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Appl. Environ. Microbiol. doi:10.1128/AEM.02914-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Kinetics and metabolism of Bifidobacterium adolescentis MB 239 growing on glucose, galactose, lactose, and galacto-oligosaccharides

Department of Pharmaceutical Sciences, University of Bologna, Italy; Department of Chemistry, University of Ferrara, Italy; Department of Chemistry, University of Modena and Reggio Emilia, Italy

^* To whom correspondence should be addressed. Email: rossi.maddalena{at}unimore.it.

	Abstract

The kinetics and the metabolism of Bifidobacterium adolescentis MB 239 growing on galacto-oligosaccharides (GOS), lactose, galactose, and glucose were investigated. An unstructured unsegregated model for growth in batch cultures was developed and kinetic parameters were calculated with a recursive algorithm. The growth rate and cellular yield were the highest on galactose, followed by lactose and GOS, and were the lowest on glucose. Lactate, acetate and ethanol yields allowed the calculation of carbon fluxes toward fermentation products. Similar distribution between 2- and 3-carbon products was observed on all the carbohydrates (55 and 45%, respectively), but ethanol yield was different on glucose, GOS, lactose, and galactose, in decreasing order of production. Based on the stoichiometry of the fructose 6-phosphate shunt and on the carbon distribution among the products, ATP yield was calculated. The highest was obtained on galactose, while it was 5, 8, and 25% lower on lactose, GOS, and glucose, respectively. Therefore, a correspondence among ethanol production, low ATP yields, and low biomass production was established demonstrating that carbohydrate preferences may result from different distribution of carbon fluxes through the fermentative pathway. During the fermentation of a GOS mixture, substrate selectivity, based on the degree of polymerization was exhibited, since lactose and the trisaccharide were first to be consumed, while a delay was observed until longer oligosaccharides were utilized. Throughout the growth on both lactose and GOS, galactose accumulated in the cultural broth, suggesting that -(1-4) galactosides can be hydrolysed before they are taken up.

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