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Increased hydrogen production by genetic engineering of Escherichia coli.

Fan Z, Yuan L, Chatterjee R - PLoS ONE (2009)

Bottom Line: The specific hydrogen yield from glucose was improved by the modification of transcriptional regulators and metabolic enzymes involved in the dissimilation of pyruvate and formate.The expression of the global transcriptional regulator protein FNR at levels above natural abundance had a synergistic effect on increasing the hydrogen yield in the DeltafocA genetic background.The modification of global transcriptional regulators to modulate the expression of multiple operons required for the biosynthesis of formate hydrogenlyase represents a practical approach to improve hydrogen production.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant and Soil Sciences and Kentucky Tobacco Research and Development Center, University of Kentucky, Lexington, KY, USA.

ABSTRACT
Escherichia coli is capable of producing hydrogen under anaerobic growth conditions. Formate is converted to hydrogen in the fermenting cell by the formate hydrogenlyase enzyme system. The specific hydrogen yield from glucose was improved by the modification of transcriptional regulators and metabolic enzymes involved in the dissimilation of pyruvate and formate. The engineered E. coli strains ZF1 (DeltafocA; disrupted in a formate transporter gene) and ZF3 (DeltanarL; disrupted in a global transcriptional regulator gene) produced 14.9, and 14.4 micromols of hydrogen/mg of dry cell weight, respectively, compared to 9.8 micromols of hydrogen/mg of dry cell weight generated by wild-type E. coli strain W3110. The molar yield of hydrogen for strain ZF3 was 0.96 mols of hydrogen/mol of glucose, compared to 0.54 mols of hydrogen/mol of glucose for the wild-type E. coli strain. The expression of the global transcriptional regulator protein FNR at levels above natural abundance had a synergistic effect on increasing the hydrogen yield in the DeltafocA genetic background. The modification of global transcriptional regulators to modulate the expression of multiple operons required for the biosynthesis of formate hydrogenlyase represents a practical approach to improve hydrogen production.

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The genetic modification of metabolic pathways and regulatory components for hydrogen production in E. coli.The metabolic flows are indicated by solid arrows. Some key enzyme systems are labeled. The key global regulators and their regulatory targets are circled and indicated by dashed arrows, respectively. Pluses (+) represent activation, and minuses (−) represent repression. Crosses (X) indicate chromosomal gene disruptions.
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pone-0004432-g001: The genetic modification of metabolic pathways and regulatory components for hydrogen production in E. coli.The metabolic flows are indicated by solid arrows. Some key enzyme systems are labeled. The key global regulators and their regulatory targets are circled and indicated by dashed arrows, respectively. Pluses (+) represent activation, and minuses (−) represent repression. Crosses (X) indicate chromosomal gene disruptions.

Mentions: The production of hydrogen by facultative anaerobic organisms such as E. coli is a characteristic of mixed acid fermentation. Under anaerobic conditions, the fermentation products comprise a mixture of ethanol, succinate, lactate, acetate, and formate (Fig. 1). Succinate is produced via the succinate pathway. A key reaction in this pathway is carboxylation of phosphoenolpyruvate (PEP) to the four-carbon compound oxaloacetate by phosphoenolpyruvate carboxylase (PEPC) [6]. PEP is also converted to pyruvate which is subsequently converted to acetyl-CoA and formate by pyruvate formate lyase (PFL), and to lactate by lactate dehydrogenase (LDH). Formate hydrogenlyase (FHL) catalyzes the conversion of formate to carbon dioxide and hydrogen [7], [8]. The intracellular level of formate is determined by the rates of biosynthesis and metabolism of formate, and also by formate transporter FocA which is a membrane protein involved in formate transport into and out of the cell [9]. Knockout of the focA gene results in intracellular accumulation of formate [10]. The FHL enzyme complex is comprised of formate dehydrogenase H (FDHH), and a hydrogen-evolving hydrogenase (hydrogenase 3) [11], [12]. The biosynthesis of PFL and FHL are up-regulated by the action of multiple transcriptional regulators including the global transcriptional factors Fnr, ArcAB and integration host factor (IHF) [13]–[15], and repressed by the dual transcriptional regulator NarL (Table 1)[16]. The transcription of the fhl regulon is regulated by the primary and secondary transcriptional activator FHLA and ModE [17], [18]. The expression of fhlA is activated by Fnr in response to the cellular redox state [19], [20]. The biosynthesis of FDHH also requires the expression of selC gene which encodes a tRNA for the incorporation of selenocysteine to FDHH (Table 1) [8], [11], [21].


Increased hydrogen production by genetic engineering of Escherichia coli.

Fan Z, Yuan L, Chatterjee R - PLoS ONE (2009)

The genetic modification of metabolic pathways and regulatory components for hydrogen production in E. coli.The metabolic flows are indicated by solid arrows. Some key enzyme systems are labeled. The key global regulators and their regulatory targets are circled and indicated by dashed arrows, respectively. Pluses (+) represent activation, and minuses (−) represent repression. Crosses (X) indicate chromosomal gene disruptions.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2636881&req=5

pone-0004432-g001: The genetic modification of metabolic pathways and regulatory components for hydrogen production in E. coli.The metabolic flows are indicated by solid arrows. Some key enzyme systems are labeled. The key global regulators and their regulatory targets are circled and indicated by dashed arrows, respectively. Pluses (+) represent activation, and minuses (−) represent repression. Crosses (X) indicate chromosomal gene disruptions.
Mentions: The production of hydrogen by facultative anaerobic organisms such as E. coli is a characteristic of mixed acid fermentation. Under anaerobic conditions, the fermentation products comprise a mixture of ethanol, succinate, lactate, acetate, and formate (Fig. 1). Succinate is produced via the succinate pathway. A key reaction in this pathway is carboxylation of phosphoenolpyruvate (PEP) to the four-carbon compound oxaloacetate by phosphoenolpyruvate carboxylase (PEPC) [6]. PEP is also converted to pyruvate which is subsequently converted to acetyl-CoA and formate by pyruvate formate lyase (PFL), and to lactate by lactate dehydrogenase (LDH). Formate hydrogenlyase (FHL) catalyzes the conversion of formate to carbon dioxide and hydrogen [7], [8]. The intracellular level of formate is determined by the rates of biosynthesis and metabolism of formate, and also by formate transporter FocA which is a membrane protein involved in formate transport into and out of the cell [9]. Knockout of the focA gene results in intracellular accumulation of formate [10]. The FHL enzyme complex is comprised of formate dehydrogenase H (FDHH), and a hydrogen-evolving hydrogenase (hydrogenase 3) [11], [12]. The biosynthesis of PFL and FHL are up-regulated by the action of multiple transcriptional regulators including the global transcriptional factors Fnr, ArcAB and integration host factor (IHF) [13]–[15], and repressed by the dual transcriptional regulator NarL (Table 1)[16]. The transcription of the fhl regulon is regulated by the primary and secondary transcriptional activator FHLA and ModE [17], [18]. The expression of fhlA is activated by Fnr in response to the cellular redox state [19], [20]. The biosynthesis of FDHH also requires the expression of selC gene which encodes a tRNA for the incorporation of selenocysteine to FDHH (Table 1) [8], [11], [21].

Bottom Line: The specific hydrogen yield from glucose was improved by the modification of transcriptional regulators and metabolic enzymes involved in the dissimilation of pyruvate and formate.The expression of the global transcriptional regulator protein FNR at levels above natural abundance had a synergistic effect on increasing the hydrogen yield in the DeltafocA genetic background.The modification of global transcriptional regulators to modulate the expression of multiple operons required for the biosynthesis of formate hydrogenlyase represents a practical approach to improve hydrogen production.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant and Soil Sciences and Kentucky Tobacco Research and Development Center, University of Kentucky, Lexington, KY, USA.

ABSTRACT
Escherichia coli is capable of producing hydrogen under anaerobic growth conditions. Formate is converted to hydrogen in the fermenting cell by the formate hydrogenlyase enzyme system. The specific hydrogen yield from glucose was improved by the modification of transcriptional regulators and metabolic enzymes involved in the dissimilation of pyruvate and formate. The engineered E. coli strains ZF1 (DeltafocA; disrupted in a formate transporter gene) and ZF3 (DeltanarL; disrupted in a global transcriptional regulator gene) produced 14.9, and 14.4 micromols of hydrogen/mg of dry cell weight, respectively, compared to 9.8 micromols of hydrogen/mg of dry cell weight generated by wild-type E. coli strain W3110. The molar yield of hydrogen for strain ZF3 was 0.96 mols of hydrogen/mol of glucose, compared to 0.54 mols of hydrogen/mol of glucose for the wild-type E. coli strain. The expression of the global transcriptional regulator protein FNR at levels above natural abundance had a synergistic effect on increasing the hydrogen yield in the DeltafocA genetic background. The modification of global transcriptional regulators to modulate the expression of multiple operons required for the biosynthesis of formate hydrogenlyase represents a practical approach to improve hydrogen production.

Show MeSH
Related in: MedlinePlus