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Cell Physiology
Published in Wei-Shou Hu, Cell Culture Bioprocess Engineering, 2020
The lactate consumed by cells cannot be converted to glucose in most cultured cells. A number of reactions in glycolysis are irreversible. The conversion of pyruvate to glucose in the reverse direction of glycolysis, called gluconeogenesis, requires the expression of a few additional enzymes to counter these irreversible reactions. In mammals, gluconeogenesis primarily occurs in the liver. During the period that cells are consuming lactate, many intermediates derived from glycolysis are still needed for maintaining cellular functions. For example, dihydroxyacetone phosphate (DHAP) is needed for supplying glycerol 3-phosphate for lipid synthesis and NADPH, derived in the PPP, is needed for reductive biosynthesis and for maintaining the cell’s redox balance. Furthermore, glucose 6-phosphate is required to synthesize the glucosamine and galactose that are used in glycan synthesis for the production of recombinant proteins. The glycolysis pathway thus remains active during the lactate-consumption stage. The glucose consumption rate is small, but not zero (Panel 3.17).
Metabolic Engineering for the Production of a Variety of Biofuels and Biochemicals
Published in Kazuyuki Shimizu, Metabolic Regulation and Metabolic Engineering for Biofuel and Biochemical Production, 2017
Glycerol may be converted to dihydroxyacetone phosphate (DHAP) in the glycolysis by two routes, where one fermentative route converts glycerol to dihydroxyacetone (DHA) by glycerol dehydrogenase (GLDH) encoded by gldA and then DHA to DHAP by DHA kinase (DHAK) encoded by dhaKLM, while another respiratory route converts glycerol to glycerol 3-phosphate (GL3P) by glycerol kinase (GlpK) encoded by glpK, and then GL3P is converted to DHAP by aerobic GL3P dehydrogenase (GL3PDH) encoded by glpD (Durnin et al. 2009) (Fig. 5).
Utilization of glycerol and crude glycerol for polysaccharide production by an endophytic fungus Chaetomium globosum CGMCC 6882
Published in Preparative Biochemistry and Biotechnology, 2019
Zichao Wang, Tao Ning, Kun Gao, Xiaojia He, Huiru Zhang
As shown in Fig. 2C,D, the spore morphology of C. globosum CGMCC 6882 was found more favorable for polysaccharide production, this was similar to the general rules of microbial exo-polysaccharide synthesis, the exo-polysaccharide was synthesized during the stationary period for microorganism to protect it against environmental pressures.[16] The synthesis of biomass by C. globosum CGMCC 6882 from glycerol mainly through the pathways of glycerol phosphorylated to glycerol-3-phosphate by glycerol kinase, glycerol-3-phosphate oxidized to dihydroxyacetone phosphate by aerobic glycerol-3-phosphate dehydrogenase, dihydroxyacetone phosphate, and glyceraldehyde-3-phosphate aldolase to fructose-1,6-biphosphatase by fructose-1,6-biphosphatase aldolase, these pathways consumed a lot of energy,[17] meanwhile, the possible osmotic stress induced by glycerol made the mycelial cells more dispersed.[18] These might be the reason for long cell growth time, spore morphology, low cell dry weight, and high polysaccharide titer when C. globosum CGMCC 6882 used glycerol for polysaccharide production. When glucose was used as the sole carbon source, C. globosum CGMCC 6882 grew faster and easily formed large mycelia pellet and long hypha (Fig. 2A,B), thus leading to high cell dry weight and low polysaccharide titer. Interestingly, many researchers obtained similar results to this study, for instance, Lv et al.[19] and Chen et al.[20] found that the high production of Monascus pigments from Monascus species was associated with the formation of freely dispersed small mycelia pellets and short hyphae. Meanwhile, Driouch et al.[21] demonstrated that when titanate micro-particles were added into the growth medium, the pellet size of Aspergillus niger decreased from 1.7 to 0.3 mm, but the enzyme titer of glucoamylase produced by A. niger was 9.5-fold compared to the control group.
Mutagenesis of echinocandin B overproducing Aspergillus nidulans capable of using starch as main carbon source
Published in Preparative Biochemistry & Biotechnology, 2020
Zhong-Ce Hu, Wen-Jun Li, Shu-Ping Zou, Kun Niu, Yu-Guo Zheng
Generally, it is worth mentioning that microorganisms can utilize different carbon sources through different metabolism pathways. Carbon sources can often influence cell growth and metabolite production during fermentation processes. It was reported that mannitol and fructose were the traditional carbon sources for echinocandin B biosynthesis.[6] Obviously, starch is related to the metabolism of fructose and mannitol in A. nidulans, it transforms into fructose-6-phosphate under the function of glycogen phosphorylase, hexokinase and glucose-6-phosphate isomerase (Figure 2). And then fructose-6-phosphate can transform into fructose involved in the subsequent steps of glycolysis and enter mannitol cycle by mannitol-1-phosphate dehydrogenase (M1PDH) and mannitol-1-phosphatase (M1Pase).[31,32] Accordingly, starch, fructose and mannitol may have the similar metabolic processes, and can also provide enough energy for echinocandin B biosynthesis.[6] Altogether, these data provide indirect albeit support for carbon source replacement of fructose and mannitol by starch. Meanwhile, glycerol and peanut oil were also selected as carbon sources for echinocandin B fermentation. Glycerol as a kind of carbon source can be decomposed to glycerol-3-phosphate by glycerol kinase when strain is under starvation.[33] Then glycerol-3-phosphate transforms into 1, 3-diphosphoglycerate which leads to EMP pathway via dihydroxyacetone-phosphate. Using glycerol as carbon source was of benefit to mycelium growth at the beginning of fermentation. Furthermore, it was reported that glycerol might play a role in balancing the cellular osmoregulation and redox potential to regulate echinocandin B fermentation.[32,33] As we know, plant oil is also the common poor carbon source in antibiotic fermentation because it cannot be directly used by microorganisms.[3] Oil can be degraded to short-chain acyl-CoA, which can participate in biosynthesis of linoleic acid, the side chain of echinocandin B.