US20020081677A1 - Ethanol production - Google Patents

Ethanol production Download PDF

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US20020081677A1
US20020081677A1 US09/971,361 US97136101A US2002081677A1 US 20020081677 A1 US20020081677 A1 US 20020081677A1 US 97136101 A US97136101 A US 97136101A US 2002081677 A1 US2002081677 A1 US 2002081677A1
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gene
sequence
gram
positive bacterium
dna sequence
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Muhammad Javed
Fiona Cusdin
Paul Milner
Edward Green
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Elsworth Biotechnology Ltd
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Elsworth Biotechnology Ltd
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Assigned to ELSWORTH BIOTECHNOLOGY LIMITED reassignment ELSWORTH BIOTECHNOLOGY LIMITED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CUSDIN, FIONA, GREEN, EDWARD, JAVED, MUHAMMAD, MILNER, PAUL
Publication of US20020081677A1 publication Critical patent/US20020081677A1/en
Priority to US11/108,870 priority patent/US20050181492A1/en
Priority to US12/391,366 priority patent/US8097460B2/en
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    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/0004—Oxidoreductases (1.)
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
    • C12P7/00—Preparation of oxygen-containing organic compounds
    • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
    • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
    • C12P7/06—Ethanol, i.e. non-beverage
    • C12P7/065—Ethanol, i.e. non-beverage with microorganisms other than yeasts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E50/00—Technologies for the production of fuel of non-fossil origin
    • Y02E50/10—Biofuels, e.g. bio-diesel

Definitions

  • This invention relates to the production of ethanol as a product of bacterial fermentation.
  • this invention relates to a novel method of gene inactivation and gene expression based upon homologous recombination.
  • Glycolysis is the series of enzymatic steps whereby the six carbon glucose molecule is broken down, via multiple intermediates, into two molecules of the three carbon compound pyruvate.
  • the glycolytic pathways of many bacteria produce pyruvate as a common intermediate.
  • Subsequent metabolism of pyruvate results in a net production of NADH and ATP as well as waste products commonly known as fermentation products.
  • ATP is generated via glycolysis. Additional ATP can also be regenerated during the production of organic acids such as acetate. NAD + is regenerated from NADH during the reduction of organic substrates such as pyruvate or acetyl CoA. Therefore, the fermentation products of glycolysis and pyruvate metabolism include organic acids, such as lactate, formate and acetate as well as neutral products such as ethanol.
  • the main energy pathway for the metabolism of pyruvate is via the pyruvate-formate-lyase (PFL) pathway to give formate and acetyl-CoA.
  • Acetyl-CoA is then converted to acetate, via phosphotransacetylase (PTA) and acetate kinase (AK) with the co-production of ATP, or reduced to ethanol via acetaldehyde dehydrogenase (AcDH) and alcohol dehydrogenase (ADH).
  • NADH In order to maintain a balance of reducing equivalents, excess NADH produced from glycolysis is re-oxidised to NAD + by lactate dehydrogenase (LDH) during the reduction of pyruvate to lactate.
  • LDH lactate dehydrogenase
  • NADH can also be re-oxidised by AcDH and ADH during the reduction of acetyl-CoA to ethanol but this is a minor reaction in cells with a functional LDH. Theoretical yields of ethanol are therefore not achieved since most acetyl CoA is converted to acetate to regenerate ATP and excess NADH produced during glycolysis is oxidised by LDH.
  • Ethanologenic microorganisms such as Zymomonas mobilis and yeast
  • Ethanologenic microorganisms are capable of a second type of anaerobic fermentation commonly referred to as alcoholic fermentation in which pyruvate is metabolised to acetaldehyde and CO 2 by pyruvate decarboxylase (PDC).
  • PDC pyruvate decarboxylase
  • Acetaldehyde is then reduced to ethanol by ADH regenerating NAD + .
  • Alcoholic fermentation results in the metabolism of 1 molecule of glucose to two molecules of ethanol and two molecules of CO 2 .
  • DNA which encodes both of these enzymes in Z. mobilis has been isolated, cloned and expressed recombinantly in hosts capable of producing high yields of ethanol via the synthetic route described above.
  • mobilis can both be integrated via the use of a pet operon to produce Gram negative recombinant hosts, including Erwina, Klebsiella and Xanthomonas species, each of which expresses the heterologous genes of Z. mobilis resulting in high yield production of ethanol via a synthetic pathway from pyruvate to ethanol.
  • U.S. Pat. No. 5,482,846 discloses the simultaneous transformation of mesophilic Gram positive Bacillus sp with heterologous genes which encode both the PDC and ADH enzymes so that the transformed bacteria produce ethanol as a primary fermentation product. There is no suggestion that bacteria transformed with the pdc gene alone will produce ethanol.
  • EP-A-0761815 describes a method of homologous recombination whereby a sporulation gene is inserted into Bacillus thurengiensis.
  • EP-A-0603416 describes a method of homologous recombination whereby an arbitary gene is inserted into Lactobacillus delbrueckii.
  • EP-A-0415297 describes a method of producing Bacillus strains expressing a mutant protease.
  • Biwas et al. (J. Bacteriol., 175, 3628-3635, 1993) describes a method of homologous recombination whereby Lactococcus lactis has a chromosomal gene replaced by a plasmid carried modified copy.
  • the method uses a thermosensitive plasmid and cannot be used to transform a thermophilic bacterium.
  • thermophilic microorganisms that operate at high temperature.
  • the conversion rate of carbohydrates into ethanol is much faster.
  • ethanol productivity in a thermophilic Bacillus is up to ten-fold faster than a conventional yeast fermentation process which operates at 30° C. Consequently, a smaller production plant is required for a given volumetric productivity, thereby reducing plant construction costs.
  • At high temperature there is a reduced risk of contamination in the fermenter from other microorganisms, resulting in less downtime, increased plant productivity and a lower energy requirement for feedstock sterilisation.
  • fermentation cooling is not required, reducing operating costs further.
  • the heat of fermentation helps to evaporate ethanol, which reduces the likelihood of growth inhibition from high ethanol concentrations, a common problem with most bacterial fermentations. Ethanol evaporation in the fermenter head space also facilitates product recovery.
  • the inventors' strain originates from a wild-type isolate that is a natural composting organism and far more suited for the conversion of sugars found in agricultural feedstocks to ethanol than traditional mesophilic microorganisms.
  • the base strain possesses all the genetic machinery for the conversion of hexose and pentose sugars, and cellobiose to ethanol; the inventors have simply blocked the LDH pathway to increase ethanol yields. This process is called self-cloning and does not involve expression of foreign DNA. Consequently, the resulting organism does not fall under the safety regulations imposed on the use of genetically modified organisms (GMOs).
  • the inventors initiated a molecular biology program to tackle the stability problem and gain a better insight into the genetic systems involved in ethanol formation.
  • the inventors first developed genetic techniques to specifically manipulate the organism and a sporulation deficient mutant amenable to genetic manipulation was then selected in continuous culture.
  • the inventors then sequenced several key metabolic genes; lactate dehydrogenase (ldh), lactase permease (lp), alcohol dehydrogenase (adh) and a novel insertion sequence located within the ldh gene.
  • DNA sequence analysis of the ldh gene from the chemically mutated strain revealed that the gene had been inactivated by the insertion of a naturally occurring insertion sequence element (IE) (also referred to as an IS element) in the coding region of the gene. Transposition into (and out of) the ldh gene and subsequent gene inactivation is itself unstable, resulting in reversion.
  • IE insertion sequence element
  • the inventors determined that the IE sequence within the ldh gene provides a large area for homologous recombination. It was therefore proposed that the stability of the ldh mutation could be improved by integration of plasmid DNA into the IE sequence already present within the ldh gene of strain TN.
  • Strain improvement has been achieved through a novel method of gene integration based on homologous recombination.
  • the site of integration and plasmid for recombination can also be used to integrate and overexpress native or heterologous genes.
  • the IE sequence was amplified from TN chromosomal DNA by PCR. Primers were chosen from the ldh gene sequence that flanked the insertion sequence and a HindIII restriction site was introduced into the upstream primer and a XbaI restriction site was introduced into the downstream primer to create convenient restriction sites for subsequent cloning into plasmid pUBUC. A 3.2 kb PCR fragment containing the insertion sequence was trimmed using HindIII and XbaI restriction endonucleases and subsequently cloned into plasmid pUBUC resulting in plasmid pUBUC-IE (FIG. 5).
  • strain TN-T9 was grown under pH controlled conditions in continuous culture without kanamycin selection to check for strain stability. Stability of strain TN-T9 was confirmed using sub-optimal fermentation conditions such that residual sugar was present within the fermentation medium; conditions which favour reversion. The fermentation ran continuously for 750 hours without any trace of lactate production despite the presence of residual sugar within the fermentation medium, pyruvate excretion and numerous deviations from the set conditions. Ethanol was produced in relatively large amounts throughout the fermentation FIG. 4, indicating that the ldh gene mutation in strain TN-T9 is stable in continuous culture under the experimental conditions provided.
  • the inventors have also optimised the fermentation conditions for cell growth and ethanol production for Bacillus strain TN-T9.
  • the inventors have developed a dual system for improving the stability of the ldh mutant whilst expressing pdc and adh genes optionally using a pdc/adh operon.
  • the inventors have also isolated and sequenced a novel ldh gene and insertion sequence element, as well as novel lactate permease and alcohol dehydrogenase genes.
  • the inventors have developed a technique for the integration of plasmid DNA into the chromosome and selection of recombinant Bacillus sp and have developed a set of optimised conditions for the production of ethanol by bacterial fermentation.
  • a first aspect of the present invention relates to a recombinant thermophilic, Gram-positive bacterium which has been transformed using a method of homologous recombination for stabilising a gene mutation and for inserting an expressible gene.
  • the invention also provides a recombinant thermophilic, Gram-positive bacterium in which the stability of the ldh mutation has been enhanced by homologous recombination between a plasmid and the chromosomal DNA of the bacterium resulting in a strain for the production of ethanol as a product of bacterial fermentation.
  • the Gram-positive bacterium is a strain of B. thermoglucosidasius.
  • the Gram-positive bacterium has been transformed with a plasmid harbouring an IE sequence as set forth in FIG. 1, or a functional portion or variant thereof.
  • the IE sequence of FIG. 1, or functional variant or portion thereof is stably incorporated into the chromosome of the recombinant bacterium by homologous recombination.
  • integration of the IE sequence into the chromosome of the recombinant bacterium will result in the inactivation of the native ldh gene.
  • the Gram-positive bacterium is Bacillus strain TN-T9 (NCIMB Accession no. NCIMB 41075 deposited on Sep. 8, 2000 in accordance with the terms of the Budapest Treaty).
  • the Gram-positive bacterium is Bacillus strain TN-TK (NCIMB Accession no. NCIMB 41115 deposited on Sep. 27, 2001 in accordance with the terms of the Budapest Treaty).
  • the present invention also relates to a Gram-positive bacterium obtained by selecting mutants of TN-T9 which are kanamycin sensitive. A suitable method for obtaining such strains is described in the appended examples.
  • the Gram-positive bacterium is sporulation deficient.
  • a Gram-positive bacterium wherein a native ldh gene has been inactivated by homologous recombination and one or more expressible genes have been inserted into the chromosomal DNA of the bacterium. Furthermore, gene expression may be increased by increased gene copy number following multiple insertions of the plasmid into the insertion sequence either as a result of one round or repeated rounds of integration.
  • the one or more expressible genes may be inserted into one or more IE sequences present in the chromosomal DNA of the bacterium.
  • IE sequences present in the chromosomal DNA of the bacterium there are 3 IE sequences on the chromosome of strains TN-T9 and TN-TK.
  • the gene to be expressed may be native to Bacillus such as alcohol dehydrogenase or foreign (i.e. heterlogous such as pyruvate decarboxylase from Z. mobilis and ⁇ -amylase from B. stearothermophilus.
  • the genes may also be arranged in an operon under the same transcriptional control. Gene expression may be regulated by manipulating the copy number of the gene and by using different transcriptional promoter sequences.
  • the one or more genes are pdc and/or adh.
  • a third aspect of the invention there is provided a method of inactivating a native ldh gene and inserting one or more expressible genes into the chromosome of a bacterium by homologous recombination.
  • the bacterium is a thermophilic Gram-positive bacterium.
  • the gene to be inactivated is a native ldh gene and the one or more expressible genes are a pdc gene and a adh gene.
  • the pdc gene and the adh gene form part of a PDC operon operatively linked to the IE sequence of FIG. 1 on the same plasmid.
  • the pdc gene is heterologous to the cell.
  • both the IE sequence of FIG. 1 and the PDC operon, or portions thereof, are stably integrated into the chromosome of the bacterium.
  • the method of gene inactivation and expression comprises the use of a shuttle vector, as set forth in FIG. 5, which is able to replicate in E. coli and Bacillus strains at temperatures up to 54° C.
  • a shuttle vector which is able to replicate in both E. coli and Bacillus sp at temperatures up to 54° C., which confers resistance to ampicillin and kanamycin and which harbours the IE sequence, or a portion thereof as set forth in FIG. 1, from Bacillus strain TN.
  • the shuttle vector is pUBUC-IE as set forth in FIG. 5.
  • the shuttle vector will contain a PDC operon comprising a pdc gene and a adh gene under the control of the ldh promoter and operably linked to the IE sequence of FIG. 1.
  • a method of selecting for recombinant Bacillus sp at high temperature wherein plasmid DNA has been stably integrated into the ldh gene of the recombinant bacterium by homologous recombination comprising use of PCR to select for recombinants that do not contain the native ldh gene and E sequence.
  • successful integration of the insertion sequence into the ldh gene will be indicated by failure to amplify a PCR product from the ldh gene of the recombinant bacterium.
  • the present invention also provides one or more polypeptides encoded by the sequence shown in FIG. 1 from nucleotide 652 to nucleotide 3800, or a functional variant or portion thereof wherein the one or more polypeptides have the biological activity of a transposase.
  • the one or more polypeptides may have the biological activity of a transposase taken alone or when combined with other polypeptides.
  • the one or more polypeptides has the amino acid sequence shown in FIG. 13, FIG. 14 or FIG. 15 or a functional portion or variant thereof.
  • the functional portions or variants retain at least part of the transposase function of the polypeptide shown in FIG. 13, FIG. 14 or FIG. 15.
  • the portions are at least 20, more preferably at least 50 amino acids in length.
  • the variants have at least 80%, more preferably at least 90% and most preferably at least 95% sequence homology with the polypeptide shown in FIG. 13, FIG. 14 or FIG. 15. Homology is preferably measured using the BLAST program.
  • a seventh aspect of the present invention there is provided a DNA sequence as set forth in FIG. 7B, or a functional variant thereof, which codes for a polypeptide having the biological activity of the enzyme lactate permease.
  • functional variants include DNA sequences which as a result of sequence additions, deletions or substitutions, or which by virtue of the degeneracy of the genetic code, hybridise to and/or encode a polypeptide having a lactate dehydrogenase lactate permease or alcohol deydrongenase activity.
  • the variants have at least 80%, more preferably 90% and most preferably 95% sequence homology to the sequence shown in the Figures. Homology is preferably measured using the BLAST program.
  • a ninth aspect of the invention also provides a method for improving the stability of the ldh mutant comprising expressing genes using a pdc/adh operon.
  • a tenth aspect of the present invention relates to a technique for the integration and selection of recombinant Bacillus sp in accordance with the invention.
  • a process for the production of ethanol by bacterial fermentation of the Gram-positive bacterium of the present invention comprising optimised fermentation conditions of pH, temperature, redox values and specific dilution rates for cell growth and ethanol production.
  • the fermentation conditions will comprise a pH range of between 5.5-7.5 and a temperature range of 40-75° C. with redox values being between ⁇ 360-400 mV and dilution rates between 0.3 and 0.8 h ⁇ 1 .
  • FIG. 1 shows the nucleotide sequence of a DNA sequence comprising an insertion element (IE), wherein the IE sequence is underlined;
  • FIG. 2 is a schematic representation of the genetic instability of strain TN
  • FIG. 3 is a schematic representation of the method for LDH gene inactivation by single-crossover recombination in Bacillus mutant strain TN;
  • FIG. 4 is a graphical representation showing the stability of Bacillus mutant strain TN-T9 in continuous culture for over 750 hours;
  • FIG. 5 is a schematic representation of shuttle vector pUBUC-IE
  • FIG. 6 shows the DNA sequence of a novel lactate dehydrogenase gene and translated amino acid sequence from Bacillus strain LN;
  • FIG. 7A shows the partial DNA sequence of a novel lactate permease gene and the translated amino acid sequence from Bacillus strain LN;
  • FIG. 7B shows the full DNA sequence of a novel lactate permease gene and the translated amino acid sequence from Bacillus strain LN;
  • FIG. 8 shows the DNA sequence of a novel alcohol dehydrogenase gene (underlined) from Bacillus strain LN;
  • FIG. 9 is a schematic representation showing (A) the development of Bacillus strain TN-T9 and (B) the development of Bacillus strains TN-T9 and TN-TK;
  • FIG. 10 shows the construction of an artificial PDC operon
  • FIG. 11 shows the amino acid sequence of L-lactate dehydrogenase (ldh) from the TN strain
  • FIG. 12 shows the amino acid sequence of alcohol dehydrogenase (adh) from the TN strain
  • FIG. 13 shows the amino acid sequence of a transposase encoded by the IE sequence.
  • FIG. 14 shows the amino acid sequence of a transposase encoded by the IE sequence.
  • FIG. 15 shows the amino acid sequence of a transposase encoded by the IE sequence.
  • Plasmid pUB110 is a widely used vector that was isolated from Staphyloccocus aureus which confers resistance to kanamycin and which can replicate in B. stearothermophilus at temperatures up to 54° C. Narumi et al., 1992 Biotechnology Techniques 6, No. 1. Plasmids pUB 110 and pUC18 were linearised with EcoR1 and BamH1, and then ligated together to form pUBUC (6.4 kb). Plasmid pUBUC has a temperature sensitive replicon, and cannot replicate above 54° C. making it an ideal host for gene integration, via homologous recombination at elevated temperatures.
  • a 1.1 kb fragment containing the met gene was amplified from Haemophilus aeygptius chromosomal DNA by PCR. The gene was verified by DNA sequencing. The met gene was trimmed with BamHI and XbaI, and then subcloned into the expression plasmid pCL1920, previously linearised with BamH1and XbaI. The resultant plasmid pMETH was transformed into E. coli TOP10. E. coli TOP10 cells harbouring pMETH were propagated and the culture was harvested for subsequent transformation and in vivo methylation using a method described by Tang et al (1994) Nuc. Acid Res. 22 (14). Competent cells were stored in convenient aliquots at ⁇ 70° C. prior to transformation.
  • the IE sequence was amplified from TN chromosomal DNA by PCR using primers LDH7 and LDH8.
  • concentration of reactants and the PCR procedure used were those recommended in the ExpandTM High Fidelity PCR System (Roche Diagnostics).
  • PCR amplification from lyophilised cells was achieved after 30 cycles in a Genius thermocycler (Techne, Ltd., Cambridge).
  • the sequence of the upstream primer, LDH7 was 5′-AAGCTT GAT GAA ATC CGG ATT TGA TGG-3′ and the sequence of the downstream primer, LDH8 was 5′-TCTAGA GCT AAA TTT CCA AGT AGC-3′.
  • These primers were chosen from the ldh gene sequence that flanked the insertion sequence.
  • a HindIII restriction site was introduced into the upstream primer and a XbaI restriction site was introduced into the downstream primer to create convenient restriction sites for subsequent cloning (introduced sites are underlined).
  • pUBUC-IE The resulting shuttle plasmid, referred to as pUBUC-IE (FIG. 5) can replicate in E. coli and Bacillus strains at temperatures up to 54° C., confers resistance to ampicillin and kanamycin, and harbours the IE sequence from Bacillus strain TN.
  • Bacillus strain TN converts the intracellular metabolite pyruvate to acetyl-CoA via the PFL or PDH pathway. Acetyl-CoA is then reduced to acetaldehyde and then to ethanol in reactions catalysed by AcDH and ADH, respectively.
  • the introduction of a foreign PDC enzyme provides the cells with an alternative pathway for ethanol production that involves decarboxylation of pyruvate by PDC to form acetaldehyde which is then reduced to ethanol by the native ADH enzyme. Both PDC and ADH are involved in the conversion of pyruvate to ethanol.
  • Plasmid pUBUC-IE was methylated in vivo after transformation, propagation in and purification from E. coli TOP10 cells harbouring plasmid pMETH. Methylated pUBUC-IE was then used to transform Bacillus strain TN. Bacillus strain TN cells were grown at 65° C. in 50 ml of TGP medium until the absorbance at 600 nm (A 600 ) reached 0.5-0.6. The culture was chilled on ice for 15-30 min. The cells were harvested by centrifugation and washed once in 10 ml and twice in 5 ml of cold TH buffer (272 mM trehalose and 8 mM HEPES; pH 7.5 with KOH).
  • the cell pellet was re-suspended in 400 ⁇ l of TH buffer and stored at 4° C. prior to electroporation.
  • Methylated plasmid DNA was used to transform strain TN by electroporation based on a method previously described by Narumi et al (1992) Biotechnology Techniques 6(1).
  • the competent cells were dispensed into 90 ⁇ l aliquots and mixed with 2 ⁇ l of methylated plasmid DNA (250 ng/ ⁇ l). The mixture was transferred to cold electroporation cuvettes (0.2 cm electrode gap) and incubated on ice for 5 minutes.
  • the cells were immediately transferred to 5 ml of pre-warmed TGP, incubated at 52° C. for 1 hr, and plated on TGP agar (10 ⁇ g/ml kanamycin). The plates were incubated for 24-48 hours at 52° C.
  • TN integrants were isolated at 68° C. Failure to amplify a PCR product using LDH primers in TN integrants indicated that at least one copy of plasmid pUBUC-IE had become integrated into the chromosome. As a result of integration the new strain TN-T9 was found to be more stable with regard to ldh reversion and “take over” than the parental strain TN.
  • Bacillus TN-TK is a kanamycin sensitive derivative of TN-T9. This strain is completely stable with regard to the ldh mutation and an ideal host for plasmid borne expression involving kanamycin as a selectable marker.
  • TN-T9 was first grown at 68° C. for 24 hours in 5 ml of TGP supplemented with kanamycin (10 ⁇ g/ml). Approximately 100 ml of culture was spread on two TGP (Km) agar plates and incubated overnight at 68° C. Several hundred colonies were obtained and 100 were transferred to fresh TGP (Km) plates using a sterile toothpick. After overnight growth at 68° C., the colonies were transferred (by replica plating) to fresh TGP plates and TGP (Km) plates and grown overnight at 68C.
  • kanamycin sensitive colonies were obtained on TGP but not on the corresponding TGP (Km) plate.
  • the ldh gene regions from these colonies were amplified by PCR and found to be comparable in size to the disrupted ldh gene from TN-T9 (parental strain).
  • PCR was used to demonstrate that the strains had lost the gene conferring resistance to kanamycin.
  • One derivative referred to as TN-TK was chosen for further growth experiments. These experiments confirmed that the kanamycin sensitivity and ldh mutation were completely stable.

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Cited By (5)

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US20070026104A1 (en) * 2003-03-12 2007-02-01 Shigeru Nakano Alcohol dehydrogenase gene of acetic acid bacterium
US20090042265A1 (en) * 2005-05-04 2009-02-12 Anthony Atkinson Thermophilic Microorganisms with Inactivated Lactate Dehydrogenase Gene (LDH) for Ethanol Production
US20090246841A1 (en) * 2008-03-26 2009-10-01 Jamieson Andrew C Methods and compositions for production of acetaldehyde
US20120301937A1 (en) * 2010-01-26 2012-11-29 Scale Biofuel, ApS Methods for producing and harvesting ethanol and apparatus for producing and harvesting the same
EP3279329A1 (de) 2006-07-21 2018-02-07 Xyleco, Inc. Systeme zur umwandlung von biomasse

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WO2009078973A2 (en) * 2007-12-13 2009-06-25 Glycos Biotechnologies, Incorporated Microbial conversion of oils and fatty acids to high-value chemicals
NZ600509A (en) 2009-12-29 2014-08-29 Butamax Tm Advanced Biofuels Alcohol dehydrogenases (adh) useful for fermentive production of lower alkyl alcohols
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US8097460B2 (en) 2012-01-17
CN1798846A (zh) 2006-07-05
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