Clostridium thermocellum DSM 1313 Transcriptional Responses to Redox Perturbation
ABSTRACT: Clostridium thermocellum is a promising CBP candidate organism capable of directly converting lignocellulosic biomass to ethanol. Low yields, productivities and growth inhibition prevent industrial deployment of this organism for commodity fuel production. Symptoms of potential redox imbalance such as incomplete substrate utilization, and fermentation products characteristic of overflow metabolism, have been observed during growth. This perceived redox imbalance may be in part responsible for the mentioned bioproductivity limitations. Toward better understanding the redox metabolism of C. thermocellum, we analyzed gene expression, using microarrays, during addition of two stress chemicals (methyl viologen and hydrogen peroxide) which we observed to change fermentation redox potential. High quality RNA was extracted from C. thermocellum grown on cellobiose in chemostat culture and exposed, separately, to methyl viologen and hydrogen peroxide. Transcriptome profiles were obtained at seven time points during actively growing fermentations, 3 minutes, 15 minutes, 35 minutes, 7 hours, 14 hours, 50 hours, and 60 hours after beginning exposure to each stressor. Exposure treatments were carried out in duplicate and reference/untreated samples were taken before and between treatments, after flushing of stressor chemicals and re-equilibration of growth conditions.
Project description:Clostridium thermocellum is a Gram-positive, anaerobic, thermophilic bacterium that ferments cellulose into ethanol. It is a candidate industrial consolidated bioprocess (CBP) biocatalyst for lignocellulosic bioethanol production. However, C. thermocellum is relatively sensitive to ethanol compared to yeast. Previous studies have investigated the membrane and protein composition of wild-type and ethanol tolerant strains, but relatively little is known about the genome changes associated with the ethanol tolerant C. thermocellum strain. In this study, C. thermocellum cultures were grown to mid-exponential phase and then either shocked with the supplementation of ethanol to a final concentration of 3.95 g/L (equal to 0.5% [v/v]) or were untreated. Samples were taken pre-shock and 2, 12, 30, 60, 120, 240 min post-shock for multiple systems biology analyses. The addition of ethanol dramatically reduced the C. thermocellum growth and the final cell density was approximately half of the control fermentations, with concomitant reductions in substrate consumption in the treated cultures. The response of C. thermocellum to ethanol was dynamic and involved more than six hundred genes that were significantly and differentially expressed between the different conditions over time and every functional category was represented. Cellobiose was accumulated within the ethanol-shocked C. thermocellum cells, as well as the sugar phosphates such as fructose-6-P and cellobiose-6-P. The comparison and correlation among intracellular metabolites, proteomic and transcriptomics profiles as well as the ethanol effects on cellulosome, hydrogenase glycolysis and nitrogen metabolism are discussed, which led us to propose that C. thermocellum may utilize the nitrogen metabolism to bypass the arrested carbon metabolism in responding to ethanol stress shock, and the nitrogen metabolic pathway and redox balance may be the key target for improving ethanol tolerance and production in C. thermocellum. A thirty array study using total RNA recovered from wild-type cultures of Clostridium thermocellum at different time points of 0, 12, 30, 60, 120, and 240 min post-inoculation with 3.95 g/L [0.5% (v/v)] treatment compred to that of control without ethanol supplementation. Two biological replicates for treatment and control condition.
Project description:Clostridium thermocellum is a Gram-positive, anaerobic, thermophilic bacterium that ferments cellulose into ethanol. It is a candidate industrial consolidated bioprocess (CBP) biocatalyst for lignocellulosic bioethanol production to produce bioethanol directly from cellulosic biomass. However, few transcriptomic studies have been reported so far for C. thermocellum using biomass as carbon source. In this study, samples were taken from exponential and stationary phases of C. thermocellum cells growing in MTC media with pretreated switchgrass as carbon source, and transcriptomic profiling change of C. thermocellum during different growth phase was investigated using both expression array and tiling array. This study will help the understanding of gene expression of C. thermocellum using cellulosic biomass as carbon source and the knowledge will facilitate future metabolic engineering effort for strain improvement. [HX12 expression array]: A eleven array study using total RNA recovered from wild-type cultures of Clostridium thermocellum at different growth phase of T2 and T3 with switchgrass as carbon source. Two biological replicates used for each phase. [3Plex tiling array]: A six array study using total RNA recovered from wild-type cultures of Clostridium thermocellum at different growth phase of T2 and T3 with switchgrass as carbon source. Two biological replicates used for each phase.
Project description:The thermophilic anaerobe Clostridium thermocellum is a candidate consolidated bioprocessing (CBP) biocatalyst for cellulosic ethanol production. It expresses enzymes for both cellulose solubilization and its fermentation to produce lignocellulosic ethanol. To gain insights into the C. thermocellum genes, using an updated version of the C. thermocellum ATCC 27405 genome annotation, that are required for specific growth on the cellulosic feedstocks of either pretreated switchgrass or Populus, duplicate fermentations were conducted with a 5 g/L solid substrate loading. High quality RNA was extracted using a method we report for C. thermocellum grown on solid substrates. Transcriptome profiles were obtained at two time points during actively growing fermentations (12 h and 37 h post inoculation). A comparison of two transcriptomic analytical techniques, microarray and RNAseq, was performed and the data analyzed for statistical significance. When thresholds for genes passing significance of FDR>0.05 were applied, microarray (2351 genes) had a greater number of significant genes relative to RNA-seq (280 genes when normalized by KDMM). When a 2-fold difference in expression threshold was applied, seventy-three genes were significantly differentially expressed in common between the two techniques. We identified genes differentially expressed when C. thermocellum ATC 27405 was grown on the two biomass substrates, with two putative efflux/transport systems highly differentially regulated (>5-fold). This study has revealed consistency between these two transcriptomics analytical platforms that gives confidence in our switch from the DNA microarray platform to an RNAseq based platform for routine transcriptomics analyses. To gain insights into the C. thermocellum genes, using an updated version of the C. thermocellum ATCC 27405 genome annotation, that are required for specific growth on the cellulosic feedstocks of either pretreated switchgrass or Populus, duplicate fermentations were conducted with a 5 g/L solid substrate loading. High quality RNA was extracted using a method we report for C. thermocellum grown on solid substrates. Transcriptome profiles were obtained at two time points during actively growing fermentations (12 h and 37 h post inoculation). A comparison of two transcriptomic analytical techniques, microarray and RNAseq, was performed and the data analyzed for statistical significance.
Project description:Background: Clostridium thermocellum is a Gram-positive, anaerobic, thermophilic bacterium with a great potential to be a consolidated bioprocessing biocatalyst that can ferment cellulose to ethanol. To understand its physiology and genetic targets for future strain development, we have carried out several studies including ethanol-tolerant mutant resequencing and ethanol shock experiments. Methods: In this study, several approaches were applied to enrich mRNA for next-generation sequencing based RNA-Seq and the transcriptomic profiling of C. thermocellum ethanol shock responses was investigated using high-density tiling array and RNA-Seq. Correlations among different transcriptomic platforms of expression array, tiling array, and RNA-Seq were then compared, and data generated from systems biology studies were used for transcriptional architecture improvement. Results: Our results indicate that cloning-based Sanger sequencing can be used for mRNA enrichment ratio determination, and low-copy number plasmid performed better than high-copy one for cDNA library construction. In addition, high correlations were observed among same array platform using different analyses as well as those between two different array platforms of tiling and expression array when probe intensity was compared. Correlations between RNA-Seq and array results especially the one between RNA-Seq and tiling array are also high. Moreover, combining both RNA-Seq and microarray data the transcriptional architecture of C. thermocellum including the prediction and verification of novel transcript (gene), transcriptional start site (TSS), CAZyme genes, ncRNA, and operon were systematically updated and improved. Conclusions: RNA-seq has high correlation with array-based transcriptomic platforms and can provide additional information for transcriptional architecture and genome annotation improvement, which will facilitate future omics-based studies. A twelve array study using total RNA recovered from wild-type cultures of Clostridium thermocellum at different time points of 30, 60, and 120 min post-inoculation with 3.95 g/L [0.5% (v/v)] treatment compred to that of control without ethanol supplementation. Two biological replicates for treatment and control condition.
Project description:The thermophilic anaerobe Clostridium thermocellum is a candidate consolidated bioprocessing biocatalyst for the conversion of lignocellulosic biomass into ethanol. The microorganism expresses enzymes for both cellulose solubilization and fermentation to produce lignocellulosic ethanol making it a good candidate for industrial biofuel production. Intolerance to stresses routinely encountered during industrial fermentations may hinder the commercial development of this organism. A recently published study by Yang et al., (2012) characterized the physiological and regulatory response of C. thermocellum to ethanol supplementation. Significant changes in nitrogen metabolism and an accumulation of carbon sources were identified, revealing potential targets for metabolic engineering. In the current study, the response of C. thermocellum to heat and furfural shock were compared with the known effects of ethanol shock. Improved tolerance to these stresses are desirable traits for C. thermocellum and further understanding of the effects that these particular stresses have on the organism are the focus of this work. A forty one array study using total RNA recovered from wild-type cultures of Clostridium thermocellum at different time points of 10, 30, 60, and 120 min post-treatment with 3.95 g.L-1 ethanol, 4 g.L-1 furfural or 68°C treatment compred to that of control without treatment. At least two biological replicates were performed for each treatment and control condition.
Project description:Four C. thermocellum DSM-1313 derived strains were assessed using metabolite and DNA microarray tools in order to better understand carbon and electron flow within this organism. C. thermocellum is able to ferment cellulose into its fermentation end products L-lactate, acetate, formate, hydrogen gas, and ethanol, with the latter being the desired end product to be used as biorenewable fuel. In addition to the parent strain (genotype: hpt spo0A), strains with either or both of the genes encoding lactate dehydrogenase (ldh) and phosphate acetyltransferase (pta) deleted were studied. The strains used are a parent strain (M1726: genotype: hpt spo0A), and strains with either the gene encoding lactate dehydrogenase (M1629: hpt spo0A ldh) or phosphate acetyltransferase (M1630: hpt spo0A pta) deleted, or with both genes deleted (M1725: hpt spo0A ldh pta). Controlled batch fermentations using cellobiose as sole carbon source were grown for each strain, and samples in mid-exponential phase and at the time of carbon depletion were examined by DNA microarray. Four strains were grown each as three independent biological replicates (fresh batch of media was made before each run). Per fermentation, two samples were taken for DNA microarray analysis as was determined by the optical density: mid-exponential was defined as O.D. 0.4 (measured by Dasgip probe); point of carbon depletion was defined by both the maximum O.D. reached and observation that no base was added to the fermentation to control pH. In total, 4 strains x 3 fermentation x 2 time points per fermentor = 24 arrays. Parent strain was used as reference strain.
Project description:Staphylococcus aureus can survive in the low redox potential environment of the host cytosol. How low redox potential affects S. aureus USA300 Je2 was investigated by establishing aerobic steady state chemostat cultures and then perturbing the steady state by addition of the reducing agent dithiothreitol. These highly controlled steady state cultures allowed only one parameter (redox potential) changed. Dithiothreitol was used as a non-metabolizable reductant. Before and after perturbation samples were taken for gene expression profiling. Three independent biological replicates were analyzed.
Project description:The high cellulose digestion capability of the anaerobic thermophilic bacterium, Clostridium thermocellum, can be attributed to its efficient glycoside hydrolase system, consisting of both a free-enzyme system and a cellulosomal system, wherein carbohydrate active enzymes (CAZymes) are organized by primary and secondary scaffoldin proteins into large protein complexes bound to the bacterial cell wall. Using an integrated series of experiments encompassing polysaccharide depolymerization assays, direct biochemical analyses and transcriptomics, we show herein that, in addition to cell-bound cellulosomes and “free” enzymes, C. thermocellum naturally employs a system of cell-free cellulosomes that are not designed to be tethered to the cell and can diffuse away to attack polysaccharide substrates at some distance from the cell. By characterizing the cells and the secretomes of a series of mutants in which genes for either individual scaffoldins or combinations thereof are deleted, we demonstrate that the cellulosome is far more important in cellulose degradation than are the free enzymes, and that the primary scaffoldin CipA is much more important for the action of the cellulosomes than is the collective contribution of the secondary scaffoldins. Extensive transcriptomics analyses confirm the above results and extend the study to the effects of scaffoldin deletions on the organism as a whole. To gain insights into the transcriptome profiles of C. thermocellum strains when various cellulosomal scaffoldin genes were deleted. High quality RNA was extracted from C. thermocellum grown on cellulose. Transcriptome profiles were obtained at one time point during actively growing fermentations, mid exponential phase when 50% of the substrate had been consumed.
Project description:Clostridium thermocellum is a leading candidate organism for implementing a consolidated bioprocessing (CBP) strategy for biofuel production due to its native ability to rapidly consume cellulose and its existing ethanol production pathway. C. thermocellum converts cellulose and cellobiose to lactate, formate, acetate, H2, ethanol, amino acids, and other products. Elimination of the pathways leading to products such as H2 could redirect carbon flux towards ethanol production. Rather than delete each hydrogenase individually, we targeted a hydrogenase maturase gene (hydG), which is involved in converting the three [FeFe] hydrogenase apoenzymes into holoenzymes by assembling the active site. This functionally inactivated all three Fe-Fe hydrogenases simultaneously, as they were unable to make active enzymes. In the ∆hydG mutant, the [NiFe] hydrogenase-encoding ech was also deleted to obtain a mutant that functionally lacks all hydrogenase. The ethanol yield increased nearly 2-fold in ∆hydG∆ech compared to wild type, and H2 production was below the detection limit. Interestingly, ∆hydG and ∆hydG∆ech exhibited improved growth in the presence of acetate in the medium. Transcriptomic and proteomic analysis reveal that genes related to sulfate transport and metabolism were up-regulated in the presence of added acetate in ∆hydG, resulting in altered sulfur metabolism. Further genomic analysis of this strain revealed a mutation in the bi-functional alcohol/aldehyde dehydrogenase adhE gene, resulting in a strain with both NADH- and NADPH-dependent alcohol dehydrogenase activities, whereas the wild type strain can only utilize NADH. This is the exact same adhE mutation found in ethanol-tolerant C. thermocellum strain E50C, but ∆hydG∆ech is not more ethanol tolerant than the wild type. Targeting protein post-translational modification is a promising new approach to target multiple enzymes simultaneously for metabolic engineering. A seventeen array study using total RNA recovered from fermentation cultures of three strains (parental, ∆hydG and ∆hydG∆ech) of Clostridium thermocellum DSM1313. Cells were harvested at an OD 0.4-0.5 from cultures grown in the presence of additional 5mM acetate and compared to untreated controls. At least two biological replicates were performed for each treatment and control condition.
Project description:Artificial electron carriers have been widely used to shift the solvent ratio towards butanol in acetone-butanol-ethanol (ABE) fermentation of solventogenic clostridia according to decreased hydrogen production. In this study, first insights on the molecular level were gained to explore the effect of methyl viologen addition to cultures of Clostridium acetobutylicum. Employing batch fermentation in mineral salts medium, the butanol:acetone ratio was successively increased from 2.3 to 12.4 on a 100 ml scale in serum bottles and from 1.4 to 16.5 on a 1,300 ml scale in bioreactors, respectively. The latter cultures were used for DNA microarray analyses to provide new information on the transcriptional changes referring to methyl viologen exposure and thus, exhibing gene expression patterns according to the manipulation of the cellular redox balance.