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Journal of Bacteriology, January 2008, p. 206-212, Vol. 190, No. 1
0021-9193/08/$08.00+0     doi:10.1128/JB.01227-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Phosphoketolase Pathway Dominates in Lactobacillus reuteri ATCC 55730 Containing Dual Pathways for Glycolysis

Department of Applied Microbiology, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden,¹ Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4,² Department of Microbiology, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden³

Received 30 July 2007/ Accepted 8 October 2007

Metabolic flux analysis indicated that the heterofermentative Lactobacillus reuteri strain ATCC 55730 uses both the Embden-Meyerhof pathway (EMP) and phosphoketolase pathway (PKP) when glucose or sucrose is converted into the three-carbon intermediate stage of glycolysis. In all cases studied, the main flux is through the PKP, while the EMP is used as a shunt. In the exponential growth phase, 70%, 73%, and 84% of the flux goes through the PKP in cells metabolizing (i) glucose plus fructose, (ii) glucose alone, and (iii) sucrose alone, respectively. Analysis of the genome of L. reuteri ATCC 55730 confirmed the presence of the genes for both pathways. Further evidence for the simultaneous operation of two central carbon metabolic pathways was found through the detection of fructose-1,6-bisphosphate aldolase, phosphofructokinase, and phosphoglucoisomerase activities and the presence of phosphorylated EMP and PKP intermediates using in vitro ³¹P NMR. The maximum specific growth rate and biomass yield obtained on glucose were twice as low as on sucrose. This was the result of low ATP levels being present in glucose-metabolizing cells, although the ATP production flux was as high as in sucrose-metabolizing cells due to a twofold increase of enzyme activities in both glycolytic pathways. Growth performance on glucose could be improved by adding fructose as an external electron acceptor, suggesting that the observed behavior is due to a redox imbalance causing energy starvation.

Published ahead of print on 26 October 2007.