A modified metabolic model for mixed culture fermentation with energy conserving electron bifurcation reaction and metabolite transport energy

A modified metabolic model for mixed culture fermentation (MCF) is proposed with the consideration of an energy conserving electron bifurcation reaction and the transport energy of metabolites. The production of H₂ related to NADH/NAD⁺ and Fdred/Fdox is proposed to be divided in three processes in view of energy conserving electron bifurcation reaction. This assumption could fine‐tune the intracellular redox balance and regulate the distribution of metabolites. With respect to metabolite transport energy, the proton motive force is considered to be constant, while the transport rate coefficient is proposed to be proportional to the octanol–water partition coefficient. The modeling results for a glucose fermentation in a continuous stirred tank reactor show that the metabolite distribution is consistent with the literature: (1) acetate, butyrate, and ethanol are main products at acidic pH, while the production shifts to acetate and propionate at neutral and alkali pH; (2) the main products acetate, ethanol, and butyrate shift to ethanol at higher glucose concentration; (3) the changes for acetate and butyrate are following an increasing hydrogen partial pressure. The findings demonstrate that our modified model is more realistic than previous proposed model concepts. It also indicates that inclusion of an energy conserving electron bifurcation reaction and metabolite transport energy for MCF is sound in the viewpoint of biochemistry and physiology. Biotechnol. Bioeng. 2013; 110: 1884–1894. © 2013 Wiley Periodicals, Inc.     

酿酒酵母产苹果酸的还原TCA路径构建及发酵调控

苹果酸广泛应用于食品、化工行业。文中通过在酿酒酵母内敲除丙酮酸脱羧酶PDC1,并通过构建胞质内还原TCA的路径,即超表达丙酮酸羧化酶和苹果酸脱氢酶,成功地实现了苹果酸的生产。在野生型菌株中基本检测不到苹果酸的生成,而在工程菌株,苹果酸发酵浓度达到了45 mmol /L,同时副产物乙醇的产量也降低了18%。进一步通过发酵调控提高第二信使Ca2+的浓度使苹果酸的产量提高了7 %,在此基础上提高丙酮酸羧化酶的辅酶生物素浓度,使苹果酸的产量达到52.5 mmol /L,较原始菌株提高了16%。     

阿魏蘑液体发酵过程菌体形态变化对产漆酶的影响

本文旨在研究阿魏蘑菌体形态与漆酶产量之间的关系。结果显示,玻璃珠的添加可改变发酵过程中菌体形态,漆酶产量在球状菌体条件下高于丝状、絮状菌丝：直径分布在0.2~0.4 mm范围的菌球对漆酶的合成具有明显的促进作用;适合的葡萄糖、玉米粉和麸皮添加量,对直径在0.2~0.4 mm范围的菌球形成具有重要影响。此外,添加惰性载体同样可以控制菌球的直径分布,但对漆酶的合成无促进作用。     

Synthesis and Physiological Activity of Methyl 6′6′-Didemethyl Abscisate and New Chiral Analogs

Methyl 6′, 6′-didemethyl abscisate (5) was synthesized and assayed to elucidate the physiological activity of methyl substituents on the cyclohexene ring of abscisic acid (ABA). During this study two new chiral stereoisomeric analogs 6 and 7 were synthesized from l-and d-carvone. The rice seedling assay and germination assay of garden radish showed that 6′-methyl groups of ABA were not important in biological activity and that 5′-isopropenyl analogs 6 and 7 were inactive.     

Repeated Batch Production of Theanine by Coupled Fermentation with Energy Transfer Using Membrane-Enclosed γ-Glutamylmethylamide Synthetase and Dried Yeast Cells

γ-Glutamylmethylamide synthetase and dried baker’s yeast cells were enclosed together in a dialysis membrane tube to produce theanine repeatedly by coupled fermentation with energy transfer. The membrane-enclosed enzyme preparation (M-EEP) formed approximately 600 mM theanine from glutamic acid and ethylamine at a 100% conversion rate. M-EEP maintained its productivity of theanine during six consecutive reactions in a mixture containing NAD⁺.     

The Effect of Cocoa and Polydextrose on Bacterial Fermentation in Gastrointestinal Tract Simulations

Effects of cocoa mass and supplemented dietary fiber (polydextrose) on microbial fermentation were studied by combining digestion simulations of stomach and small intestine with multi-staged colon simulations. During the four phases of digestion, concentrations of available soluble proteins and reducing sugars reflected in vivo absorption of nutrients in small intestine. In colon simulation vessels, addition of polydextrose to digested cocoa mass significantly increased concentrations of total short-chain fatty acids and butyric acid, from 103 to 468 mM (P<0.01) and from 12 to 22 mM (P<0.01), respectively. Long-chain fatty acid concentrations (decreasing from 1,222 to 240 mM) were mainly affected by the presence of digested cocoa mass. Cocoa mass with or without polydextrose addition significantly decreased production of cadaverine (P<0.02) and branched-chain fatty acids compared to control during colon simulations. Results indicate beneficial effects on metabolism of colonic microbiota after digestion of cocoa mass, and even more so with polydextrose addition.     

Preparation of Optically Active Secondary Alcohols Related to Synthetic Pyrethroids by Microbial Asymmetric Hydrolysis of the Corresponding Acetates

Asymmetric hydrolysis of the acetates of racemic secondary alcohols related to synthetic pyrethroids by Bacillus subtilis var. niger (IFO 3108) yielded optically active acetates and alcohols of varying optical purities.     

4-Hydroxy-β-damascone and 4-Hydroxy-dihydro-β-damascone from Cigar Tobacco

The cDNA encoding a putative xylose reductase (xyrA) from Aspergillus oryzae was cloned and coexpressed in the yeast Saccharomyces cerevisiae with A. oryzae xylitol dehydrogenase cDNA (xdhA). XyrA exhibited NADPH-dependent xylose reductase activity. The S. cerevisiae strain, overexpressing the xyrA, xdhA, endogenous XKS1, and TAL1 genes, grew on xylose as sole carbon source, and produced ethanol.     

Complete Growth Inhibition of Bacillus subtilis by Nisin-Producing Lactococci in Fermented Soybeans

The growth inhibition by nisin-producing lactococci against Bacillus subtilis and its application to soybean miso fermentation were investigated. Lactococcus lactis subsp. lactis IFO12007 (nisin-producing, salt-intolerant) rapidly proliferated to more than 10⁹ cells/g in cooked soybeans without any excessive pH decrease. In spite of the mild decrease in pH, the growth of B. subtilis was completely inhibited; no living cells were detected in a soybean sample inoculated with 10⁶ cells/g and incubated for 24 to 72 h. This Lc. lactis was applied to soybean miso fermentation as a starter culture. It produced high nisin activity (1.28×10⁵ AU/g) in cooked soybean, resulting in the complete growth inhibition of B. subtilis, which had been inoculated at the beginning of the koji fermentation, throughout the process of miso production. Over-acidification, which is undesirable for miso quality, was successfully prevented simply by adding salt which killed the salt-intolerant Lc. lactis. Furthermore, the nisin activity in miso disappeared with aging.     

Production of 4-Keto-D-arabonate by Oxidative Fermentation with Newly Isolated Gluconacetobacter liquefaciens

Production of 4-keto-D-arabonate (4KAB) was confirmed in a culture medium of Gluconacetobacter liquefaciens strains, newly isolated from water kefir in Argentina. The strains rapidly oxidized D-glucose, D-gluconate (GA), and 2-keto-D-gluconate (2KGA), and accumulated 2,5-diketo-D-gluconate (25DKA) exclusively before reaching the stationary phase. 25DKA was in turn converted to 4KAB, and 4KAB remained stable in the culture medium. The occurrence of 4KAB was assumed by Ameyama and Kondo about 50 years ago in their study on the carbohydrate metabolism of acetic acid bacteria (Bull. Agr. Chem. Soc. Jpn., 22, 271–272, 380–386 (1958)). This is the first report confirming microbial production of 4KAB.