PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
Logo of biotbiofuelBioMed CentralBiomed Central Web Sitesearchsubmit a manuscriptregisterthis articleBiotechnology for Biofuels
 
Biotechnol Biofuels. 2012; 5: 34.
Published online May 15, 2012. doi:  10.1186/1754-6834-5-34
PMCID: PMC3462113
Dynamic metabolomics differentiates between carbon and energy starvation in recombinant Saccharomyces cerevisiae fermenting xylose
Basti Bergdahl,corresponding author1 Dominik Heer,2 Uwe Sauer,2 Bärbel Hahn-Hägerdal,1 and Ed WJ van Niel1
1Applied Microbiology, Lund University, PO Box 124, SE-221 00, Lund, Sweden
2ETH Zurich, Zurich, 8093, Switzerland
corresponding authorCorresponding author.
Basti Bergdahl: basti.bergdahl/at/tmb.lth.se; Dominik Heer: heer/at/imsb.biol.ethz.ch; Uwe Sauer: sauer/at/imsb.biol.ethz.ch; Bärbel Hahn-Hägerdal: barbel.hahn-hagerdal/at/tmb.lth.se; Ed WJ van Niel: ed.van_niel/at/tmb.lth.se
Received November 15, 2011; Accepted April 23, 2012.
Abstract
Background
The concerted effects of changes in gene expression due to changes in the environment are ultimately reflected in the metabolome. Dynamics of metabolite concentrations under a certain condition can therefore give a description of the cellular state with a high degree of functional information. We used this potential to evaluate the metabolic status of two recombinant strains of Saccharomyces cerevisiae during anaerobic batch fermentation of a glucose/xylose mixture. Two isogenic strains were studied, differing only in the pathways used for xylose assimilation: the oxidoreductive pathway with xylose reductase (XR) and xylitol dehydrogenase (XDH) or the isomerization pathway with xylose isomerase (XI). The isogenic relationship between the two strains ascertains that the observed responses are a result of the particular xylose pathway and not due to unknown changes in regulatory systems. An increased understanding of the physiological state of these strains is important for further development of efficient pentose-utilizing strains for bioethanol production.
Results
Using LC-MS/MS we determined the dynamics in the concentrations of intracellular metabolites in central carbon metabolism, nine amino acids, the purine nucleotides and redox cofactors. The general response to the transition from glucose to xylose was increased concentrations of amino acids and TCA-cycle intermediates, and decreased concentrations of sugar phosphates and redox cofactors. The two strains investigated had significantly different uptake rates of xylose which led to an enhanced response in the XI-strain. Despite the difference in xylose uptake rate, the adenylate energy charge remained high and stable around 0.8 in both strains. In contrast to the adenylate pool, large changes were observed in the guanylate pool.
Conclusions
The low uptake of xylose by the XI-strain led to several distinguished responses: depletion of key metabolites in glycolysis and NADPH, a reduced GTP/GDP ratio and accumulation of PEP and aromatic amino acids. These changes are strong indicators of carbon starvation. The XR/XDH-strain displayed few such traits. The coexistence of these traits and a stable adenylate charge indicates that xylose supplies energy to the cells but does not suppress a response similar to carbon starvation. Particular signals may play a role in the latter, of which the GTP/GMP ratio could be a candidate as it decreased significantly in both strains.
Keywords: Metabolomics, Yeast metabolism, Xylose fermentation, Metabolic status, Starvation, Bioethanol
Articles from Biotechnology for Biofuels are provided here courtesy of
BioMed Central