NDLI: Kinetics and Metabolism of Cellulose Degradation at High Substrate Concentrations in Steady-State Continuous Cultures of Clostridium cellulolyticum on a Chemically Defined Medium

Content Provider	PubMed Central
Author	Desvaux, Mickaël Guedon, Emmanuel Henri, Petitdemange
Copyright Year	2001
Abstract	The hydrolysis and fermentation of insoluble cellulose were investigated using continuous cultures of Clostridium cellulolyticum with increasing amounts of carbon substrate. At a dilution rate (D) of 0.048 h−1, biomass formation increased proportionately to the cellulose concentration provided by the feed reservoir, but at and above 7.6 g of cellulose liter−1 the cell density at steady state leveled off. The percentage of cellulose degradation declined from 32.3 to 8.3 with 1.9 and 27.0 g of cellulose liter−1, respectively, while cellodextrin accumulation rose and represented up to 4.0% of the original carbon consumed. The shift from cellulose-limited to cellulose-sufficient conditions was accompanied by an increase of both the acetate/ethanol ratio and lactate biosynthesis. A kinetics study of C. cellulolyticum metabolism in cellulose saturation was performed by varying D with 18.1 g of cellulose liter−1. Compared to cellulose limitation (M. Desvaux, E. Guedon, and H. Petitdemange, J. Bacteriol. 183:119–130, 2001), in cellulose-sufficient continuous culture (i) the ATP/ADP, NADH/NAD+, and q NADH produced/q NADH used ratios were higher and were related to a more active catabolism, (ii) the acetate/ethanol ratio increased while the lactate production decreased as D rose, and (iii) the maximum growth yield (Y \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\setlength{\oddsidemargin}{-69pt}\begin{document}\begin{equation}{\mathrm{_{{X/S}}^{max}}}\end{equation}\end{document} ) (40.6 g of biomass per mol of hexose equivalent) and the maximum energetic yield (Y \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy}\usepackage{mathrsfs}\setlength{\oddsidemargin}{-69pt}\begin{document}\begin{equation}{\mathrm{_{ATP}^{max}}}\end{equation}\end{document} ) (19.4 g of biomass per mol of ATP) were lowered. C. cellulolyticum was then able to regulate and optimize carbon metabolism under cellulose-saturated conditions. However, the facts that some catabolized hexose and hence ATP were no longer associated with biomass production with a cellulose excess and that concomitantly lactate production and pyruvate leakage rose suggest the accumulation of an intracellular inhibitory compound(s), which could further explain the establishment of steady-state continuous cultures under conditions of excesses of all nutrients. The following differences were found between growth on cellulose in this study and growth under cellobiose-sufficient conditions (E. Guedon, S. Payot, M. Desvaux, and H. Petitdemange, Biotechnol. Bioeng. 67:327–335, 2000): (i) while with cellobiose, a carbon flow into the cell of as high as 5.14 mmol of hexose equivalent g of cells−1 h−1 could be reached, the maximum entering carbon flow obtained here on cellulose was 2.91 mmol of hexose equivalent g of cells−1 h−1; (ii) while the NADH/NAD+ ratio could reach 1.51 on cellobiose, it was always lower than 1 on cellulose; and (iii) while a high proportion of cellobiose was directed towards exopolysaccharide, extracellular protein, and free amino acid excretions, these overflows were more limited under cellulose-excess conditions. Such differences were related to the carbon consumption rate, which was higher on cellobiose than on cellulose.
Related Links	http://dx.doi.org/10.1128/aem.67.9.3837-3845.2001
Ending Page	3845
Page Count	9
Starting Page	3837
File Format	PDF
ISSN	00992240
e-ISSN	10985336
Journal	Applied and Environmental Microbiology
Issue Number	9
Volume Number	67
Language	English
Publisher	American Society for Microbiology
Publisher Date	2001-09-01
Access Restriction	Open
Rights Holder	American Society for Microbiology
Subject Keyword	Biotechnology Food Science Ecology Applied Microbiology and Biotechnology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Ecology Food Science Applied Microbiology and Biotechnology Biotechnology

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