Transcription profiling by array of Clostridium acetobutylicum on glucose and xylose substrates under exponential, continuous and diauxie growth.
ABSTRACT: Clostridium acetobutylicum was grown in a batch-culture with minimal medium containing glucose and xylose as substrate. Diauxie growth was observed after glucose was consumed. Following the organism grows on xylose. Transcriptional analysis was done to pursue the cellular processes during the switch from growth on glucose to growth on xylose. We compared DNA-Microarray data from cells grown during the exponential phase on glucose (A), with cells growing during the start of diauxie growth lag (B), during the end of diauxie growth lag (C) and during exponential growth on xylose (D). We used cells grown in a continuous culture with glucose as substrate as common reference for the samples A-D.
Project description:In order to identify genes which contribute on the uptake of glucose into cells of the mutant R. eutropha G+1, a genome wide transcription analyses was done. Transcripts of strain H16 and the glucose-utilizing mutant R. eutropha G+1, cultivated in mineral salts medium supplemented with either fructose or glucose were compared.
Project description:Oxidative stress is harmful for organism and occurs when the cells exposed to superoxid, hydrogen peroxide and alkylhydroperoxides. In microorganism, the glutathione- and thioredoxin-dependent reduction systems are universal and play an important role in response to defending oxidative stress. The _-glutamylcysteine synthetase (_-GCS) is an essential enzyme to biosynthesize the tripeptide glutathione (GSH) in organism. Similarly, thioredoxin reductase is an important enzyme in thioredoxin-dependent reduction system. In Clostridium acetobutylicum, the _-glutamylcysteine synthetase (encoded by CAC1539, gcs) and thioredoxin reductase (encoded by CAC1548, trxB) were inactivated using ClosTron technology. The gcs mutant grew insufficiently and consumed less glucose in the phosphate-limited continuous culture and exhibited more sensitive to oxidative stress. The trxB mutant just exhibited lower growth rate and less glucose uptake in the solventogenic phase, compared to wild type. The DNA microarrays were performed to investigate the transcripome difference between wild type and the mutants. In gcs mutant, the genes related to chemotaxis and flagella biosynthesis proteins were induced significantly and in the trxB mutant, the sporulation genes were induced largely. Based on the phenotypes and transcriptome comparison results, the relationship between GSH- and Trx-dependent induction systems was discussed in Clostridium acetobutylicum.
Project description:Alkaline hemicellulytic bacteria Bacillus sp. N16-5 has abroad substrate spectrum and exhibits great growth ability on complex carbohydrates. In order to get insight into its carbohydrate utilization mechanism, global transcriptional profiles were separately determined for growth on glucose, fructose, mannose, galactose, arabinose, xylose, galactomannan, xylan, pectin and carboxymethyl cellulose by using one-color microarrays. Substrate induced gene expression was measured when culture was grown on glucose, fructose, mannose, galactose, arabinose, xylose, galactomannan, xylan and CMC to mid-logarithmic phase.
Project description:Clostridium acetobutylicum is a Gram-positive, endospore-forming bacterium that is considered as a strict anaerobe. It ferments sugars to the organic acids acetate and butyrate or shifts to formation of the solvents - ethanol, butanol and acetone. In most bacteria the major regulator of iron homeostasis is Fur (ferric uptake regulator). Analysis of the genome of Clostridium acetobutylicum has revealed three genes encoding Fur-like proteins. The amino acid sequece of one of them showed 70% similarity to the Fur protein of the closely related Bacillus subtilis.<br>Thus, to gain insight into the role of Fur and the mechanisms for maintenance of iron homeostasis in this strict anaerobic organism, we determined its transcriptional profile in response to iron limitation and inactivation of fur.
Project description:BACKGROUND:The yeast Saccharomyces cerevisiae is unable to ferment pentose sugars like d-xylose. Through the introduction of the respective metabolic pathway, S. cerevisiae is able to ferment xylose but first utilizes d-glucose before the d-xylose can be transported and metabolized. Low affinity d-xylose uptake occurs through the endogenous hexose (Hxt) transporters. For a more robust sugar fermentation, co-consumption of d-glucose and d-xylose is desired as d-xylose fermentation is in particular prone to inhibition by compounds present in pretreated lignocellulosic feedstocks. RESULTS:Evolutionary engineering of a d-xylose-fermenting S. cerevisiae strain lacking the major transporter HXT1-7 and GAL2 genes yielded a derivative that shows improved growth on xylose because of the expression of a normally cryptic HXT11 gene. Hxt11 also supported improved growth on d-xylose by the wild-type strain. Further selection for glucose-insensitive growth on d-xylose employing a quadruple hexokinase deletion yielded mutations at N366 of Hxt11 that reversed the transporter specificity for d-glucose into d-xylose while maintaining high d-xylose transport rates. The Hxt11 mutant enabled the efficient co-fermentation of xylose and glucose at industrially relevant sugar concentrations when expressed in a strain lacking the HXT1-7 and GAL2 genes. CONCLUSIONS:Hxt11 is a cryptic sugar transporter of S. cerevisiae that previously has not been associated with effective d-xylose transport. Mutagenesis of Hxt11 yielded transporters that show a better affinity for d-xylose as compared to d-glucose while maintaining high transport rates. d-glucose and d-xylose co-consumption is due to a redistribution of the sugar transport flux while maintaining the total sugar conversion rate into ethanol. This method provides a single transporter solution for effective fermentation on lignocellulosic feedstocks.
Project description:We evolved Thermus thermophilus to efficiently co-utilize glucose and xylose, the two most abundant sugars in lignocellulosic biomass, at high temperatures without carbon catabolite repression. To generate the strain, T. thermophilus HB8 was first evolved on glucose to improve its growth characteristics, followed by evolution on xylose. The resulting strain, T. thermophilus LC113, was characterized in growth studies, by whole genome sequencing, and (13)C-metabolic flux analysis ((13)C-MFA) with [1,6-(13)C]glucose, [5-(13)C]xylose, and [1,6-(13)C]glucose+[5-(13)C]xylose as isotopic tracers. Compared to the starting strain, the evolved strain had an increased growth rate (~2-fold), increased biomass yield, increased tolerance to high temperatures up to 90°C, and gained the ability to grow on xylose in minimal medium. At the optimal growth temperature of 81°C, the maximum growth rate on glucose and xylose was 0.44 and 0.46h(-1), respectively. In medium containing glucose and xylose the strain efficiently co-utilized the two sugars. (13)C-MFA results provided insights into the metabolism of T. thermophilus LC113 that allows efficient co-utilization of glucose and xylose. Specifically, (13)C-MFA revealed that metabolic fluxes in the upper part of metabolism adjust flexibly to sugar availability, while fluxes in the lower part of metabolism remain relatively constant. Whole genome sequence analysis revealed two large structural changes that can help explain the physiology of the evolved strain: a duplication of a chromosome region that contains many sugar transporters, and a 5x multiplication of a region on the pVV8 plasmid that contains xylose isomerase and xylulokinase genes, the first two enzymes of xylose catabolism. Taken together, (13)C-MFA and genome sequence analysis provided complementary insights into the physiology of the evolved strain.
Project description:BACKGROUND: Engineering of Saccharomyces cerevisiae for the simultaneous utilization of hexose and pentose sugars is vital for cost-efficient cellulosic bioethanol production. This yeast lacks specific pentose transporters and depends on endogenous hexose transporters for low affinity pentose uptake. Consequently, engineered xylose-fermenting yeast strains first utilize D-glucose before D-xylose can be transported and metabolized. RESULTS: We have used an evolutionary engineering approach that depends on a quadruple hexokinase deletion xylose-fermenting S. cerevisiae strain to select for growth on D-xylose in the presence of high D-glucose concentrations. This resulted in D-glucose-tolerant growth of the yeast of D-xylose. This could be attributed to mutations at N367 in the endogenous chimeric Hxt36 transporter, causing a defect in D-glucose transport while still allowing specific uptake of D-xylose. The Hxt36-N367A variant transports D-xylose with a high rate and improved affinity, enabling the efficient co-consumption of D-glucose and D-xylose. CONCLUSIONS: Engineering of yeast endogenous hexose transporters provides an effective strategy to construct glucose-insensitive xylose transporters that are well integrated in the carbon metabolism regulatory network, and that can be used for efficient lignocellulosic bioethanol production.