in order to protect cells from a toxic byproduct of glycolysis. This review gives a broad overview of what has been postulated in the last 30 years of glyoxalase research, but within this context it also challenges the concept that the glyoxalase system is an exclusive tool of detoxification and that its substrate, methylglyoxal, is solely a detrimental burden for every living cell due to its toxicity. An overview of consequences of a complete loss of the glyoxalase system in various model organisms is presented with an emphasis on the role of alternative detoxification pathways of methylglyoxal. Furthermore, this review focuses on the overlooked posttranslational modification of Glyoxalase 1 and its possible implications for cellular maintenance under various (patho-)physiological conditions. As a final note, an intriguing point of view for the substrate methylglyoxal is offered, the concept of methylglyoxal (MG)-mediated hormesis.

Developing Clostridium diolis as a biorefinery chassis by genetic manipulation

Clostridium diolis can efficiently utilize various inexpensive, renewable resources such as crude glycerol and lignocellulosic biomass hydrolysate to produce bulk chemicals and fuels. However, its study has been impeded by the lack of efficient plasmids electro-transformation techniques. In this study, an efficient electroporation protocol for C. diolis was developed and two replicons functional in C. diolis were identified. After optimizing parameters, the electro-transformation efficiency was enhanced from 5 to 692 transformants/ug DNA. Moreover, metabolic engineering of C. diolis was performed as proof of concept for the first time. By simply overexpressing heterologous genes based on the replicable plasmids, the strain was engineered to improve productions of diol (1,3-propanediol) and n-alcohol (butanol), and to enable butyl acetate synthesis in vivo, respectively under different culture conditions. This work represented a milestone of breeding C. diolis using metabolic engineering, and paved the way for studying C. diolis on the molecular level.

Crystal Structure and Biophysical Analysis of Furfural-Detoxifying Aldehyde Reductase from Clostridium beijerinckii

Many aldehydes, such as furfural, are present in high quantities in lignocellulose lysates and are fermentation inhibitors, which makes biofuel production from this abundant carbon source extremely challenging. Cbei_3974 has recently been identified as an aldo-keto reductase responsible for partial furfural resistance in Clostridium beijerinckii Rational engineering of this enzyme could enhance the furfural tolerance of this organism, thereby improving biofuel yields. We report an extensive characterization of Cbei_3974 and a single-crystal X-ray structure of Cbei_3974 in complex with NADPH at a resolution of 1.75 Å. Docking studies identified residues involved in substrate binding, and an activity screen revealed the substrate tolerance of the enzyme. Hydride transfer, which is partially rate limiting under physiological conditions, occurs from the pro-R hydrogen of NADPH. Enzyme isotope labeling revealed a temperature-independent enzyme isotope effect of unity, indicating that the enzyme does not use dynamic coupling for catalysis and suggesting that the active site of the enzyme is optimally configured for catalysis with the substrate tested.IMPORTANCE Here we report the crystal structure and biophysical properties of an aldehyde reductase that can detoxify furfural, a common inhibitor of biofuel fermentation found in lignocellulose lysates. The data contained here will serve as a guide for protein engineers to develop improved enzyme variants that would impart furfural resistance to the microorganisms used in biofuel production and thus lead to enhanced biofuel yields from this sustainable resource.

The skin microbiome of vertebrates

The skin constitutes the primary physical barrier between vertebrates and their external environment. Characterization of skin microorganisms is essential for understanding how a host evolves in association with its microbial symbionts, modeling immune system development, diagnosing illnesses, and exploring the origins of potential zoonoses that affect humans. Although many studies have characterized the human microbiome with culture-independent techniques, far less is known about the skin microbiome of other mammals, amphibians, birds, fish, and reptiles. The aim of this review is to summarize studies that have leveraged high-throughput sequencing to better understand the skin microorganisms that associate with members of classes within the subphylum Vertebrata. Specifically, links will be explored between the skin microbiome and vertebrate characteristics, including geographic location, biological sex, animal interactions, diet, captivity, maternal transfer, and disease. Recent literature on parallel patterns between host evolutionary history and their skin microbial communities, or phylosymbiosis, will also be analyzed. These factors must be considered when designing future microbiome studies to ensure that the conclusions drawn from basic research translate into useful applications, such as probiotics and successful conservation strategies for endangered and threatened animals.

Structural basis for the regulatory interaction of the methylglyoxal synthase MgsA with the carbon flux regulator Crh in

Utilization of energy-rich carbon sources such as glucose is fundamental to the evolutionary success of bacteria. Glucose can be catabolized via glycolysis for feeding the intermediary metabolism. The methylglyoxal synthase MgsA produces methylglyoxal from the glycolytic intermediate dihydroxyacetone phosphate. Methylglyoxal is toxic, requiring stringent regulation of MgsA activity. In the Gram-positive bacterium Bacillus subtilis, an interaction with the phosphoprotein Crh controls MgsA activity. In the absence of preferred carbon sources, Crh is present in the nonphosphorylated state and binds to and thereby inhibits MgsA. To better understand the mechanism of regulation of MgsA, here we performed biochemical and structural analyses of B. subtilis MgsA and of its interaction with Crh. Our results indicated that MgsA forms a hexamer (i.e. a trimer of dimers) in the crystal structure, whereas it seems to exist in an equilibrium between a dimer and hexamer in solution. In the hexamer, two alternative dimers could be distinguished, but only one appeared to prevail in solution. Further analysis strongly suggested that the hexamer is the biologically active form. In vitro cross-linking studies revealed that Crh interacts with the N-terminal helices of MgsA and that the Crh-MgsA binding inactivates MgsA by distorting and thereby blocking its active site. In summary, our results indicate that dimeric and hexameric MgsA species exist in an equilibrium in solution, that the hexameric species is the active form, and that binding to Crh deforms and blocks the active site in MgsA.

Methylglyoxal synthase regulates cell elongation via alterations of cellular methylglyoxal and spermidine content in Bacillus subtilis

Methylglyoxal regulates cell division and differentiation through its interaction with polyamines. Loss of their biosynthesizing enzyme causes physiological impairment and cell elongation in eukaryotes. However, the reciprocal effects of methylglyoxal and polyamine production and its regulatory metabolic switches on morphological changes in prokaryotes have not been addressed. Here, Bacillus subtilis methylglyoxal synthase (mgsA) and polyamine biosynthesizing genes encoding arginine decarboxylase (SpeA), agmatinase (SpeB), and spermidine synthase (SpeE), were disrupted or overexpressed. Treatment of 0.2mM methylglyoxal and 1mM spermidine led to the elongation and shortening of B. subtilis wild-type cells to 12.38±3.21μm (P<0.05) and 3.24±0.73μm (P<0.01), respectively, compared to untreated cells (5.72±0.68μm). mgsA-deficient (mgsA^-) and -overexpressing (mgsA^OE) mutants also demonstrated cell shortening and elongation, similar to speB- and speE-deficient (speB^- and speE^-) and -overexpressing (speB^OE and speE^OE) mutants. Importantly, both mgsA-depleted speB^OE and speE^OE mutants (speB^OE/mgsA^- and speE^OE/mgsA^-) were drastically shortened to 24.5% and 23.8% of parental speB^OE and speE^OE mutants, respectively. These phenotypes were associated with reciprocal alterations of mgsA and polyamine transcripts governed by the contents of methylglyoxal and spermidine, which are involved in enzymatic or genetic metabolite-control mechanisms. Additionally, biophysically detected methylglyoxal-spermidine Schiff bases did not affect morphogenesis. Taken together, the findings indicate that methylglyoxal triggers cell elongation. Furthermore, cells with methylglyoxal accumulation commonly exhibit an elongated rod-shaped morphology through upregulation of mgsA, polyamine genes, and the global regulator spx, as well as repression of the cell division and shape regulator, FtsZ.

N5 ,N10 -methylenetetrahydromethanopterin reductase from Methanocaldococcus jannaschii also serves as a methylglyoxal reductase

In Methanocaldococcus jannaschii, methylglyoxal (MG) is required for aromatic amino acid biosynthesis. Previously, the reduction of MG to lactaldehyde in Methanocaldococcus jannaschii cell extracts using either NADPH or F₄₂₀ H₂ was demonstrated; however, the enzyme responsible was not identified. Using NADPH as the reductant, the unknown enzyme was purified from cell extracts of Methanocaldococcus jannaschii and determined to be the F₄₂₀ -dependent N⁵ ,N¹⁰ -methylenetetrahydromethanopterin reductase (Mer). Here, we report that the recombinantly overexpressed Mer is able to use NADPH and MG (K_M of 1.6 and 1.0 mm, respectively) to produce lactaldehyde. Additionally, Mer does not catalyze the reduction of MG to lactaldehyde in the presence of reduced Fo, the precursor of F₄₂₀ .

Disruption of the Reductive 1,3-Propanediol Pathway Triggers Production of 1,2-Propanediol for Sustained Glycerol Fermentation by Clostridium pasteurianum

Crude glycerol, the major by-product of biodiesel production, is an attractive bioprocessing feedstock owing to its abundance, low cost, and high degree of reduction. In line with the advent of the biodiesel industry, Clostridium pasteurianum has gained prominence as a result of its unique capacity to convert waste glycerol into n-butanol, a high-energy biofuel. However, no efforts have been directed at abolishing the production of 1,3-propanediol (1,3-PDO), the chief competing product of C. pasteurianum glycerol fermentation. Here, we report rational metabolic engineering of C. pasteurianum for enhanced n-butanol production through inactivation of the gene encoding 1,3-PDO dehydrogenase (dhaT). In spite of current models of anaerobic glycerol dissimilation, culture growth and glycerol utilization were unaffected in the dhaT disruption mutant (dhaT::Ll.LtrB). Metabolite characterization of the dhaT::Ll.LtrB mutant revealed an 83% decrease in 1,3-PDO production, encompassing the lowest C. pasteurianum 1,3-PDO titer reported to date (0.58 g liter(-1)). With 1,3-PDO formation nearly abolished, glycerol was converted almost exclusively to n-butanol (8.6 g liter(-1)), yielding a high n-butanol selectivity of 0.83 g n-butanol g(-1) of solvents compared to 0.51 g n-butanol g(-1) of solvents for the wild-type strain. Unexpectedly, high-performance liquid chromatography (HPLC) analysis of dhaT::Ll.LtrB mutant culture supernatants identified a metabolite peak consistent with 1,2-propanediol (1,2-PDO), which was confirmed by nuclear magnetic resonance (NMR). Based on these findings, we propose a new model for glycerol dissimilation by C. pasteurianum, whereby the production of 1,3-PDO by the wild-type strain and low levels of both 1,3-PDO and 1,2-PDO by the engineered mutant balance the reducing equivalents generated during cell mass synthesis from glycerol.

IMPORTANCE

Organisms from the genus Clostridium are perhaps the most notable native cellular factories, owing to their vast substrate utilization range and equally diverse variety of metabolites produced. The ability of C. pasteurianum to sustain redox balance and glycerol fermentation despite inactivation of the 1,3-PDO pathway is a testament to the exceptional metabolic flexibility exhibited by clostridia. Moreover, identification of a previously unknown 1,2-PDO-formation pathway, as detailed herein, provides a deeper understanding of fermentative glycerol utilization in clostridia and will inform future metabolic engineering endeavors involving C. pasteurianum To our knowledge, the C. pasteurianum dhaT disruption mutant derived in this study is the only organism that produces both 1,2- and 1,3-PDOs. Most importantly, the engineered strain provides an excellent platform for highly selective production of n-butanol from waste glycerol.

Pi inhibits intracellular accumulation of methylglyoxal in promastigote form of L. donovani

Similar to their mammalian counterpart, protozoan parasites including Leishmania donovani detoxify methylglyoxal (MG),(1) a toxic ubiquitous product generated in glycolysis pathway. However, it differs in one or more way(s) from the humans. It is known that MG is eliminated either through glyoxalase (GLO)(2) pathway and/or excreted across the cell membrane. This toxic metabolic by-product is known to be detoxified predominantly by the GLO pathway and excretion across the cell membrane is never considered to be a significant pathway for its detoxification. We have tried to modulate these pathways under various physiological conditions to find ways that may lead to accumulation of MG in L. donovani. Besides targeting the GLO pathway, we intend to understand the mechanism of MG release across the cell membrane and possible ways to inhibit its exclusion from parasites. In our study, it was found that inorganic phosphate (Pi)(3) in the presence of glucose inhibits the production of MG as well as promotes the expulsion of MG from the cell. Moreover, the trivalent form of antimony (Sb(III)) inhibits GLO pathway and thus detoxification of MG. Inhibition of Pi transport, which is a Na(+)/H(+) dependent process, restores the Pi mediated abrogation of MG production. Thus, Sb(III) along with inhibitors of Pi transporter may be a therapeutic advancement for treatment of antimony resistant cases of human visceral leishmaniasis. However, it requires further validation using specific inhibitor(s) of Pi transporter.

Rationalization of allosteric pathway in Thermus sp. GH5 methylglyoxal synthase

A sequence of 10 amino acids at the C-terminus region of methylglyoxal synthase from Escherichia coli (EMGS) provides an arginine, which plays a crucial role in forming a salt bridge with a proximal aspartate residue in the neighboring subunit, consequently transferring the allosteric signal between subunits. In order to verify the role of arginine, the gene encoding MGS from a thermophile species, Thermus sp. GH5 (TMGS) lacking this arginine was cloned with an additional 30 bp sequence at the 3´-end and then expressed in form of a fusion TMGS with a 10 residual segment at the C-terminus (TMGS(+)). The resulting recombinant enzyme showed a significant increase in cooperativity towards phosphate, reflected by a change in the Hill coefficient (nH) from 1.5 to 1.99. Experiments including site directed mutagenesis for Asp-10 in TMGS and TMGS(+), two dimentional structural survey, fluorescence and irreversible thermoinactivation were carried out to confirm this pathway.

Transcriptional portrait of Actinobacillus pleuropneumoniae during acute disease--potential strategies for survival and persistence in the host

Background

Gene expression profiles of bacteria in their natural hosts can provide novel insight into the host-pathogen interactions and molecular determinants of bacterial infections. In the present study, the transcriptional profile of the porcine lung pathogen Actinobacillus pleuropneumoniae was monitored during the acute phase of infection in its natural host.

Methodology/Principal Findings

Bacterial expression profiles of A. pleuropneumoniae isolated from lung lesions of 25 infected pigs were compared in samples taken 6, 12, 24 and 48 hours post experimental challenge. Within 6 hours, focal, fibrino hemorrhagic lesions could be observed in the pig lungs, indicating that A. pleuropneumoniae had managed to establish itself successfully in the host. We identified 237 differentially regulated genes likely to encode functions required by the bacteria for colonization and survival in the host. This group was dominated by genes involved in various aspects of energy metabolism, especially anaerobic respiration and carbohydrate metabolism. Remodeling of the bacterial envelope and modifications of posttranslational processing of proteins also appeared to be of importance during early infection. The results suggested that A. pleuropneumoniae is using various strategies to increase its fitness, such as applying Na+ pumps as an alternative way of gaining energy. Furthermore, the transcriptional data provided potential clues as to how A. pleuropneumoniae is able to circumvent host immune factors and survive within the hostile environment of host macrophages. This persistence within macrophages may be related to urease activity, mobilization of various stress responses and active evasion of the host defenses by cell surface sialylation.

Conclusions/Significance

The data presented here highlight the importance of metabolic adjustments to host conditions as virulence factors of infecting microorganisms and help to provide insight into the mechanisms behind the efficient colonization and persistence of A. pleuropneumoniae during acute disease.

Cloning, expression, and characterization of a novel methylglyoxal synthase from Thermus sp. strain GH5

A gene encoding methylglyoxal synthase from Thermus sp. GH5 (TMGS) was cloned, sequenced, overexpressed, and purified by Q-Sepharose. The TMGS gene was composed of 399 bp which encoded a polypeptide of 132 amino acids with a molecular mass of 14.3 kDa. The K (m) and k (cat) values of TMGS were 0.56 mM and 325 (s(-1)), respectively. The enzyme exhibited its optimum activity at pH 6 and 75 degrees C. Comparing the amino acid sequences and Hill coefficients of Escherichia coli MGS and TMGS revealed that the loss of Arg 150 in TMGS has caused a decrease in the cooperativity between the enzyme subunits in the presence of phosphate as an allosteric inhibitor. Gel filtration experiments showed that TMGS is a hexameric enzyme, and its quaternary structure did not change in the presence of phosphate.

Microbial production and applications of 1,2-propanediol

1,2-Propanediol (propylene glycol) is an existing commodity chemical and can be produced from renewable resources using microbes. By virtue of being a natural product, relevant biochemical pathways can be harnessed into fermentation processes to produce 1,2-propanediol. In the present review, the chemical process and different biological strategies for the production of 1,2-propanediol are reviewed and compared with the potentials and limitations of all processes. For the successful commercial production of this diol, it is necessary to establish the metabolic pathways and production hosts (microorganisms), which are capable of delivering final product with high yields and volumetric productivity. Three pathways which have been recognized for 1,2-propanediol production are discussed here. In the first, de-oxy sugars like fucose and rhamnose are used as the carbon sources, while in the other route, the glycolytic intermediate-dihydroxyacetonephosphate (DHAP) is used to produce 1,2-propanediol via the formation of methylglyoxal. A new pathway of 1,2-propanediol production by lactic acid degradation under anoxic conditions and the enzymes involved is also discussed. The production of this diol has gained attention because of their newer applications in industries such as polymers, food, pharmaceuticals, textiles, etc. Furthermore, improvement in fermentation technology will permit its uses in other applications. Future prospect in the light of the current research and its potential as a major bulk chemical are discussed.

Methylglyoxal and glucose metabolism: a historical perspective and future avenues for research

Methylglyoxal, an alpha-oxoaldehyde discovered in the 1880s, has had a hectic scientific career, at times being considered of fundamental importance and at other times viewed as playing a very subordinate role. Much has been learned about methylglyoxal, but the function of its production in the metabolic machinery is still unknown. This paper gives an overview of the changing role of methylglyoxal from a historical aspect and arrives at the conclusion that methylglyoxal is tightly bound to glycolysis from an evolutionary perspective, its production therefore being inevitable. It is not situated in the main stream of the glycolytic sequence, but a role can be assigned to its production in the phosphate supply of operating glycolysis in some prokaryotes and yeast under conditions of phosphate deficiency. This function is presumed to be performed by the enzyme methylglyoxal synthase, which is specialized for the conversion of dihydroxyacetone-phosphate to methylglyoxal. However, it is still unknown whether this enzyme and this kind of regulation also exist in animals.

Rhamnose catabolism in Bacteroides thetaiotaomicron is controlled by the positive transcriptional regulator RhaR

Bacteroides thetaiotaomicron is an important human gut commensal, which also causes opportunistic infections outside this environment. It utilises a range of host and diet-related carbohydrates, including rhamnose. In this study, the rha gene cluster, required for rhamnose utilisation, was characterised by transcription analysis, gene targeted mutagenesis and enzyme assays. Growth in the presence of L-rhamnose induced transcription of all the genes of this cluster. The first five genes of the cluster, rhaKIPAO, were transcribed as an operon from a transcriptional start site upstream of rhaK, whereas the sixth gene, rhaR, was transcribed independently. Bioinformatic analysis and mutation of the rhaR gene identified it as encoding the positive transcriptional activator of rhaKIPAO. A rhaR mutant could not utilise rhamnose as the sole carbon source but grew normally on glucose. The rhaO gene encoded a lactaldehyde reductase, and a rhaO mutant produced reduced levels of L-1,2-propanediol during growth in rhamnose, indicating its contribution to rhamnose catabolism in Bacteroides thetaiotaomicron.

Clostridium beijerinckii and Clostridium difficile detoxify methylglyoxal by a novel mechanism involving glycerol dehydrogenase

In contrast to gram-negative bacteria, little is known about the mechanisms by which gram-positive bacteria degrade the toxic metabolic intermediate methylglyoxal (MG). Clostridium beijerinckii BR54, a Tn1545 insertion mutant of the NCIMB 8052 strain, formed cultures that contained significantly more (free) MG than wild-type cultures. Moreover, BR54 was more sensitive to growth inhibition by added MG than the wild type, suggesting that it has a reduced ability to degrade MG. The single copy of Tn1545 in this strain lies just downstream from gldA, encoding glycerol dehydrogenase. As a result of antisense RNA production, cell extracts of BR54 possess significantly less glycerol dehydrogenase activity than wild-type cell extracts (H. Liyanage, M. Young, and E. R. Kashket, J. Mol. Microbiol. Biotechnol. 2:87-93, 2000). Inactivation of gldA in both C. beijerinckii and Clostridium difficile gave rise to pinpoint colonies that could not be subcultured, indicating that glycerol dehydrogenase performs an essential function in both organisms. We propose that this role is detoxification of MG. To our knowledge, this is the first report of targeted gene disruption in the C. difficile chromosome.

Overexpression, purification, and characterization of the thermostable mevalonate kinase from Methanococcus jannaschii

We report here the first overexpression and characterization of a thermostable mevalonate kinase from an archae, Methanococcus jannaschii, a strict anaerobe, which produces methane and grows at pressure of 200 atm and an optimum temperature near 85 degrees C. PCR-derived DNA fragments containing the structural gene for mevalonate kinase were cloned into an expression vector, pET28a, to form pETMVK. The mevalonate kinase was overexpressed from Escherichia coli pETMVK/BL21(DE3) (15-20% of total soluble protein) when induced with isopropyl beta-d-thiogalactopyranoside. The protein was purified by heat treatment (to denature E. coli proteins), followed by metal-affinity chromatography on Talon metal-affinity resin column. The purified protein had a dimeric structure composed of identical subunits, and the M(r) of the enzyme determined by gel chromatography was 68K. Based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the subunit M(r) was 36, 000. The pI for mevalonate kinase was 7.8. The Michaelis constant (K(m)) for (RS)-mevalonate was 68.5 microM and was 92 microM for ATP. The V(max) was 387 units mg(-1). The optimal temperature for mevalonate kinase activity was 70-75 degrees C.