HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Desvaux, M. Articles by Petitdemange, H. Search for Related Content PubMed PubMed Citation Articles by Desvaux, M. Articles by Petitdemange, H. Agricola Articles by Desvaux, M. Articles by Petitdemange, H.

Metabolic flux in cellulose batch and cellulose-fed continuous cultures of Clostridium cellulolyticum in response to acidic environment

Laboratoire de Biochimie des Bactéries Gram +, Domaine Scientifique Victor Grignard, Université Henri Poincaré, Faculté des Sciences, BP 239, 54506 Vanduvre-lès-Nancy Cédex, France¹

Author for correspondence: Henri Petitdemange. Tel: +33 3 83 91 20 53. Fax: +33 3 83 91 25 50. e-mail: hpetitde{at}lcb.uhp-nancy.fr

Clostridium cellulolyticum, a nonruminal cellulolytic mesophilic bacterium, was grown in batch and continuous cultures on cellulose using a chemically defined medium. In batch culture with unregulated pH, less cellulose degradation and higher accumulation of soluble glucides were obtained compared to a culture with the pH controlled at 7·2. The gain in cellulose degradation achieved with pH control was offset by catabolite production rather than soluble sugar accumulation. The pH-controlled condition improved biomass, ethanol and acetate production, whereas maximum lactate and extracellular pyruvate concentrations were lower than in the non-pH-controlled condition. In a cellulose-fed chemostat at constant dilution rate and pH values ranging from 7·4 to 6·2, maximum cell density was obtained at pH 7·0. Environmental acidification chiefly influenced biomass formation, since at pH 6·4 the dry weight of cells was more than fourfold lower compared to that at pH 7·0, whereas the specific rate of cellulose assimilation decreased only from 11·74 to 10·13 milliequivalents of carbon (g cells)^-1 h^-1. The molar growth yield and the energetic growth yield did not decline as pH was lowered, and an abrupt transition to washout was observed. Decreasing the pH induced a shift from an acetate-ethanol fermentation to a lactate-ethanol fermentation. The acetate/ethanol ratio decreased as the pH declined, reaching close to 1 at pH 6·4. Whatever the pH conditions, lactate dehydrogenase was always greatly in excess. As pH decreased, both the biosynthesis and the catabolic efficiency of the pyruvate-ferredoxin oxidoreductase declined, as indicated by the ratio of the specific enzyme activity to the specific metabolic rate, which fell from 9·8 to 1·8. Thus a change of only 1 pH unit induced considerable metabolic change and ended by washout at around pH 6·2. C. cellulolyticum appeared to be similar to rumen cellulolytic bacteria in its sensitivity to acidic conditions. Apparently, the cellulolytic anaerobes studied thus far do not thrive when the pH drops below 6·0, suggesting that they evolved in environments where acid tolerance was not required for successful competition with other microbes.

Keywords: cellulolytic bacteria, flux analysis, environmental pH, cellulose degradation, chemostat

Abbreviations: AADH, acetaldehyde dehydrogenase; AK, acetate kinase; ADH, alcohol dehydrogenase; ATP-Eff, efficiency of ATP generation; Fd, ferredoxin; G1P, glucose 1-phosphate; G6P, glucose 6-phosphate; LDH, lactate dehydrogenase; meq C, milliequivalent of carbon; PFO, pyruvate–ferredoxin oxidoreductase; PTA, phosphotransacetylase; R, ratio of specific enzyme activity to metabolic flux

This article has been cited by other articles:

				C.-J. Chou, K. R. Shockley, S. B. Conners, D. L. Lewis, D. A. Comfort, M. W. W. Adams, and R. M. Kelly Impact of Substrate Glycoside Linkage and Elemental Sulfur on Bioenergetics of and Hydrogen Production by the Hyperthermophilic Archaeon Pyrococcus furiosus Appl. Envir. Microbiol., November 1, 2007; 73(21): 6842 - 6853. [Abstract] [Full Text] [PDF]

				M. Desvaux and H. Petitdemange Flux Analysis of the Metabolism of Clostridium cellulolyticum Grown in Cellulose-Fed Continuous Culture on a Chemically Defined Medium under Ammonium-Limited Conditions Appl. Envir. Microbiol., September 1, 2001; 67(9): 3846 - 3851. [Abstract] [Full Text] [PDF]