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.

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: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: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:Background: Lignocellulosic biomass is a promising renewable feedstock for the microbial production of fuels. To release the major fermentable sugars such as glucose and xylose, pretreatment, hydrolysis, and subsequent conditioning of biomass feedstock are needed. During this process, many toxic compounds are produced or introduced which subsequently inhibit microbial growth and in many cases the production titer and rate. An understanding of the toxic effects of compounds found in hydrolysate on the fermentation microorganism is critical to improving biofuel yields in the process. One of the inhibitory compounds is furfural, liberated from hemicelluloses, which strongly inhibits the cell growth and ethanol production especially from xylose. Zymomonas mobilis is a capable ethanologenic bacterium with high ethanol productivity and high levels of ethanol tolerance. The development of robust biocatalyst to tolerate the lignocellulosic pretreatment inhibitors is one of the key elements for economic biofuel production. Results: In this study, the molecular responses of Z. mobilis to furfural, one major pretreatment inhibitor, were investigated using transcriptomic approaches of chip-based microarray. Furfural shock time course experiment with 3 g/L furfural supplemented when cells reach exponential phase and stress response experiment in the presence of 2 g/L furfural from the beginning of fermentation were carried out to study the short and long-term effect of furfural on 8b physiological and transcriptional profiles. The presence and supplementation of furfural negatively affect 8b growth in terms of final biomass and the fermentation time. Transcriptomic studies indicated that the response of 8b to furfural is dynamic, complex and differences exist between short-term shock response and long-term stress response. However, the gene function categories are similar with most downregulated genes related to translation and biosynthesis, while the furfural-upregulated genes were mostly related to cellular processes of general stress response and energy metabolism. Conclusions: Similar to previous report that acetate inhibited the growth of Z. mobilis 8b in RM using glucose or xylose as carbon source, the existence or supplementation of another major hydrolysate inhibitor furfural also inhibited 8b growth with slowing the substrate utilization and ethanol production. The difference between carbon sources is more dramatic than that of the major hydrolysate inhibitors of both NH4OAc (GSE57553) and furfural (this study). Several gene targets have been selected for genetic studies with promising preliminary results.

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Clostridium thermocellum Transcriptomic Profiles after Exposure to Furfural or Heat Stress

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