Phosphoketolase Pathway Research Articles

Systems Analysis Unfolds the Relationship between the Phosphoketolase Pathway and Growth in Aspergillus nidulans

Background Aspergillus nidulans is an important model organism for studies on fundamental eukaryotic cell biology and on industrial processes due to its close relation to A. niger and A. oryzae. Here we identified the gene coding for a novel metabolic pathway in A. nidulans, namely the phosphoketolase pathway, and investigated the role of an increased phosphoketolase activity.Methodology/Principal FindingsOver-expression of the phosphoketolase gene (phk) improved the specific growth rate on xylose, glycerol and ethanol. Transcriptome analysis showed that a total of 1,222 genes were significantly affected by over-expression of the phk, while more than half of the affected genes were carbon source specific. During growth on glucose medium, the transcriptome analysis showed that the response to phk over-expression is targeted to neutralize the effect of the over-expression by regulating the acetate metabolism and initiate a growth dampening response.Conclusions/SignificanceMetabolic flux analysis using 13C-labelled glucose, showed that over-expression of phosphoketolase added flexibility to the central metabolism. Our findings further suggests that A. nidulans is not optimized for growth on xylose, glycerol or ethanol as the sole carbon sources.

Influence of the Metabolism Pathway on Lactic Acid Production from Hemicellulosic Trimming Vine Shoots Hydrolyzates Using Lactobacillus pentosus

Hemicellulosic hydrolyzates from trimming wastes of vine shoots were proposed as a carbon source for lactic acid production by Lactobacillus pentosus CECT-4023T (ATCC-8041). These hydrolyzates are composed mainly of glucose (12.0 g/L), xylose (17.5 g/L) and arabinose (4.3 g/L). Acetic acid, the main subproduct, started to be produced after all of the glucose was completely depleted, showing that the acetic acid coproduction came only from the xylose and arabinose consumption. In the absence of glucose, the L. pentosus pathway shifts from homo to heterofermentative. Thus, L. pentosus can be considered a facultative heterofermentative organism, degrading hexoses (glucose) via the Embden-Meyerhoff-Parnas pathway and pentoses (xylose and arabinose) via the phosphoketolase pathway. Hydrolyzates were vacuum evaporated to increase the initial sugars concentration up to 35.4 g/L of glucose, 52.3 g/L of xylose, and 13.0 g/L of arabinose. Under these conditions the lactic acid concentration reached 46.0 g/L (Q(P) = 0.933 g/L.h, Y(P/S) = 0.78 g/g; Y(P/S) theoretical = 91.7%) and a clear product inhibition was observed. Additional experiments with synthetic sugars, in the absence of inhibitory compounds, indicate that this inhibition must be attributed to the metabolic pathway but not to the inhibitory compounds present in the fermentation broth.

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

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.

Monitoring novel metabolic pathways using metabolomics and machine learning: induction of the phosphoketolase pathway in Aspergillus nidulans cultivations

The physiological phenotype of Aspergillus nidulans was determined under different environmental conditions through the quantification of the intracellular and extracellular metabolite pools and clear evidence of the presence of a novel fungal metabolic pathway, the phosphoketolase pathway, was obtained. Induction of the phosphoketolase pathway resulted after blocking the EMP pathway through the deactivation of glyceraldehyde-3-P dehydrogenase (G3PD). Deactivation of G3PD in cultivations of A. nidulans on glucose and xylose led to a 10-fold decrease in the specific growth rate; however, growth could still be sustained solely through the phosphoketolase pathway. Metabolomics and machine learning tools were successfully used to monitor the alteration caused by the inhibition of G3PD in the metabolism of A. nidulans grown on glucose, xylose, acetate as well as mixtures of glucose or xylose with acetate. This is the first study that demonstrates in vivo that the fungal central carbon metabolism includes an active phosphoketolase pathway.

Comparison of growth-phase-dependent cytosolic proteomes of twoLactobacillus plantarumstrains used in food and feed fermentations

Lactobacillus plantarum is a facultative heterofermentative lactic acid bacterium highly adapted to a wide variety of environments and widely used in food and feed fermentations. Proteomes of two strains of L. plantarum, one isolated from spontaneously fermented cereal-based feed (strain REB1), and the other from white cabbage (strain MLBPL1), were studied to elucidate the strain-specific variation and the physiological changes occurring between the growth (lag, early-exponential, late-exponential and early-stationary) phases of this bacterium when cultivated in a standard rich medium. A total of 231 protein spots were identified by LC-MS/MS. These proteins showed that strain MLBPL1 had more proteins with growth phase-dependent expression than REB1, which possesses a more constant expression profile. The proteins with growth phase-dependent expression in REB1 and MLBPL1 were mainly associated with energy metabolism (glycolysis, phosphoketolase pathway and ribose metabolism), all having preferential expression in the early-exponential phase, confirming the use of different carbohydrates simultaneously. Indication of energy production was also seen in lag and early-stationary phases.

Conversion of aqueous ammonia-treated corn stover to lactic acid by simultaneous saccharification and cofermentation

Treatment of corn stover with aqueous ammonia removes most of the structural lignin, whereas retaining the majority of the carbohydrates in the solids. After treatment, both the cellulose and hemicellulose in corn stover become highly susceptible to enzymatic digestion. In this study, corn stover treated by aqueous ammonia was investigated as the substrate for lactic acid production by simultaneous saccharification and cofermentation (SSCF). A commercial cellulase (Spezyme-CP) and Lactobacillus pentosus American Type Culture Collection (ATCC) 8041 (Spanish Type Culture Collection [CECT]-4023) were used for hydrolysis and fermentation, respectively. In batch SSCF operation, the carbohydrates in the treated corn stover were converted to lactic acid with high yields, the maximum lactic acid yield reaching 92% of the stoichiometric maximum based on total fermentable carbohydrates (glucose, xylose, and arabinose). A small amount of acetic acid was also produced from pentoses through the phosphoketolase pathway. Among the major process variables for batch SSCF, enzyme loading and the amount of yeast extract were found to be the key factors affecting lactic acid production. Further tests on nutrients indicated that corn steep liquor could be substituted for yeast extract as a nitrogen source to achieve the same lactic acid yield. Fed-batch operation of the SSCF was beneficial in raising the concentration of lactic acid to a maximum value of 75.0 g/L.

Calculation of metabolic flow of xylose in Lactococcus lactis

A circuit diagram is proposed on the basis of an analysis of metabolic pathways of lactic acid bacteria, namely, a phosphoketolase pathway and a pentose phosphate/glycolic pathway. An augmented matrix was derived from carbon balances and stoichiometries from the circuit diagram, and solved by Gaussian elimination. Results indicated that 70% of the amount of xylose was metabolized through the pentose phosphate/glycolic pathway and that the yield of lactic acid from xylose ranged from 0.34 to 0.52 (mol/mol), whereas that of pyruvic acid was more than 1.4 (mol/mol).

Variations in the energy metabolism of biotechnologically relevant heterofermentative lactic acid bacteria during growth on sugars and organic acids

Heterofermentative lactic acid bacteria (LAB) such as Leuconostoc, Oenococcus, and Lactobacillus strains ferment pentoses by the phosphoketolase pathway. The extra NAD(P)H, which is produced during growth on hexoses, is transferred to acetyl-CoA, yielding ethanol. Ethanol fermentation represents the limiting step in hexose fermentation, therefore, part of the extra NAD(P)H is used to produce erythritol and glycerol. Fructose, pyruvate, citrate, and O2 can be used in addition as external electron acceptors for NAD(P)H reoxidation. Use of the external acceptors increases the growth rate of the bacteria. The bacteria are also able to ferment organic acids like malate, pyruvate, and citrate. Malolactic fermentation generates a proton potential by substrate transport. Pyruvate fermentation sustains growth by pyruvate disproportionation involving pyruvate dehydrogenase. Citrate is fermented in the presence of an additional electron donor to acetate and lactate. Thus, heterofermentative LAB are able to use a variety of unusual fermentation reactions in addition to classical heterofermentation. Most of the reactions are significant for food biotechnology/microbiology.

Characterization of genes involved in fructose utilization by Lactobacillus fermentum

The genes encoding phosphoglucose isomerase (fruI) and fructokinase (fruK) of Lactobacillus fermentum NRRL-B-1932 were sequenced. They constituted an operon, which is involved in fructose metabolism of this strain by channeling intracellular fructose into the phosphoketolase pathway. A third open reading frame, unkR, upstream of the operon was identified as homologous to genes of LacI/GalR family repressors. The UnkR repressor's role in transcriptional control of the fruIK operon could, however, not be established by electrophoretic mobility shift assay (EMSA) analysis. Sequence analysis revealed two putative catabolite responsive elements (cre) in the promoter region of fruIK suggesting that the fruIK operon is under negative regulatory control by carbon catabolite repression. Expression and enzyme activity data were compatible with the assumption that the fruIK operon is repressed by glucose. No sugar specific phosphoenolpyruvate sugar transferase system activity for the transport of fructose, glucose, sucrose or mannose could be detected in L. fermentum NRRL-B-1932 cells, which suggest that fructose is taken up by a permease system.

A Proteome Reference Map and Proteomic Analysis of Bifidobacterium longum NCC2705

A comprehensive proteomic study was carried out to identify and characterize proteins expressed by Bifidobacterium longum NCC2705. A total of 708 spots representing 369 protein entries were identified by MALDI-TOF-MS and/or ESI-MS/MS. Isoelectric point values estimated by gel electrophoresis matched closely with their predicted ones, although some discrepancies exist suggesting that post-translational protein modifications might be common in B. longum. The identified proteins represent 21.4% of the predicted 1727 ORFs in the genome and correspond to 30% of the predicted proteome. Moreover 95 hypothetical proteins were experimentally identified. This is the first compilation of a proteomic reference map for the important probiotic organism B. longum NCC2705. The study aimed to define a number of cellular pathways related to important physiological processes at the proteomic level. Proteomic comparison of glucose- and fructose-grown cells revealed that fructose and glucose are catabolized via the same degradation pathway. Interestingly the sugar-binding protein specific to fructose (BL0033) and Frk showed higher levels of expression in cells grown on fructose than on glucose as determined by semiquantitative RT-PCR. BL0033 time course and concentration experiments showed that the induction time and fructose concentration correlates to increased expression of BL0033. At the same time, an ABC (ATP-binding cassette) transporter ATP-binding protein (BL0034) was slightly up-regulated in cells grown on fructose compared with glucose. All of the above results suggest that the uptake of fructose into the cell may be conducted by a specific transport system in which BL0033 might play an important role.

Improved mannitol production by a random mutant of Leuconostoc pseudomesenteroides

A mutant of Leuconostoc pseudomesenteroides ATCC12291 that was unable to grow on fructose was constructed by chemical mutagenesis. The fructose uptake of this mutant, designated as BPT143, was unaltered and allowed fructose still to be converted into mannitol when glucose was present in the growth medium. The mutant grew and consumed fructose faster than the parent strain when grown in a medium containing both glucose and fructose. The specific activity of fructokinase, the enzyme involved in phosphorylation of fructose to fructose-6-phosphate, was decreased to about 10% of that of the parent strain, and resulted in a reduced leakage of fructose into the phosphoketolase (PK) pathway. The yield of mannitol from fructose was improved from 74 to 86 mol%. The increased fructose consumption rate and higher mannitol yield of the mutant also resulted in improvement of volumetric mannitol productivity. In addition, isolation and characterization of the wild type L. pseudomesenteroides fructokinase gene ( fruK) was performed. DNA sequence analysis of the fruK gene region of BPT143 revealed only one silent mutation which does not explain the highly reduced fructokinase activity of the mutant. The genetic characterization of fruK was completed by analyzing the expression, size and 5′ end of fruK transcripts. Expression data with BPT143, revealing absence of fruK transcripts, was in accordance with the reduced fructokinase activity of the mutant.

Bifidobacterium longum requires a fructokinase (Frk; ATP:D-fructose 6-phosphotransferase, EC 2.7.1.4) for fructose catabolism.

Although the ability of Bifidobacterium spp. to grow on fructose as a unique carbon source has been demonstrated, the enzyme(s) needed to incorporate fructose into a catabolic pathway has hitherto not been defined. This work demonstrates that intracellular fructose is metabolized via the fructose-6-P phosphoketolase pathway and suggests that a fructokinase (Frk; EC 2.7.1.4) is the enzyme that is necessary and sufficient for the assimilation of fructose into this catabolic route in Bifidobacterium longum. The B. longum A10C fructokinase-encoding gene (frk) was expressed in Escherichia coli from a pET28 vector with an attached N-terminal histidine tag. The expressed enzyme was purified by affinity chromatography on a Co(2+)-based column, and the pH and temperature optima were determined. A biochemical analysis revealed that Frk displays the same affinity for fructose and ATP (Km(fructose) = 0.739 +/- 0.18 mM and Km(ATP) = 0.756 +/- 0.08 mM), is highly specific for D-fructose, and is inhibited by an excess of ATP (>12 mM). It was also found that frk is inducible by fructose and is subject to glucose-mediated repression. Consequently, this work presents the first characterization at the molecular and biochemical level of a fructokinase from a gram-positive bacterium that is highly specific for D-fructose.

Significance of phosphoglucose isomerase for the shift between heterolactic and mannitol fermentation of fructose by Oenococcus oeni.

The bacterium Oenococcus oeni employs the heterolactic fermentation pathway (products lactate, ethanol, CO(2)) during growth on fructose as a substrate, and the mannitol pathway when using fructose as an electron acceptor. In this study, [U-(13)C]glucose, [U-(13)C]fructose, HPLC, NMR spectroscopy, and enzyme analysis were applied to elucidate the use of both pathways by the hexoses. In the presence of glucose or pyruvate, fructose was metabolized either by the mannitol or the phosphoketolase pathways, respectively. Phosphoglucose isomerase, which is required for channeling fructose into the phosphoketolase pathways, was inhibited by a mixed-type inhibition composed of competitive ( K(i)=180 microM) and uncompetitive ( K'(i)=350 microM) inhibition by 6-phosphogluconate. Erythrose 4-phosphate inhibited phosphoglucose isomerase competitively ( K(i)=1.3 microM) with a low contribution of uncompetitive inhibition ( K'(i)=13 microM). The cellular 6-phosphogluconate content during growth on fructose plus pyruvate (<75 microM) was significantly lower than during growth on fructose alone or fructose plus glucose (550 and 480 microM). We conclude that competitive inhibition of phosphoglucose isomerase by 6-phosphogluconate (and possibly erythrose 4-phosphate) is responsible for exclusion of fructose from the phosphoketolase pathway during growth on fructose plus glucose, but not during growth on fructose plus pyruvate.

Use of the mannitol pathway in fructose fermentation of Oenococcus oeni due to limiting redox regeneration capacity of the ethanol pathway.

The heterolactic bacterium Oenococcus oeni ferments fructose by a mixed heterolactic/mannitol fermentation. For heterolactic fermentation of fructose, the phosphoketolase pathway is used. The excess NAD(P)H from the phosphoketolase pathway is reoxidized by fructose (yielding mannitol). It is shown here that, under conditions of C-limitation or decreased growth rates, fructose can be fermented by heterolactic fermentation yielding nearly stoichiometric amounts of lactate, ethanol and CO(2). Quantitative evaluation of NAD(P)H-producing (phosphoketolase pathway) and -reoxidizing (ethanol, mannitol and erythritol pathways) reactions demonstrated that at high growth rates or in batch cultures the ethanol pathway does not have sufficient capacity for NAD(P)H reoxidation, requiring additional use of the mannitol pathway to maintain the growth rate. In addition, insufficient capacities to reoxidize NAD(P)H causes inhibition of growth, whereas increased NAD(P)H reoxidation by electron acceptors such as pyruvate increases the growth rate.

Complete genome sequence of Lactobacillus plantarum WCFS1.

The 3,308,274-bp sequence of the chromosome of Lactobacillus plantarum strain WCFS1, a single colony isolate of strain NCIMB8826 that was originally isolated from human saliva, has been determined, and contains 3,052 predicted protein-encoding genes. Putative biological functions could be assigned to 2,120 (70%) of the predicted proteins. Consistent with the classification of L. plantarum as a facultative heterofermentative lactic acid bacterium, the genome encodes all enzymes required for the glycolysis and phosphoketolase pathways, all of which appear to belong to the class of potentially highly expressed genes in this organism, as was evident from the codon-adaptation index of individual genes. Moreover, L. plantarum encodes a large pyruvate-dissipating potential, leading to various end-products of fermentation. L. plantarum is a species that is encountered in many different environmental niches, and this flexible and adaptive behavior is reflected by the relatively large number of regulatory and transport functions, including 25 complete PTS sugar transport systems. Moreover, the chromosome encodes >200 extracellular proteins, many of which are predicted to be bound to the cell envelope. A large proportion of the genes encoding sugar transport and utilization, as well as genes encoding extracellular functions, appear to be clustered in a 600-kb region near the origin of replication. Many of these genes display deviation of nucleotide composition, consistent with a foreign origin. These findings suggest that these genes, which provide an important part of the interaction of L. plantarum with its environment, form a lifestyle adaptation region in the chromosome.

Two different pathways for D-xylose metabolism and the effect of xylose concentration on the yield coefficient of L-lactate in mixed-acid fermentation by the lactic acid bacterium Lactococcus lactis IO-1.

In lactic acid bacteria, pentoses are metabolized via the phosphoketolase pathway, which catalyzes the cleavage of D-xylulose-5-phosphate to equimolar amounts of glyceraldehyde 3-phosphate and acetylphosphate. Hence the yield coefficient of lactate from pentose does not exceed 1.0 mol/mol, while that of Lactococcus lactis IO-1(JCM7638) at high D-xylose concentrations often exceeds the theoretical value. This suggests that, in addition to the phosphoketolase pathway, L. lactisIO-1 may possess another metabolic pathway that produces only lactic acid from xylose. In the present study, the metabolism of xylose in L. lactisIO-1 was deduced from the product formation and enzyme activities of L. lactisIO-1 in batch culture and continuous culture. During cultivation with xylose concentrations above ca. 50 g/l, the yield coefficient of L-lactate exceeded 1.0 mol/mol while those of acetate, formate and ethanol were very low. At xylose concentrations less than 5 g/l, acetate, formate and ethanol were produced with yield coefficients of about 1.0 mol/mol, while L-lactate was scarcely produced. In cells grown at high xylose concentrations, a marked decrease in the specific activities of phosphoketolase and pyruvate formate lyase (PFL), and an increase in those of transketolase and transaldolase were observed. These results indicate that in L. lactisIO-1 xylose may be catabolized by two different pathways, the phosphoketolase pathway yielding acetate, formate and ethanol, and the pentose phosphate (PP)/glycolytic pathway which converts xylose to L-lactate only. Furthermore, it was deduced that the change in the xylose concentration in the culture medium shifts xylulose 5-phosphate metabolism between the phosphoketolase pathway and the PP/glycolytic pathway in L. lactisIO-1, and pyruvate metabolism between cleavage to acetyl-CoA and formic acid by PFL and the reduction to L-lactate by lactate dehydrogenase.

Phosphoketolase, a Neglected Enzyme of Microbial Carbohydrate Metabolism

Phosphoketolases are thiamine diphosphate (ThDP) dependent enzymes of the phosphoketolase (PK) pathway of heterofermentative and facultatively homofermentative lactic acid bacteria and of the fructose 6-phosphate shunt of bifidobacteria. PK activity was also measured in protein extracts of other microorganisms including yeasts. The dual substrate xylulose 5-phosphate/fructose 6-phosphate phosphoketolase (Xfp) from the 'probiotic' Bifidobacterium lactis was purified, and its encoding gene (xfp) was cloned and sequenced. Comparisons with public databases revealed an unexpectedly wide spread of more than 30 homologous xfp sequences in the kingdom of the bacteria, but not of the archaea. We assigned amino acid motifs typically found in PKs. Two of them (G-P-G-H-G and E-G-G-E-L-G-Y, respectively) discriminate PKs from transketolases, which have at least one ThDP binding site in common. On the basis of further comparative analyses we conclude that the PK prevalence among diverse organisms is due to longitudinal and not horizontal gene transmission.

2-Amino-3-carboxy-1,4-naphthoquinone affects the end-product profile of bifidobacteria through the mediated oxidation of NAD(P)H.

Glucose metabolism of bifidobacteria in the presence of 2-amino-3-carboxy-1,4-naphthoquinone (ACNQ), a specific growth stimulator for bifidobacteria, and ferricyanide (Fe(CN)(6)(3-)) as an extracellular electron acceptor was examined using resting cells of Bifidobacterium longum and Bifidobacterium breve. NAD(P)H in the cells is oxidized by ACNQ with the aid of diaphorase activity, and reduced ACNQ donates the electron to Fe(CN)(6)(3-). Exogenous oxidation of NADH by the ACNQ/Fe(CN)(6)(3-) system suppresses the endogenous lactate dehydrogenase reaction competitively, which results in the remarkable generation of pyruvate and a decrease in lactate production. In addition, a decrease in acetate generation is also observed in the presence of ACNQ and Fe(CN)(6)(3-). This phenomenon could not be explained in terms of the fructose-6-phosphate phosphoketolase pathway, but suggests rather that glucose is partially metabolized via the hexose monophosphate pathway. This was verified by NADP(+)-induced reduction of Fe(CN)(6)(3-) in cell-free extracts in the presence of ACNQ. Effects of the ACNQ/Fe(CN)(6)(3-) system on anaerobically harvested cells were also examined. Stoichiometric analysis of the metabolites from the pyruvate-formate lyase pathway suggests that exogenous oxidation of NADH is an efficient method to produce ATP in this pathway.

Expression of the xylulose 5-phosphate phosphoketolase gene, xpkA, from Lactobacillus pentosus MD363 is induced by sugars that are fermented via the phosphoketolase pathway and is repressed by glucose mediated by CcpA and the mannose phosphoenolpyruvate phosphotransferase system.

Purification of xylulose 5-phosphate phosphoketolase (XpkA), the central enzyme of the phosphoketolase pathway (PKP) in lactic acid bacteria, and cloning and sequence analysis of the encoding gene, xpkA, from Lactobacillus pentosus MD363 are described. xpkA encodes a 788-amino-acid protein with a calculated mass of 88,705 Da. Expression of xpkA in Escherichia coli led to an increase in XpkA activity, while an xpkA knockout mutant of L. pentosus lost XpkA activity and was not able to grow on energy sources that are fermented via the PKP, indicating that xpkA encodes an enzyme with phosphoketolase activity. A database search revealed that there are high levels of similarity between XpkA and a phosphoketolase from Bifidobacterium lactis and between XpkA and a (putative) protein present in a number of evolutionarily distantly related organisms (up to 54% identical residues). Expression of xpkA in L. pentosus was induced by sugars that are fermented via the PKP and was repressed by glucose mediated by carbon catabolite protein A (CcpA) and by the mannose phosphoenolpyruvate phosphotransferase system. Most of the residues involved in correct binding of the cofactor thiamine pyrophosphate (TPP) that are conserved in transketolase, pyruvate decarboxylase, and pyruvate oxidase were also conserved at a similar position in XpkA, implying that there is a similar TPP-binding fold in XpkA.

Growth and energetics of Leuconostoc mesenteroides NRRL B-1299 during metabolism of various sugars and their consequences for dextransucrase production.

The metabolic and energetic properties of Leuconostoc mesenteroides have been examined with the goal of better understanding the parameters which affect dextransucrase activity and hence allowing the development of strategies for improved dextransucrase production. Glucose and fructose support equivalent specific growth rates (0.6 h-1) under aerobic conditions, but glucose leads to a better biomass yield in anaerobiosis. Both sugars are phosphorylated by specific hexokinases and catabolized through the heterofermentative phosphoketolase pathway. During sucrose-grown cultures, a large fraction of sucrose is converted outside the cell by dextransucrase into dextran and fructose and does not support growth. The other fraction enters the cell, where it is phosphorylated by an inducible sucrose phosphorylase and converted to glucose-6-phosphate (G-6-P) by a constitutive phosphoglucomutase and to heterofermentative products (lactate, acetate, and ethanol). Sucrose supports a higher growth rate (0.98 h-1) than the monosaccharides. When fructose is not consumed simultaneously with G-1-P, the biomass yield relative to ATP is high (16.8 mol of ATP.mol of sucrose-1), and dextransucrase production is directly proportional to growth. However, when the fructose moiety is used, a sink of energy is observed, and dextransucrase production is no longer correlated with growth. As a consequence, fructose catabolism must be avoided to improve the amount of dextransucrase synthesized.