Biomedical subjects

George N Bennett

Publications and source records attributed to George N Bennett.

At least 37 records · Page 2Linked to original sources

PubMed2005

Characterization of thermostable Xyn10A enzyme from mesophilic Clostridium acetobutylicum ATCC 824.

A thermostable xylanase gene, xyn10A (CAP0053), was cloned from Clostridium acetobutylicum ATCC 824. The nucleotide sequence of the C. acetobutylicum xyn10A gene encoded a 318-amino-acid, single-domain, family 10 xylanase, Xyn10A, with a molecular mass of 34 kDa. Xyn10A exhibited extremely high (92%) amino acid sequence identity with Xyn10B (CAP0116) of this strain and had 42% and 32% identity with the catalytic domains of Rhodothermus marinus xylanase I and Thermoascus aurantiacus xylanase I, respectively. Xyn10A enzyme was purified from recombinant Escherichia coli and was highly active toward oat-spelt and Birchwood xylan and slightly active toward carboxymethyl cellulose, arabinogalactouronic acid, and various p-nitrophenyl monosaccharides. Xyn10A hydrolyzed xylan and xylooligosaccharides larger than xylobiose to produce xylose. This enzyme was optimally active at 60 degrees C and had an optimum pH of 5.0. This is one of a number of related activities encoded on the large plasmid in this strain.

Amino Acid Sequence↗

PubMed2005

Biodegradation of xenobiotics by anaerobic bacteria.

Xenobiotic biodegradation under anaerobic conditions such as in groundwater, sediment, landfill, sludge digesters and bioreactors has gained increasing attention over the last two decades. This review gives a broad overview of our current understanding of and recent advances in anaerobic biodegradation of five selected groups of xenobiotic compounds (petroleum hydrocarbons and fuel additives, nitroaromatic compounds and explosives, chlorinated aliphatic and aromatic compounds, pesticides, and surfactants). Significant advances have been made toward the isolation of bacterial cultures, elucidation of biochemical mechanisms, and laboratory and field scale applications for xenobiotic removal. For certain highly chlorinated hydrocarbons (e.g., tetrachlorethylene), anaerobic processes cannot be easily substituted with current aerobic processes. For petroleum hydrocarbons, although aerobic processes are generally used, anaerobic biodegradation is significant under certain circumstances (e.g., O(2)-depleted aquifers, oil spilled in marshes). For persistent compounds including polychlorinated biphenyls, dioxins, and DDT, anaerobic processes are slow for remedial application, but can be a significant long-term avenue for natural attenuation. In some cases, a sequential anaerobic-aerobic strategy is needed for total destruction of xenobiotic compounds. Several points for future research are also presented in this review.

Aerobiosis↗

PubMed2005

Genetic reconstruction of the aerobic central metabolism in Escherichia coli for the absolute aerobic production of succinate.

Most reported efforts to enhance production of the industrially valuable specialty chemical succinate have been done under anaerobic conditions, where E. coli undergoes mixed-acid fermentation. These efforts have often been hampered by the limitations of NADH availability, poor cell growth, and slow production. An aerobic succinate production system was strategically designed that allows E. coli to produce and accumulate succinate efficiently and substantially as a product under absolute aerobic conditions. Mutations in the tricarboxylic acid cycle (sdhAB, icd, iclR) and acetate pathways (poxB, ackA-pta) of E. coli were created to construct the glyoxylate cycle for aerobic succinate production. Experiments in flask studies showed that 14.28 mM of succinate could be produced aerobically with a yield of 0.344 mole/mole using 55 mM glucose. In aerobic batch reactor studies, succinate production rate was faster, reaching 0.5 mole/mole in 24 h with a concentration of 22.12 mM; further cultivation showed that succinate production reached 43 mM with a yield of 0.7. There was also substantial pyruvate and TCA cycle C(6) intermediate accumulation in the mutant. The results suggest that more metabolic engineering improvements can be made to this system to make aerobic succinate production more efficient. Nevertheless, this aerobic succinate production system provides the first platform for enhancing succinate production aerobically in E. coli based on the creation of a new aerobic central metabolic network.

Aerobiosis↗

PubMed2005

Metabolic engineering of aerobic succinate production systems in Escherichia coli to improve process productivity and achieve the maximum theoretical succinate yield.

The potential to produce succinate aerobically in Escherichia coli would offer great advantages over anaerobic fermentation in terms of faster biomass generation, carbon throughput, and product formation. Genetic manipulations were performed on two aerobic succinate production systems to increase their succinate yield and productivity. One of the aerobic succinate production systems developed earlier (Biotechnol, Bioeng., 2004, accepted) was constructed with five mutations (DeltasdhAB, Deltaicd, DeltaiclR, DeltapoxB, and Delta(ackA-pta)), which created a highly active glyoxylate cycle. In this study, a second production system was constructed with four of the five above mutations (DeltasdhAB, DeltaiclR, DeltapoxB, and Delta(ackA-pta)). This system has two routes in the aerobic central metabolism for succinate production. One is the glyoxylate cycle and the other is the oxidative branch of the TCA cycle. Inactivation of ptsG and overexpression of a mutant Sorghum pepc in these two production systems showed that the maximum theoretical succinate yield of 1.0 mol/mol glucose consumed could be achieved. Furthermore, the two-route production system with ptsG inactivation and pepc overexpression demonstrated substantially higher succinate productivity than the previous system, a level unsurpassed for aerobic succinate production. This optimized system showed remarkable potential for large-scale aerobic succinate production and process optimization.

Citric Acid Cycle↗

PubMed2005

Novel pathway engineering design of the anaerobic central metabolic pathway in Escherichia coli to increase succinate yield and productivity.

A novel in vivo method of producing succinate has been developed. A genetically engineered Escherichia coli strain has been constructed to meet the NADH requirement and carbon demand to produce high quantities and yield of succinate by strategically implementing metabolic pathway alterations. Currently, the maximum theoretical succinate yield under strictly anaerobic conditions through the fermentative succinate biosynthesis pathway is limited to one mole per mole of glucose due to NADH limitation. The implemented strategic design involves the construction of a dual succinate synthesis route, which diverts required quantities of NADH through the traditional fermentative pathway and maximizes the carbon converted to succinate by balancing the carbon flux through the fermentative pathway and the glyoxylate pathway (which has less NADH requirement). The synthesis of succinate uses a combination of the two pathways to balance the NADH. Consequently, experimental results indicated that these combined pathways gave the most efficient conversion of glucose to succinate with the highest yield using only 1.25 moles of NADH per mole of succinate in contrast to the sole fermentative pathway, which uses 2 moles of NADH per mole of succinate. A recombinant E. coli strain, SBS550MG, was created by deactivating adhE, ldhA and ack-pta from the central metabolic pathway and by activating the glyoxylate pathway through the inactivation of iclR, which encodes a transcriptional repressor protein of the glyoxylate bypass. The inactivation of these genes in SBS550MG increased the succinate yield from glucose to about 1.6 mol/mol with an average anaerobic productivity rate of 10 mM/h (approximately 0.64 mM/h-OD600). This strain is capable of fermenting high concentrations of glucose in less than 24 h. Additional derepression of the glyxoylate pathway by inactivation of arcA, leading to a strain designated as SBS660MG, did not significantly increase the succinate yield and it decreased glucose consumption by 80%. It was also observed that an adhE, ldhA and ack-pta mutant designated as SBS990MG, was able to achieve a high succinate yield similar to SBS550MG when expressing a Bacillus subtilis NADH-insensitive citrate synthase from a plasmid.

Anaerobiosis↗

PubMed2005

Intracellular butyryl phosphate and acetyl phosphate concentrations in Clostridium acetobutylicum and their implications for solvent formation.

It has been suggested (L. H. Harris, R. P. Desai, N. E. Welker, and E. T. Papoutsakis, Biotechnol. Bioeng. 67:1-11, 2000) that butyryl phosphate (BuP) is a regulator of solventogenesis in Clostridium acetobutylicum. Here, we determined BuP and acetyl phosphate (AcP) levels in fermentations of C. acetobutylicum wild type (WT), degenerate strain M5, a butyrate kinase (buk) mutant, and a phosphotransacetylase (pta) mutant. A sensitive method was developed to measure BuP and AcP in the same sample. Compared to the WT, the buk mutant had higher levels of BuP and AcP; the BuP levels were high during the early exponential phase, and there was a peak corresponding to solvent production. Consistent with this, solvent formation was initiated significantly earlier and was much stronger in the buk mutant than in all other strains. For all strains, initiation of butanol formation corresponded to a BuP peak concentration that was more than 60 to 70 pmol/g (dry weight), and higher and sustained levels corresponded to higher butanol formation fluxes. The BuP levels never exceeded 40 to 50 pmol/g (dry weight) in strain M5, which produces no solvents. The BuP profiles were bimodal, and there was a second peak midway through solventogenesis that corresponded to carboxylic acid reutilization. AcP showed a delayed single peak during late solventogenesis corresponding to acetate reutilization. As expected, in the pta mutant the AcP levels were very low, yet this strain exhibited strong butanol production. These data suggest that BuP is a regulatory molecule that may act as a phosphodonor of transcriptional factors. DNA array-based transcriptional analysis of the buk and M5 mutants demonstrated that high BuP levels corresponded to downregulation of flagellar genes and upregulation of solvent formation and stress genes.

Bacterial Proteins↗

PubMed2005

Expression of abrB310 and SinR, and effects of decreased abrB310 expression on the transition from acidogenesis to solventogenesis, in Clostridium acetobutylicum ATCC 824.

The transcription factors sinR and abrB are involved in the control of sporulation initiation in Bacillus subtilis. We identified a single homologue to sinR and three highly similar homologues to abrB, designated abrB310, abrB1941, and abrB3647, in Clostridium acetobutylicum ATCC 824. Using reporter vectors, we showed that the promoters of abrB1941 and abrB3647 were not active under the growth conditions tested. The abrB310 promoter was strongly active throughout growth and exhibited a transient elevation of expression at the onset of solventogenesis. Primer extension assays showed that two transcripts of abrB310 and a single, extremely weak transcript for sinR are expressed. Potential -35 and -10 consensus motifs are readily identifiable surrounding the transcription start sites of abrB310 and sinR, with a single putative 0A box present within the promoter of abrB310. In strains of C. acetobutylicum transformed with plasmids to elevate sinR expression or decrease sinR expression, no significant differences in growth or in acid or solvent production were observed compared to the control strains. In C. acetobutylicum strain 824(pAS310), which expressed an antisense RNA construct targeted against abrB310, the acids acetate and butyrate accumulated to approximately twice the normal concentration. This accumulation corresponded to a delay and decrease in acetone and butanol production. It was also found that sporulation in strain 824(pAS310) was delayed but that the morphology of sporulating cells and spores was normal. Based upon these observations, we propose that abrB310 may act as a regulator at the transition between acidogenic and solventogenic growth.

Acetates↗

PubMed2005

SpoIIE regulates sporulation but does not directly affect solventogenesis in Clostridium acetobutylicum ATCC 824.

Using gene expression reporter vectors, we examined the activity of the spoIIE promoter in wild-type and spo0A-deleted strains of Clostridium acetobutylicum ATCC 824. In wild-type cells, the spoIIE promoter is active in a transient manner during late solventogenesis, but in strain SKO1, where the sporulation initiator spo0A is disrupted, no spoIIE promoter activity is detectable at any stage of growth. Strains 824(pMSpo) and 824(pASspo) were created to overexpress spoIIE and to decrease spoIIE expression via antisense RNA targeted against spoIIE, respectively. Some cultures of strains 824(pMSpo) degenerated during fermentations by losing the pSOL1 megaplasmid and hence did not produce the solvents ethanol, acetone, and butanol. The frequent degeneration event was shown to require an intact copy of spoIIE. Nondegenerate cultures of 824(pMSpo) exhibited normal growth and solvent production. Strain 824(pASspo) exhibited prolonged solventogenesis characterized by increased production of ethanol (225%), acetone (43%), and butanol (110%). Sporulation in strains harboring pASspo was significantly delayed, with sporulating cells exhibiting altered morphology. These results suggest that SpoIIE has no direct effect on the control of solventogenesis and that the changes in solvent production in spoIIE-downregulated cells are mediated by effects on the cell during sporulation.

Bacterial Proteins↗

PubMed2004

Effect of Sorghum vulgare phosphoenolpyruvate carboxylase and Lactococcus lactis pyruvate carboxylase coexpression on succinate production in mutant strains of Escherichia coli.

Sorghum vulgare phosphoenolpyruvate carboxylase (PEPC) and Lactococcus lactis pyruvate carboxylase (PYC) were overexpressed in Escherichia coli concurrently to improve the production of succinate, a valuable industrial specialty chemical. This coexpression system was also applied to E. coli mutant strains strategically designed by inactivating the competing pathways of succinate formation. The highest level of succinate production was observed in E. coli strains coexpressing both PEPC and PYC when compared with E. coli strains individually overexpressing either PEPC or PYC. Lactate production was also significantly reduced with PEPC and PYC coexpression. Lactate and acetate pathways were inactivated to eliminate the competing pathways of succinate formation. Results showed that inactivation of both the lactate and acetate pathways with the coexpression of PEPC and PYC was most effective in improving succinate production. Inactivating the lactate or acetate pathway alone only caused a majority of the carbon flux to shift to other metabolites rather than succinate. Coexpression of PEPC and PYC was also applied to an E. coli mutant strain deficient in lactate dehydrogenase and pyruvate:formate lyase that accumulated a substantial amount of the intermediate metabolite pyruvate during growth. Results showed that PEPC and PYC coexpression was effective in depleting pyruvate accumulation and increasing the production of metabolites.

Biotechnology↗

PubMed2004

Thermostable xylanase10B from Clostridium acetobutylicum ATCC824.

The Clostridium acetobutylicum xylanase gene xyn10B (CAP0116) was cloned from the type strain ATCC 824, whose genome was recently sequenced. The nucleotide sequence of C. acetobutylicum xyn10B encodes a 318-amino acid protein. Xyn10B consists of a single catalytic domain that belongs to family 10 of glycosyl hydrolases. The enzyme was purified from recombinant Escherichia coli. The Xyn10B enzyme was highly active toward birchwood xylan, oat-spelt xylan, and moderately active toward avicel, carboxymethyl cellulose, polygalacturonic acid, lichenan, laminarin, barley-beta-glucan and various p-nitrophenyl monosaccharides. Xyn10B hydrolyzed xylan and xylooligosaccharides to produce xylobiose and xylotriose. The pH optimum of Xyn10B was 5.0, and the optimal temperature was 70 degrees C. The enzyme was stable at 60 degrees C at pH 5.0-6.5 for 1 h without substrate. This is one of a number of xylan-related activities encoded on the large plasmid in C. acetobutylicum ATCC 824.

Cloning, Molecular↗

PubMed2004

Cofactor engineering of intracellular CoA/acetyl-CoA and its effect on metabolic flux redistribution in Escherichia coli.

Coenzyme A (CoA) and its thioester derivatives are important cofactors participating in over 100 different reactions in intermediary metabolism of microorganisms. The time profiles of intracellular CoA and acetyl-CoA levels were studied in an aerobic batch reactor. The CoA level starts at a high value and falls off gradually over the exponential and stationary growth phases, reaching negligible levels at the end of 24h. The acetyl-CoA level, on the other hand, increases initially reaching a maximum and decreases gradually reaching negligible levels after 24h. Overexpressing one of the upstream rate-controlling enzyme the pantothenate kinase with simultaneous supplementation of the precursor pantothenic acid to the culture medium increased the intracellular CoA/acetyl-CoA levels. It was found that supplementation of the precursor pantothenic acid is essential to increase CoA/acetyl-CoA levels. A 10-fold increase in CoA level was observed upon this overexpression in complex medium. Acetyl-CoA levels also increased (5-fold) but not as much as CoA, leaving much of the CoA in free unacetylated form. The increase in intracellular CoA/acetyl-CoA levels led to an increase in carbon flux to the acetate production pathway leading to formation of more acetate in complex medium, whereas no such change in metabolite redistribution was observed in minimal medium.

Acetates↗

PubMed2004

Applicability of CoA/acetyl-CoA manipulation system to enhance isoamyl acetate production in Escherichia coli.

Coenzyme A (CoA) and its thioester derivatives are important precursor molecules for many industrially useful compounds such as esters, PHBs, lycopene and polyketides. Previously, in our lab we could increase the intracellular levels of CoA and acetyl-Coenzyme A (acetyl-CoA) by overexpressing one of the upstream rate-controlling enzymes pantothenate kinase with a concomitant supplementation of the precursor pantothenic acid to the cell culture medium. In this study, we showed that the CoA/acetyl-CoA manipulation system could be used to increase the productivity of industrially useful compounds derived from acetyl-CoA. We chose the production of isoamyl acetate as a model system. Isoamyl acetate is an important flavor component of sake yeast and holds a great commercial value. Alcohol acetyl transferase (AAT) condenses isoamyl alcohol and acetyl-CoA to produce isoamyl acetate. The gene ATF2, coding for this AAT was cloned and expressed in Escherichia coli. This genetic engineered E. coli produces isoamyl acetate, an ester, from intracellular acetyl-CoA when isoamyl alcohol is added externally to the cell culture medium. In the current study, we showed that in a strain bearing ATF2 gene, an increase in intracellular CoA/acetyl-CoA by overexpressing panK leads to an increase in isoamyl acetate production. Additionally, the cofactor manipulation technique was combined with more traditional approach of competing pathway deletions to further increase isoamyl acetate production. The acetate production pathway competes with isoamyl acetate production for the common intracellular metabolite acetyl-CoA. Earlier we have shown that acetate pathway deletion (ackA-pta) increases isoamyl acetate production. The acetate production pathway was inactivated under elevated CoA/acetyl-CoA conditions, which lead to a further increase in isoamyl acetate production.

Acetyl Coenzyme A↗

PubMed2003

Role of hydroxylamine intermediates in the phytotransformation of 2,4,6-trinitrotoluene by Myriophyllum aquaticum.

Phytotransformation studies of 2,4,6-trinitrotoluene (TNT) were conducted using Myriophyllum aquaticum to clarify the role of initial intermediates of TNT transformation in the complex product distributions reported previously. 2-Hydroxylamino-4,6-dinitrotoluene (2HA46DNT) and 4-hydroxylamino-2,6-dinitrotoluene (4HA26DNT) were the initial intermediates of TNT phytotransformation. 2HA46DNT and 4HA26DNT were both abiotically transformed to 4,4',6,6'-tetranitro-2,2'-azoxytoluene (2,2'azoxy) and 2,2',6,6'-tetranitro-4,4'-azoxytoluene (4,4'azoxy) and also phytoreduced to the related amines 2-amino-4,6-dinitrotoluene (2A46DNT) and 4-amino-2,6-dinitrotoluene (4A26DNT). To further elucidate the initial steps of this TNT phytotransformation pathway, the transformations of known intermediates (including 2HA46DNT, 4HA26DNT, 2A46DNT, 4A26DNT, 2,2'azoxy, and 4,4'azoxy) were monitored in plant systems. The transformation rates were measured, and kinetic analysis using pseudo-first-order models was used to evaluate the relative rates of competing reactions. The formation of the azoxy products was determined to be more rapid than the formation of the amine products. Both the azoxy and amine products were subject to uptake and further transformation by the plant.

Biodegradation, Environmental↗

PubMed2003

Heterologous expression of the Saccharomyces cerevisiae alcohol acetyltransferase genes in Clostridium acetobutylicum and Escherichia coli for the production of isoamyl acetate.

Esters are formed by the condensation of acids with alcohols. The esters isoamyl acetate and butyl butyrate are used for food and beverage flavorings. Alcohol acetyltransferase is one enzyme responsible for the production of esters from acetyl-CoA and different alcohol substrates. The genes ATF1 and ATF2, encoding alcohol acetyltransferases from the yeast Saccharomyces cerevisiae have been sequenced and characterized. The production of acids and alcohols in mass quantities by the industrially important Clostridium acetobutylicum makes it a potential organism for exploitation of alcohol acetyltransferase activity. This report focuses on the heterologous expression of the alcohol acetyltransferases in Escherichia coli and C. acetobutylicum. ATF1 and ATF2 were cloned and expressed in E. coli and ATF2 was expressed in C. acetobutylicum. Isoamyl acetate production from the substrate isoamyl alcohol in E. coli and C. acetobutylicum cultures was determined by head-space gas analysis. Alcohol acetyltransferase I produced more than twice as much isoamyl acetate as alcohol acetyltransferase II when expressed from a high-copy expression vector. The effect of substrate levels on ester production was explored in the two bacterial hosts to demonstrate the efficacy of utilizing ATF1 and ATF2 in bacteria for ester production.

Acetyltransferases↗

PubMed2003

Sequences affecting the regulation of solvent production in Clostridium acetobutylicum.

The high solvent phenotype of Clostridium acetobutylicum mutants B and H was complemented by the introduction of a plasmid that contains either an intact or partially-deleted copy of solR, restoring acetone and butanol production to wild-type levels. This demonstrates that the solR open reading frame on pSOLThi is not required to restore solvent levels. The promoter region upstream of alcohol dehydrogense E (adhE) was examined in efforts to identify sites that play major roles in the control of expression. A series of adhE promoter fragments was constructed and the expression of each in acid- and solvent-phases of growth was analyzed using a chloramphenicol acetyl-transferase reporter system. Our results show that a region beyond the 0A box is needed for full induction of the promoter. Additionally, we show that the presence of sequences around a possible processing site designated S2 may have a negative role in the regulation of adhE expression.

Acetone↗

PubMed2003

The effect of carbon sources and lactate dehydrogenase deletion on 1,2-propanediol production in Escherichia coli.

In previous studies, we showed that cofactor manipulations can potentially be used as a tool in metabolic engineering. In this study, sugars similar to glucose, that can feed into glycolysis and pyruvate production, but with different oxidation states, were used as substrates. This provided a simple way of testing the effect of manipulating the NADH/NAD+ ratio or the availability of NADH on the metabolic patterns of Escherichia coli under anaerobic conditions and on the production of 1,2-propanediol (1,2-PD), which requires NADH for its synthesis. Production of 1,2-PD was achieved by overexpressing the two enzymes methylglyoxal synthase from Clostridium acetobutylicum and glycerol dehydrogenase from E. coli. In addition, the effect of eliminating a pathway competing for NADH by using a ldh(-) strain (without lactate dehydrogenase activity) on the production of 1,2-PD was investigated. The oxidation state of the carbon source significantly affected the yield of metabolites, such as ethanol, acetate and lactate. However, feeding a more reduced carbon source did not increase the yield of 1,2-PD. The production of 1,2-PD with glucose as the carbon source was improved by the incorporation of a ldh(-) mutation. The results of these experiments indicate that our current 1,2-PD production system is not limited by NADH, but rather by the pathways following the formation of methylglyoxal.

Carbon↗

PubMed2003

2,4,6-trinitrotoluene reduction by an Fe-only hydrogenase in Clostridium acetobutylicum.

The role of hydrogenase on the reduction of 2,4,6-trinitrotoluene (TNT) in Clostridium acetobutylicum was evaluated. An Fe-only hydrogenase was isolated and identified by using TNT reduction activity as the selection basis. The formation of hydroxylamino intermediates by the purified enzyme corresponded to expected products for this reaction, and saturation kinetics were determined with a K(m) of 152 micro M. Comparisons between the wild type and a mutant strain lacking the region encoding an alternative Fe-Ni hydrogenase determined that Fe-Ni hydrogenase activity did not significantly contribute to TNT reduction. Hydrogenase expression levels were altered in various strains, allowing study of the role of the enzyme in TNT reduction rates. The level of hydrogenase activity in a cell system correlated (R(2) = 0.89) with the organism's ability to reduce TNT. A strain that overexpressed the hydrogenase activity resulted in maintained TNT reduction during late growth phases, which it is not typically observed in wild type strains. Strains exhibiting underexpression of hydrogenase produced slower TNT rates of reduction correlating with the determined level of expression. The isolated Fe-only hydrogenase is the primary catalyst for reducing TNT nitro substituents to the corresponding hydroxylamines in C. acetobutylicum in whole-cell systems. A mechanism for the reaction is proposed. Due to the prevalence of hydrogenase in soil microbes, this research may enhance the understanding of nitroaromatic compound transformation by common microbial communities.

Clostridium↗

PubMed2003

Expression of a cloned cyclopropane fatty acid synthase gene reduces solvent formation in Clostridium acetobutylicum ATCC 824.

The cyclopropane fatty acid synthase gene (cfa) of Clostridium acetobutylicum ATCC 824 was cloned and overexpressed under the control of the clostridial ptb promoter. The function of the cfa gene was confirmed by complementation of an Escherichia coli cfa-deficient strain in terms of fatty acid composition and growth rate under solvent stress. Constructs expressing cfa were introduced into C. acetobutylicum hosts and cultured in rich glucose broth in static flasks without pH control. Overexpression of the cfa gene in the wild type and in a butyrate kinase-deficient strain increased the cyclopropane fatty acid content of early-log-phase cells as well as initial acid and butanol resistance. However, solvent production in the cfa-overexpressing strain was considerably decreased, while acetate and butyrate levels remained high. The findings suggest that overexpression of cfa results in changes in membrane properties that dampen the full induction of solventogenesis. The overexpression of a marR homologous gene preceding the cfa gene in the clostridial genome resulted in reduced cyclopropane fatty acid accumulation.

1-Propanol↗