Project description:Clostridium ljungdahlii can utilize CO as energy source during autotrophic growth. C. ljungdahlii grows sufficiently in CO and produces ethanol as the main product. In this study, C. ljungdahlii wild type and mutant were fermented on CO. C. ljungdahlii produced more ethanol than the ΔadhE1 mutant. The results showed that aldehyde dehydrogenase inactivation led to inefficient metabolism in C. ljungdahlii. Thus, comparative transcriptomes among cells grown on CO of WT and ΔadhE1 mutant were performed to investigate gene expression profiles based on three biological replicates.
Project description:Clostridium ljungdahlii not only utilizes CO, but also H2 as energy source during autotrophic growth. And C. ljungdahlii also grows in fructose fermentation. In theory, fructose is a more energetically favourable energy source than syngas in the fermentation of C. ljungdahlii. However, C. ljungdahlii grows insufficiently in fructose and produces less acetate and ethanol, compared to syngas fermentation. In this study, C. ljungdahlii wild type and mutants were fermented on fructose. C. ljungdahlii produced less ethanol than the ΔadhE1 mutant and consumed less fructose. The ΔadhE1+2 mutant cannot grow in the syngas fermentation and produced less ethanol among the three strains. The results showed that aldehyde dehydrogenase inactivation led to efficient metabolism in C. ljungdahlii and the bifunctional aldehyde/alcohol dehydrogenases inactivation led to decrease metabolism. Thus, comparative transcriptomes among cells grown on fructose of three strains were performed to investigate gene expression profiles based on three biological replicates.
Project description:Clostridium ljungdahlii not only utilizes CO, but also H2 as energy source during autotrophic growth. In theory, CO is a more energetically and thermodynamically favourable energy source than H2 in the gas fermentation of C. ljungdahlii. However, how C. ljungdahlii conserves energy for growth and ethanol/acetate formation grown on CO or CO2/H2 is not in great detail. In this study, C. ljungdahlii was fermented on CO and CO2/ H2 at pH 6.0 with 0.1 MPa gas pressure. C. ljungdahlii produced 27 g/L acetate, 9 g/L ethanol, 8 g/L 2,3-butanediol and traces of lactate in the presence of CO as energy source, while it produced 25.8 0.1 g/L acetate, 1.8 0.1 g/L ethanol, 0.7 0.01g/L 2,3-butanediol and trances of lactate in the same fermentation condition using H2 as energy source. Therefore, comparative transcriptomes between cells grown on CO and cells grown on H2/CO2 were performed to investigate gene expression profiles based on three biological replicates.
Project description:Transcriptomic profiles of the acetogen Clostridium ljungdahlii during lithoautotrophic growth with syngas or with H2 and CO2 compared to organoheterotrophic growth with fructose
Project description:The unique capability of acetogens to ferment a broad range of substrates renders them ideal candidates for the biotechnological production of commodity chemicals. In particular the ability to grow with H2:CO2 or syngas (a mixture of H2/CO/CO2) makes these microorganisms ideal chassis for sustainable bioproduction. However, advanced design strategies for acetogens are currently hampered by incomplete knowledge about their physiology and our inability to accurately predict phenotypes. Here we describe the reconstruction of a novel genome-scale model of metabolism and macromolecular synthesis (ME-model) to gain new insights into the biology of the model acetogen Clostridium ljungdahlii. The model represents the first ME-model of a Gram-positive bacterium and captures all major central metabolic, amino acid, nucleotide, lipid, major cofactors, and vitamin synthesis pathways as well as pathways to synthesis RNA and protein molecules necessary to catalyze these reactions, thus significantly broadens the scope and predictability. Use of the model revealed how protein allocation and media composition influence metabolic pathways and energy conservation in acetogens and accurately predicted secretion of multiple fermentation products. Predicting overflow metabolism is of particular interest since it enables new design strategies, e.g. the formation of glycerol, a novel product for C. ljungdahlii, thus broadening the metabolic capability for this model microbe. Furthermore, prediction and experimental validation of changing secretion rates based on different metal availability opens the window into fermentation optimization and provides new knowledge about the proteome utilization and carbon flux in acetogens.
Project description:Clostridium ljungdahlii derives energy by acetogenesis as a lithotrophic pathway and as part of various organotrophic pathways. Its recently sequenced genome has made it possible to discover changes in gene expression that occur in different growth modes, from which strategies for biofuel production may be developed. C. ljungdahlii was grown with fructose as an organoheterotrophic substrate and also lithoautotrophically, either on syngas or with H2 as the electron donor and CO2 as the electron acceptor. RNA extracted from all three conditions was analyzed by hybridization to a microarray, and gene expression was compared quantitatively by RNA-Seq of C. ljungdahlii grown with fructose and with H2 and CO2. Results. Strongly upregulated (> 10-fold, p < 0.05) genes with both syngas and H2/CO2 encode enzymes that degrade aspartate and arginine through the urea cycle to control the release of ammonia from amino acids. Numerous genes for uptake and degradation of peptides and amino acids, response to sulfur starvation, and molybdopterin-dependent pathways were also significantly (> 2-fold, p < 0.05) upregulated, along with three potentially NADPH-producing pathways for which the key metabolites are (S)-malate, ornithine and 6-phospho-D-gluconate. Upregulation of genes implicated in quorum sensing, sporulation and cell wall remodeling suggests a global and multicellular response to lithoautotrophic conditions. With syngas, (R)-lactate dehydrogenase and associated electron transfer flavoproteins were upregulated, representing a route of electron transfer from ferredoxin to NAD that is independent of the proton-translocating Rnf complex. With H2/CO2, a flavodoxin and histidine biosynthesis enzymes were upregulated. Genes for degradation of purine bases entering the cell by facilitated diffusion were upregulated in lithotrophic cells, whereas genes for degradation of adenine or adenosine derivatives entering by active transport were significantly (2-fold, p < 0.05) downregulated. The most downregulated genes, after those specific to fructose metabolism, encode enzymes of pyrimidine and purine biosynthesis, arginine fermentation to ornithine, threonine biosynthesis and phosphate uptake. Genes for biogenesis of an intracytoplasmic microcompartment were downregulated, within which (S)-1,2-propanediol dehydratase and other enzymes may dispose of methylglyoxal, a toxic byproduct of glycolysis, as 1-propanol. Several redox-active proteins, both cytoplasmic and membrane-associated, and predicted cell surface proteins were identified as differentially regulated. Conclusion. The transcriptomic profiles of C. ljungdahlii in lithoautotrophic and organoheterotrophic growth modes indicate large-scale physiological and metabolic differences, observations that may guide the production of biofuels and commodity chemicals with this species.