Limiting Amounts Of Glucose Research Articles

Developing a Microbial Consortium for Enhanced Metabolite Production from Simulated Food Waste

Food waste disposal and transportation of commodity chemicals to the point-of-need are substantial challenges in military environments. Here, we propose addressing these challenges via the design of a microbial consortium for the fermentation of food waste to hydrogen. First, we simulated the exchange metabolic fluxes of monocultures and pairwise co-cultures using genome-scale metabolic models on a food waste proxy. We identified that one of the top hydrogen producing co-cultures comprised Clostridium beijerinckii NCIMB 8052 and Yokenella regensburgei ATCC 43003. A consortium of these two strains produced a similar amount of hydrogen gas and increased butyrate compared to the C. beijerinckii monoculture, when grown on an artificial garbage slurry. Increased butyrate production in the consortium can be attributed to cross-feeding of lactate produced by Y. regensburgei. Moreover, exogenous lactate promotes the growth of C. beijerinckii with or without a limited amount of glucose. Increasing the scale of the consortium fermentation proved challenging, as two distinct attempts to scale-up the enhanced butyrate production resulted in different metabolic profiles than observed in smaller scale fermentations. Though the genome-scale metabolic model simulations provided a useful starting point for the design of microbial consortia to generate value-added products from waste materials, further model refinements based on experimental results are required for more robust predictions.

Microbial Production of 1,3-Propanediol by a Newly Isolated <i>Citrobacter freundii</i> Strain CF-5

Microorganisms tolerant to 1, 3-propanediol (1, 3-PDO) were screened out from various environmental samples, and isolate CF-5 was found to produce 2.8 g/L 1, 3-PDO with glycerol as carbon source. Based on 16S rRNA gene sequence analysis, CF-5 was identified as aCitrobacter freundiistrain. The fermentation conditions of strain CF-5 were analyzed. Higher biomass production was obtained in the medium supplemented with limited amount of glucose without repression of conversion efficiency of glycerol to 1, 3-PDO. Under the combined aerobic and oxygen limited incubation conditions, higher yield of 1, 3-PDO was reached. The fed-batch fermentation was performed in a 5 L bioreactor, 1, 3-PDO was found mainly produced in exponential growth phase cells ofC. freundiiCF-5 with the highest productivity 0.63 g/L*h, and the overall yield of 1, 3-PDO fermentation was 11.8 g/L within 36 h fermentation.

Validation of a model of the GAL regulatory system via robustness analysis of its bistability characteristics

BackgroundIn Saccharomyces cerevisiæ, structural bistability generates a bimodal expression of the galactose uptake genes (GAL) when exposed to low and high glucose concentrations. This indicates that yeast cells can decide between using either the limited amount of glucose or growing on galactose under changing environmental conditions. A crucial requirement for any plausible mechanistic model of this system is that it reproduces the robustness of the bistable response observed in vivo against inter-individual parametric variability and fluctuating environmental conditions.ResultsWe show how a control-theoretic analysis of the robustness of a model of the GAL regulatory network may be used to establish the model’s plausibility in characterizing the persistent memory of different carbon sources, without the need for extensive simulations. Chemical Reaction Network Theory is used to establish that the proposed network model is compatible with structural bistability. The robustness of each of the two operative conditions against fluctuations of the species concentrations is demonstrated by studying the Domains of Attraction of the corresponding equilibrium points. Finally, we use a global robustness analysis method based on Semi-Definite Programming to evaluate the modification of the bistable steady states induced by multiple parametric variations throughout bounded regions of the parameter space.ConclusionsOur analysis provides convincing evidence for the robustness, and hence plausibility, of the GAL regulatory network model. The proposed workflow also demonstrates the power of analytical methods from control theory to provide a direct quantitative characterization of the dynamics of multistable biomolecular regulatory systems without recourse to extensive computer simulations.

New Functions for Parts of the Krebs Cycle in Procyclic Trypanosoma brucei, a Cycle Not Operating as a Cycle

We investigated whether substrate availability influences the type of energy metabolism in procyclic Trypanosoma brucei. We show that absence of glycolytic substrates (glucose and glycerol) does not induce a shift from a fermentative metabolism to complete oxidation of substrates. We also show that glucose (and even glycolysis) is not essential for normal functioning and proliferation of pleomorphic procyclic T. brucei cells. Furthermore, absence of glucose did not result in increased degradation of amino acids. Variations in availability of glucose and glycerol did result, however, in adaptations in metabolism in such a way that the glycosome was always in redox balance. We argue that it is likely that, in procyclic cells, phosphoglycerate kinase is located not only in the cytosol, but also inside glycosomes, as otherwise an ATP deficit would occur in this organelle. We demonstrate that procyclic T. brucei uses parts of the Krebs cycle for purposes other than complete degradation of mitochondrial substrates. We suggest that citrate synthase plus pyruvate dehydrogenase and malate dehydrogenase are used to transport acetyl-CoA units from the mitochondrion to the cytosol for the biosynthesis of fatty acids, a process we show to occur in proliferating procyclic cells. The part of the Krebs cycle consisting of alpha-ketoglutarate dehydrogenase and succinyl-CoA synthetase was used for the degradation of proline and glutamate to succinate. We also demonstrate that the subsequent enzymes of the Krebs cycle, succinate dehydrogenase and fumarase, are most likely used for conversion of succinate into malate, which can then be used in gluconeogenesis.