Degradation of glyoxylate and glycolate with ATP synthesis by a thermophilic anaerobic bacterium, Moorella sp. strain HUC22-1

Molecular Characteristics of the Malate Dehydrogenase (MDH) Gene Family in Spirometra mansoni (Cestoda: Diphyllobothriidea)

The plerocercoid larva of Spirometra mansoni can cause a parasitic zoonosis-sparganosis. Malate dehydrogenase (MDH) plays a very important role in the life activities of parasites. However, little is known about the MDH family in S. mansoni. We identified eight new MDH members in S. mansoni in this study. Clustering analysis divided SmMDHs into two groups and revealed patterns similar to the conserved motif organization. RT-qPCR suggested that five MDHs were highly expressed in the mature proglottid and that three MDHs were highly expressed in the gravid proglottid. Phylogenetic analysis revealed that SmMDHs contain both conserved family members and members in the process of further diversification. rSmMDH has an NAD binding domain, a dimer interface and a substrate binding domain. Natural SmMDH was immunolocalized in the tissues and follicles around the uterus in the mature or gravid proglottid and eggshells. The maximum forward and reverse reaction activities of rSmMDH were observed at pH 8.5 and 9.0, respectively. The optimum temperature for enzyme activity was 37 °C in the forward reaction and 40 °C in the reverse reaction. These results lay the foundation for studying the molecular functions and mechanisms of MDHs in S. mansoni and related taxa.

Bio-conversion of CO2 into biofuels and other value-added chemicals via metabolic engineering

Carbon dioxide (CO₂) occurs naturally in the atmosphere as a trace gas, which is produced naturally as well as by anthropogenic activities. CO₂ is a readily available source of carbon that in principle can be used as a raw material for the synthesis of valuable products. The autotrophic organisms are naturally equipped to convert CO₂ into biomass by obtaining energy from sunlight or inorganic electron donors. This autotrophic CO₂ fixation has been exploited in biotechnology, and microbial cell factories have been metabolically engineered to convert CO₂ into biofuels and other value-added bio-based chemicals. A variety of metabolic engineering efforts for CO₂ fixation ranging from basic copy, paste, and fine-tuning approaches to engineering and testing of novel synthetic CO₂ fixing pathways have been demonstrated. In this paper, we review the current advances and innovations in metabolic engineering for bio-conversion of CO₂ into bio biofuels and other value-added bio-based chemicals.

Anaerobic Microbial Metabolism of Dichloroacetate

Dichloroacetate (DCA) commonly occurs in the environment due to natural production and anthropogenic releases, but its fate under anoxic conditions is uncertain. Mixed culture RM comprising "Candidatus Dichloromethanomonas elyunquensis" strain RM utilizes DCA as an energy source, and the transient formation of formate, H2, and carbon monoxide (CO) was observed during growth. Only about half of the DCA was recovered as acetate, suggesting a fermentative catabolic route rather than a reductive dechlorination pathway. Sequencing of 16S rRNA gene amplicons and 16S rRNA gene-targeted quantitative real-time PCR (qPCR) implicated "Candidatus Dichloromethanomonas elyunquensis" strain RM in DCA degradation. An (S)-2-haloacid dehalogenase (HAD) encoded on the genome of strain RM was heterologously expressed, and the purified HAD demonstrated the cofactor-independent stoichiometric conversion of DCA to glyoxylate at a rate of 90 ± 4.6 nkat mg-1 protein. Differential protein expression analysis identified enzymes catalyzing the conversion of DCA to acetyl coenzyme A (acetyl-CoA) via glyoxylate as well as enzymes of the Wood-Ljungdahl pathway. Glyoxylate carboligase, which catalyzes the condensation of two molecules of glyoxylate to form tartronate semialdehyde, was highly abundant in DCA-grown cells. The physiological, biochemical, and proteogenomic data demonstrate the involvement of an HAD and the Wood-Ljungdahl pathway in the anaerobic fermentation of DCA, which has implications for DCA turnover in natural and engineered environments, as well as the metabolism of the cancer drug DCA by gut microbiota.IMPORTANCE Dichloroacetate (DCA) is ubiquitous in the environment due to natural formation via biological and abiotic chlorination processes and the turnover of chlorinated organic materials (e.g., humic substances). Additional sources include DCA usage as a chemical feedstock and cancer drug and its unintentional formation during drinking water disinfection by chlorination. Despite the ubiquitous presence of DCA, its fate under anoxic conditions has remained obscure. We discovered an anaerobic bacterium capable of metabolizing DCA, identified the enzyme responsible for DCA dehalogenation, and elucidated a novel DCA fermentation pathway. The findings have implications for the turnover of DCA and the carbon and electron flow in electron acceptor-depleted environments and the human gastrointestinal tract.

Genome-scale metabolic modeling of P. thermoglucosidasius NCIMB 11955 reveals metabolic bottlenecks in anaerobic metabolism

Parageobacillus thermoglucosidasius represents a thermophilic, facultative anaerobic bacterial chassis, with several desirable traits for metabolic engineering and industrial production. To further optimize strain productivity, a systems level understanding of its metabolism is needed, which can be facilitated by a genome-scale metabolic model. Here, we present p-thermo, the most complete, curated and validated genome-scale model (to date) of Parageobacillus thermoglucosidasius NCIMB 11955. It spans a total of 890 metabolites, 1175 reactions and 917 metabolic genes, forming an extensive knowledge base for P. thermoglucosidasius NCIMB 11955 metabolism. The model accurately predicts aerobic utilization of 22 carbon sources, and the predictive quality of internal fluxes was validated with previously published ¹³C-fluxomics data. In an application case, p-thermo was used to facilitate more in-depth analysis of reported metabolic engineering efforts, giving additional insight into fermentative metabolism. Finally, p-thermo was used to resolve a previously uncharacterised bottleneck in anaerobic metabolism, by identifying the minimal required supplemented nutrients (thiamin, biotin and iron(III)) needed to sustain anaerobic growth. This highlights the usefulness of p-thermo for guiding the generation of experimental hypotheses and for facilitating data-driven metabolic engineering, expanding the use of P. thermoglucosidasius as a high yield production platform.

Identification and characterization of cytosolic malate dehydrogenase from the liver fluke Fasciola gigantica

The liver fluke zoonoses, Fasciola spp. are parasitic helminths infecting humans and animals globally. Recent sequencing of the genome of Fasciola gigantica has provided a basis to understand the biochemistry of this parasite. Here, we identified the cytosolic malate dehydrogenase in F. gigantica (FgMDH) and characterized the enzyme biochemically and structurally. F. gigantica encodes a single cytosolic MDH, a key enzyme of the citric acid cycle. It catalyzes the reversible oxidation of malate to oxaloacetate using NAD⁺. The Fgmdh gene was amplified and cloned for expression of the recombinant protein. The purified protein showed a molecular weight of ~ 36 kDa that existed in a dimeric form in solution. The recombinant enzyme was catalytically active as it catalyzed both forward and reverse reactions efficiently. The kinetic parameters were determined for both directions. The structure of FgMDH and human MDH were modeled and validated. The superimposition of both the model structures showed overall structural similarity in the active site loop region, however, the conformation of the residues was different. Molecular docking elucidated the binding sites and affinities of the substrates and cofactors to the enzyme. Simulation of molecular dynamics and principal component analysis indicated the stability of the systems and collective motions, respectively. Understanding the structural and functional properties of MDH is important to better understand the roles of this enzyme in the biochemistry of the parasite.

Long-Term Biogas Production from Glycolate by Diverse and Highly Dynamic Communities

Generating chemical energy carriers and bulk chemicals from solar energy by microbial metabolic capacities is a promising technology. In this long-term study of over 500 days, methane was produced by a microbial community that was fed by the mono-substrate glycolate, which was derived from engineered algae. The microbial community structure was measured on the single cell level using flow cytometry. Abiotic and operational reactor parameters were analyzed in parallel. The R-based tool flowCyBar facilitated visualization of community dynamics and indicated sub-communities involved in glycolate fermentation and methanogenesis. Cell sorting and amplicon sequencing of 16S rRNA and mcrA genes were used to identify the key organisms involved in the anaerobic conversion process. The microbial community allowed a constant fermentation, although it was sensitive to high glycolate concentrations in the feed. A linear correlation between glycolate loading rate and biogas amount was observed (R² = 0.99) for glycolate loading rates up to 1.81 g L⁻¹ day⁻¹ with a maximum in biogas amount of 3635 mL day⁻¹ encompassing 45% methane. The cytometric diversity remained high during the whole cultivation period. The dominating bacterial genera were Syntrophobotulus, Clostridia genus B55_F, Aminobacterium, and Petrimonas. Methanogenesis was almost exclusively performed by the hydrogenotrophic genus Methanobacterium.

Cloning, sequencing and functional expression of cytosolic malate dehydrogenase from Taenia solium: Purification and characterization of the recombinant enzyme

We report herein the complete coding sequence of a Taenia solium cytosolic malate dehydrogenase (TscMDH). The cDNA fragment, identified from the T. solium genome project database, encodes a protein of 332 amino acid residues with an estimated molecular weight of 36517Da. For recombinant expression, the full length coding sequence was cloned into pET23a. After successful expression and enzyme purification, isoelectrofocusing gel electrophoresis allowed to confirm the calculated pI value at 8.1, as deduced from the amino acid sequence. The recombinant protein (r-TscMDH) showed MDH activity of 409U/mg in the reduction of oxaloacetate, with neither lactate dehydrogenase activity nor NADPH selectivity. Optimum pH for enzyme activity was 7.6 for oxaloacetate reduction and 9.6 for malate oxidation. K(cat) values for oxaloacetate, malate, NAD, and NADH were 665, 47, 385, and 962s(-1), respectively. Additionally, a partial characterization of TsMDH gene structure after analysis of a 1.56Kb genomic contig assembly is also reported.