Document Detail

Salt stress effects on the central and carnitine metabolisms of Escherichia coli.
MedLine Citation:
PMID:  16894634     Owner:  NLM     Status:  MEDLINE    
The aim was to understand how interaction of the central carbon and the secondary carnitine metabolisms is affected under salt stress and its effect on the production of L-carnitine by Escherichia coli. The biotransformation of crotonobetaine into L-carnitine by resting cells of E. coli O44 K74 was improved by salt stress, a yield of nearly twofold that for the control being obtained with 0.5 M NaCl. Crotonobetaine and the L-carnitine formed acted as an osmoprotectant during cell growth and biotransformation in the presence of NaCl. The enzyme activities involved in the biotransformation process (crotonobetaine hydration reaction and crotonobetaine reduction reaction), in the synthesis of acetyl-CoA/acetate (pyruvate dehydrogenase, acetyl-CoA synthetase [ACS] and ATP/acetate phosphotransferase) and in the distribution of metabolites for the tricarboxylic acid cycle (isocitrate dehydrogenase [ICDH]) and glyoxylate shunt (isocitrate lyase [ICL]) were followed in batch with resting cells both in the presence and absence of NaCl and in perturbation experiments performed on growing cells in a high density cell recycle membrane reactor. Further, the levels of carnitine, crotonobetaine, gamma-butyrobetaine and ATP and the NADH/NAD(+) ratio were measured in order to know how the metabolic state was modified and coenzyme pools redistributed as a result of NaCl's effect on the energy content of the cell. The results provided the first experimental evidence of the important role played by salt stress during resting and growing cell biotransformation (0.5 M NaCl increased the L-carnitine production in nearly 85%), and the need for high levels of ATP to maintain metabolite transport and biotransformation. Moreover, the main metabolic pathways and carbon flow operating during cell biotransformation was that controlled by the ICDH/ICL ratio, which decreased from 8.0 to 2.5, and the phosphotransferase/ACS ratio, which increased from 2.1 to 5.2, after a NaCl pulse fivefold the steady-state level. Resting E. coli cells were seen to be made up of heterogeneous populations consisting of several types of subpopulation (intact, depolarized, and permeabilized cells) differing in viability and metabolic activity as biotransformation run-time and the NaCl concentration increased. The results are discussed in relation with the general stress response of E. coli, which alters the NADH/NAD(+) ratio, ATP content, and central carbon enzyme activities.
M Cánovas; V Bernal; A Sevilla; T Torroglosa; J L Iborra
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Biotechnology and bioengineering     Volume:  96     ISSN:  0006-3592     ISO Abbreviation:  Biotechnol. Bioeng.     Publication Date:  2007 Mar 
Date Detail:
Created Date:  2007-02-01     Completed Date:  2007-03-22     Revised Date:  2013-12-10    
Medline Journal Info:
Nlm Unique ID:  7502021     Medline TA:  Biotechnol Bioeng     Country:  United States    
Other Details:
Languages:  eng     Pagination:  722-37     Citation Subset:  IM    
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MeSH Terms
Betaine / analogs & derivatives,  metabolism
Biotransformation / physiology
Carbon / metabolism*
Carnitine / metabolism*
Escherichia coli / enzymology,  metabolism*
Metabolic Networks and Pathways*
Osmotic Pressure
Sodium Chloride / pharmacology*
Reg. No./Substance:
3SCV180C9W/Betaine; 541-15-1/Carnitine; 7440-44-0/Carbon; 7647-14-5/Sodium Chloride; 927-89-9/crotonic acid betaine
Erratum In:
Biotechnol Bioeng. 2013 Dec;110(12):3275
Note: Torroglosa, T [added]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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