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Production of L-carnitine by secondary metabolism of bacteria.

Bernal V, Sevilla A, Cánovas M, Iborra JL - Microb. Cell Fact. (2007)

Bottom Line: The use of different cell environments, such as growing, resting, permeabilized, dried, osmotically stressed, freely suspended and immobilized cells, to maintain enzymes sufficiently active for L-carnitine production is discussed in the text.Moreover, the combined application of both bioprocess and metabolic engineering has allowed a deeper understanding of the main factors controlling the production process, such as energy depletion and the alteration of the acetyl-CoA/CoA ratio which are coupled to the end of the biotransformation.Furthermore, the profiles of key central metabolic activities such as the TCA cycle, the glyoxylate shunt and the acetate metabolism are seen to be closely interrelated and affect the biotransformation efficiency.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology B and Immunology, Campus of Espinardo, University of Murcia, E-30100, Spain. jliborra@um.es.

ABSTRACT
The increasing commercial demand for L-carnitine has led to a multiplication of efforts to improve its production with bacteria. The use of different cell environments, such as growing, resting, permeabilized, dried, osmotically stressed, freely suspended and immobilized cells, to maintain enzymes sufficiently active for L-carnitine production is discussed in the text. The different cell states of enterobacteria, such as Escherichia coli and Proteus sp., which can be used to produce L-carnitine from crotonobetaine or D-carnitine as substrate, are analyzed. Moreover, the combined application of both bioprocess and metabolic engineering has allowed a deeper understanding of the main factors controlling the production process, such as energy depletion and the alteration of the acetyl-CoA/CoA ratio which are coupled to the end of the biotransformation. Furthermore, the profiles of key central metabolic activities such as the TCA cycle, the glyoxylate shunt and the acetate metabolism are seen to be closely interrelated and affect the biotransformation efficiency. Although genetically modified strains have been obtained, new strain improvement strategies are still needed, especially in Escherichia coli as a model organism for molecular biology studies. This review aims to summarize and update the state of the art in L-carnitine production using E. coli and Proteus sp, emphasizing the importance of proper reactor design and operation strategies, together with metabolic engineering aspects and the need for feed-back between wet and in silico work to optimize this biotransformation.

No MeSH data available.


Related in: MedlinePlus

L-carnitine transport systems in E. coli strains. A) Main characteristics of L-carnitine transporters: CaiT: carnitine/crotonobetaine/γ-butyrobetaine antiporter [20]; ProU and ProP, osmotic stress related transporters [6,69]. B) Effect of permeabilizers on cell envelope and outer membrane Adapted from [76].
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Figure 2: L-carnitine transport systems in E. coli strains. A) Main characteristics of L-carnitine transporters: CaiT: carnitine/crotonobetaine/γ-butyrobetaine antiporter [20]; ProU and ProP, osmotic stress related transporters [6,69]. B) Effect of permeabilizers on cell envelope and outer membrane Adapted from [76].

Mentions: Besides, the molecular composition of bacterial membrane can be engineered in order to increase the occurrence of membrane transporters. L-carnitine, as well as other betaines, are osmoprotectants, which means that bacteria can accumulate them intracellularly in order to allow them to cope with high extracellular amounts of osmotically active compounds [6,35,69,70]. Thus, cells were subjected to salt stress conditions in order to induce the expression of the betaine transporters involved in osmoprotection, with the aim of tuning up cellular L-carnitine uptake rates [6,71] (Fig. 2A). Finally, the application of molecular biology techniques allows specific targeting of the overexpression of selected genes, such as that of the antiporter CaiT [72].


Production of L-carnitine by secondary metabolism of bacteria.

Bernal V, Sevilla A, Cánovas M, Iborra JL - Microb. Cell Fact. (2007)

L-carnitine transport systems in E. coli strains. A) Main characteristics of L-carnitine transporters: CaiT: carnitine/crotonobetaine/γ-butyrobetaine antiporter [20]; ProU and ProP, osmotic stress related transporters [6,69]. B) Effect of permeabilizers on cell envelope and outer membrane Adapted from [76].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2131755&req=5

Figure 2: L-carnitine transport systems in E. coli strains. A) Main characteristics of L-carnitine transporters: CaiT: carnitine/crotonobetaine/γ-butyrobetaine antiporter [20]; ProU and ProP, osmotic stress related transporters [6,69]. B) Effect of permeabilizers on cell envelope and outer membrane Adapted from [76].
Mentions: Besides, the molecular composition of bacterial membrane can be engineered in order to increase the occurrence of membrane transporters. L-carnitine, as well as other betaines, are osmoprotectants, which means that bacteria can accumulate them intracellularly in order to allow them to cope with high extracellular amounts of osmotically active compounds [6,35,69,70]. Thus, cells were subjected to salt stress conditions in order to induce the expression of the betaine transporters involved in osmoprotection, with the aim of tuning up cellular L-carnitine uptake rates [6,71] (Fig. 2A). Finally, the application of molecular biology techniques allows specific targeting of the overexpression of selected genes, such as that of the antiporter CaiT [72].

Bottom Line: The use of different cell environments, such as growing, resting, permeabilized, dried, osmotically stressed, freely suspended and immobilized cells, to maintain enzymes sufficiently active for L-carnitine production is discussed in the text.Moreover, the combined application of both bioprocess and metabolic engineering has allowed a deeper understanding of the main factors controlling the production process, such as energy depletion and the alteration of the acetyl-CoA/CoA ratio which are coupled to the end of the biotransformation.Furthermore, the profiles of key central metabolic activities such as the TCA cycle, the glyoxylate shunt and the acetate metabolism are seen to be closely interrelated and affect the biotransformation efficiency.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology B and Immunology, Campus of Espinardo, University of Murcia, E-30100, Spain. jliborra@um.es.

ABSTRACT
The increasing commercial demand for L-carnitine has led to a multiplication of efforts to improve its production with bacteria. The use of different cell environments, such as growing, resting, permeabilized, dried, osmotically stressed, freely suspended and immobilized cells, to maintain enzymes sufficiently active for L-carnitine production is discussed in the text. The different cell states of enterobacteria, such as Escherichia coli and Proteus sp., which can be used to produce L-carnitine from crotonobetaine or D-carnitine as substrate, are analyzed. Moreover, the combined application of both bioprocess and metabolic engineering has allowed a deeper understanding of the main factors controlling the production process, such as energy depletion and the alteration of the acetyl-CoA/CoA ratio which are coupled to the end of the biotransformation. Furthermore, the profiles of key central metabolic activities such as the TCA cycle, the glyoxylate shunt and the acetate metabolism are seen to be closely interrelated and affect the biotransformation efficiency. Although genetically modified strains have been obtained, new strain improvement strategies are still needed, especially in Escherichia coli as a model organism for molecular biology studies. This review aims to summarize and update the state of the art in L-carnitine production using E. coli and Proteus sp, emphasizing the importance of proper reactor design and operation strategies, together with metabolic engineering aspects and the need for feed-back between wet and in silico work to optimize this biotransformation.

No MeSH data available.


Related in: MedlinePlus