Expression of Genes Encoding F 1 -ATPase Results in Uncoupling of Glycolysis from Biomass Production in Lactococcus lactis (original) (raw)
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Biotechnology and Applied Biochemistry, 2008
Steady state cultivation and multidimensional data analysis (metabolic fluxes, absolute proteome, and transcriptome) are used to identify parameters that control the increase in biomass yield of Lactococcus lactis from 0.10 to 0.12 C-mol C-mol 21 with an increase in specific growth rate by 5 times from 0.1 to 0.5 h 21 . Reorganization of amino acid consumption was expressed by the inactivation of the arginine deiminase pathway at a specific growth rate of 0.35 h 21 followed by reduced over-consumption of pyruvate directed amino acids (asparagine, serine, threonine, alanine and cysteine) until almost all consumed amino acids were used only for protein synthesis at maximal specific growth rate. This balanced growth was characterized by a high glycolytic flux carrying up to 87% of the carbon flow and only amino acids that relate to nucleotide synthesis (glutamine, serine and asparagine) were consumed in higher amounts than required for cellular protein synthesis. Changes in the proteome were minor (mainly increase in the translation apparatus). Instead, the apparent catalytic activities of enzymes and ribosomes increased by 3.5 times (0.1 vs 0.5 h 21 ). The apparent catalytic activities of glycolytic enzymes and ribosomal proteins were seen to follow this regulation pattern while those of enzymes involved in nucleotide metabolism increased more than the specific growth rate (over 5.5 times). Nucleotide synthesis formed the most abundant biomonomer synthetic pathway in the cells with an expenditure of 6% from the total ATP required for biosynthesis. Due to the increase in apparent catalytic activity, ribosome translation was more efficient at higher growth rates as evidenced by a decrease of protein to mRNA ratios. All these effects resulted in a 30% decrease of calculated ATP spilling (0.1 vs 0.5 h 21 ). Our results show that bioprocesses can be made more efficient (using a balanced metabolism) by varying the growth conditions.
Molecular Physiology of Sugar Catabolism in Lactococcus lactis IL1403
Journal of Bacteriology, 2001
The metabolic characteristics of Lactococcus lactis IL1403 were examined on two different growth media with respect to the physiological response to two sugars, glucose and galactose. Analysis of specific metabolic rates indicated that despite significant variations in the rates of both growth and sugar consumption, homolactic fermentation was maintained for all cultures due to the low concentration of either pyruvate-formate lyase or alcohol dehydrogenase. When the ionophore monensin was added to the medium, flux through glycolysis was not increased, suggesting a catabolic flux limitation, which, with the low intracellular concentrations of glycolytic intermediates and high in vivo glycolytic enzyme capacities, may be at the level of sugar transport. To assess transcription, a novel DNA macroarray technology employed RNA labeled in vitro with digoxigenin and detection of hybrids with an alkaline phosphatase-antidigoxigenin conjugate. This method showed that several genes of glycolysis were expressed to higher levels on glucose and that the genes of the mixed-acid pathway were expressed to higher levels on galactose. When rates of enzyme synthesis are compared to transcript concentrations, it can be deduced that some translational regulation occurs with threefold-higher translational efficiency in cells grown on glucose.
Molecular Biology Reports, 2002
Using molecular genetics we have introduced uncoupled ATPase activity in two different bacterial species, Escherichia coli and Lactococcus lactis, and determined the elasticities of the growth rate and glycolytic flux towards the intracellular [ATP]/[ADP] ratio. During balanced growth in batch cultures of E. coli the ATP demand was found to have almost full control on the glycolytic flux (FCC=0.96) and the flux could be stimulated by 70%. In contrast to this, in L. lactis the control by ATP demand on the glycolytic flux was close to zero. However, when we used non-growing cells of L. lactis (which have a low glycolytic flux) the ATP demand had a high flux control and the flux could be stimulated more than two fold. We suggest that the extent to which ATP demand controls the glycolytic flux depends on how much excess capacity of glycolysis is present in the cells.
Journal of bacteriology, 1997
During batch growth of Lactococcus lactis subsp. lactis NCDO 2118 on various sugars, the shift from homolactic to mixed-acid metabolism was directly dependent on the sugar consumption rate. This orientation of pyruvate metabolism was related to the flux-controlling activity of glyceraldehyde-3-phosphate dehydrogenase under conditions of high glycolytic flux on glucose due to the NADH/NAD+ ratio. The flux limitation at the level of glyceraldehyde-3-phosphate dehydrogenase led to an increase in the pool concentrations of both glyceraldehyde-3-phosphate and dihydroxyacetone-phosphate and inhibition of pyruvate formate lyase activity. Under such conditions, metabolism was homolactic. Lactose and to a lesser extent galactose supported less rapid growth, with a diminished flux through glycolysis, and a lower NADH/NAD+ ratio. Under such conditions, the major pathway bottleneck was most probably at the level of sugar transport rather than glyceraldehyde-3-phosphate dehydrogenase. Consequent...
The Pool of ADP and ATP Regulates Anaerobic Product Formation in Resting Cells of Lactococcus lactis
Applied and Environmental Microbiology, 2004
Lactococcus lactis grows homofermentatively on glucose, while its growth on maltose under anaerobic conditions results in mixed acid product formation in which formate, acetate, and ethanol are formed in addition to lactate. Maltose was used as a carbon source to study mixed acid product formation as a function of the growth rate. In batch and nitrogen-limited chemostat cultures mixed acid product formation was shown to be linked to the growth rate, and homolactic fermentation occurred only in resting cells. Two of the four lactococcal strains investigated with maltose, L. lactis 65.1 and MG1363, showed more pronounced mixed acid product formation during growth than L. lactis ATCC 19435 or IL-1403. In resting cell experiments all four strains exhibited homolactic fermentation. In resting cells the intracellular concentrations of ADP, ATP, and fructose 1,6-bisphosphate were increased and the concentration of P i was decreased compared with the concentrations in growing cells. Addition of an ionophore (monensin or valinomycin) to resting cultures of L. lactis 65.1 induced mixed acid product formation concomitant with decreases in the ADP, ATP, and fructose 1,6-bisphosphate concentrations. ADP and ATP were shown to inhibit glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, and alcohol dehydrogenase in vitro. Alcohol dehydrogenase was the most sensitive enzyme and was totally inhibited at an adenine nucleotide concentration of 16 mM, which is close to the sum of the intracellular concentrations of ADP and ATP of resting cells. This inhibition of alcohol dehydrogenase might be partially responsible for the homolactic behavior of resting cells. A hypothesis regarding the level of the ATP-ADP pool as a regulating mechanism for the glycolytic flux and product formation in L. lactis is discussed.
Is the Glycolytic Flux in Lactococcus lactis Primarily Controlled by the Redox Charge?
The involvement of nicotinamide adenine nucleotides (NAD ؉ , NADH) in the regulation of glycolysis in Lactococcus lactis was investigated by using 13 C and 31 P NMR to monitor in vivo the kinetics of the pools of NAD ؉ , NADH, ATP, inorganic phosphate (P i ), glycolytic intermediates, and end products derived from a pulse of glucose. Nicotinic acid specifically labeled on carbon 5 was synthesized and used in the growth medium as a precursor of pyridine nucleotides to allow for in vivo detection of 13 C-labeled NAD ؉ and NADH. The capacity of L. lactis MG1363 to regenerate NAD ؉ was manipulated either by turning on NADH oxidase activity or by knocking out the gene encoding lactate dehydrogenase (LDH). An LDH ؊ deficient strain was constructed by double crossover. Upon supply of glucose, NAD ؉ was constant and maximal (ϳ5 mM) in the parent strain (MG1363) but decreased abruptly in the LDH ؊ strain both under aerobic and anaerobic conditions. NADH in MG1363 was always below the detection limit as long as glucose was available. The rate of glucose consumption under anaerobic conditions was 7-fold lower in the LDH ؊ strain and NADH reached high levels (2.5 mM), reflecting severe limitation in regenerating NAD ؉ . However, under aerobic conditions the glycolytic flux was nearly as high as in MG1363 despite the accumulation of NADH up to 1.5 mM. Glyceraldehyde-3-phosphate dehydrogenase was able to support a high flux even in the presence of NADH concentrations much higher than those of the parent strain. We interpret the data as showing that the glycolytic flux in wild type L. lactis is not primarily controlled at the level of glyceraldehyde-3-phosphate dehydrogenase by NADH. The ATP/ADP/P i content could play an important role.
Catalytic Properties of the Membrane-Bound ATPase of Anaerobic Bacterium Lactobacillus casei
Research Article, 1988
Membrane fragments of Lactobacillus casei possess Mg2+-stimulated DCCD-sensitive ATPase activity (0.3-0.5 (µmol/min per mg of protein) with K m for ATP of about 1 mM. Mg2+-stimulated ATPase activity of membranes is maximal at pH 6.0-6.2 and decreases sharply when pH rises to 6.7. Mg2+-ATPase activity of membranes is stimulated by sulfite and octylglucoside. In the presence of ATP-regenerating system, ATPase activity of membranes decreases in the course of ATP hydrolysis. This decrease is prevented by sulfite. Azide has no effect on the initial rate of ATP hydrolysis but enhances markedly the decrease of enzyme activity during ATP hydrolysis. Half-maximal inhibition of Mg2+-stimulated ATPase activity is caused by 15 µM azide. The inhibitory action of azide is reversed by sulfite. It follows from the results presented that there is an ATPase of FoF1-type in the membranes of L. casei.
Regulation of glycolysis in Lactococcus lactis: an unfinished systems biological case study
Iee Proceedings - Systems Biology, 2006
The unexpectedly long, and still unfinished, path towards a reliable mathematical model of glycolysis and its regulation in Lactococcus lactis is described. The model of this comparatively simple pathway was to be deduced from in vivo nuclear magnetic resonance time-series measurements of the key glycolytic metabolites. As to be expected from any nonlinear inverse problem, computational challenges were encountered in the numerical determination of parameter values of the model. Some of these were successfully solved, whereas others are still awaiting improved techniques of analysis. In addition, rethinking of the model formulation became necessary, because some generally accepted assumptions during model design are not necessarily valid for in vivo models. Examples include precursor -product relationships and the homogeneity of cells and their responses. Finally, it turned out to be useful to model only some of the metabolites, while using time courses of ubiquitous compounds such as adenosine triphosphate, inorganic phosphate, nicotinamide adenine dinucleotide (oxidised) and nicotinamide adenine dinucleotide (reduced) as unmodelled input functions. With respect to our specific application, the modelling process has come a long way, but it is not yet completed. Nonetheless, the model analysis has led to interesting insights into the design of the pathway and into the principles that govern its operation. Specifically, the widely observed feedforward activation of pyruvate kinase by fructose 1,6-bisphosphate is shown to provide a crucial mechanism for positioning the starving organism in a holding pattern that allows immediate uptake of glucose, as soon as it becomes available.