初始底物浓度对序批式培养光合细菌产氢动力学影响

实验研究了初始底物浓度对序批式培养光合细菌生长、降解及产氢过程的影响,根据最大比生长速率实验数据拟合得到其关于初始底物浓度影响的关联式,并在建立的修正Monod模型基础上建立了光合细菌比生长速率、基质比消耗速率和比产氢速率关于底物初始浓度影响的数学模型,模型预测值与实验结果在光合细菌生长期和稳定期内得到较好吻合,反映了光合细菌生长、降解和产氢过程中受底物初始浓度限制性和抑制性影响的基本规律。分析发现光合细菌生长、降解基质和产氢过程中最适底物浓度为50 mmol/L,初始底物浓度低于或高于该浓度时,光合细菌生长、降解及产氢过程都受到限制性或抑制性影响,且抑制性影响较限制性影响效果更明显;底物比消耗速率受初始底物浓度影响较小。     

Optimization of sorbose production from sorbitol by Gluconobacter oxydans

The basic parameters were studied influencing the conversion of orbitol to sorbose by Gluconobacter oxydans(industrial strain from FARMAKON Co., Czechoslovakia). The most effective conversion in the stationary phase was reached at pH 5.0, no inhibitory effect of sorbitol in a concentration ranging from 20 to 200 g/l and a minimum inhibitory effect of the sorbose concentration up to 200 g/l were observed. According to the optimum conditions mentioned above the optimized course of the fed-batch cultivation was proposed. The final concentration of sorbose of 410 g/l was reached after 36 hours.     

新组合菌系SCB329-SCB933利用L-山梨糖发酵产生维生素C前体2-酮基-L-古龙酸的研究Ⅲ.发酵过程的特征和条件控制

在分析了新组合菌系ＳＣＢ３２９－ＳＣＢ９３３发酵过程特征的基础上,对流加发酵工艺中的种子培养、ｐＨ、溶氧的控制,以及发酵液初始培养基中的Ｌ－山梨糖浓度和流加起始点进行了优化,获得了比分批发酵更为满意的结果：发酵最终总糖达１３％（ｗ／ｖ）左右,发酵周期４０～５０ｈ,产２－酮基－Ｌ－古龙酸达１１５－１３０ｍｇ／ｍｌ,克分子转化率达８８ｍｏｌ％左右。     

Regulation of sugar transport systems of Kluyveromyces marxianus: the role of carbohydrates and their catabolism

In Kluyveromyces marxianus grown on a glucose-containing synthetic medium four different sugar transporters have been identified. In cells, harvested during the exponential phase, only the constitutive glucose/fructose carrier, probed with 6-deoxy-D-glucose or sorbose, appeared to be active. In cells from the stationary phase three proton symporters can be active, recognizing 6-deoxyglucose (a glucose/galactose carrier), sorbose (a fructose carrier) and galactosides (lactose carrier), respectively. These symporters appeared to be sensitive to catabolite inactivation. This process is induced by incubating cells in the presence of glucose, fructose or mannose. Catabolite inactivation was not influenced by the inhibitor of protein synthesis, anisomycin. Derepression of the proton/sorbose and the proton/galactoside symporters proceeded readily when cells were incubated in a medium without glucose. Activation of the proton/galactose symporter needed, in addition, the presence of specific molecules (inducers) in the medium. The activation of each of these active transport systems was inhibited by anisomycin, showing the involvement of protein synthesis.     

Fed-batch sorbitol to sorbose fermentation by A. suboxydans

Batch kinetics for sorbitol to sorbose bioconversion was studied at 20% sorbitol concentration. The culture featured 90% conversion of sorbitol to sorbose in 20 hours. Increasing the initial substrate concentration in the bioreactor decreased the culture specific growth rate. At 40% initial sorbitol concentration no culture growth was observed. The batch kinetics and substrate inhibition studies were used to develop the Mathematical Model of the system. The model parameters were identified using the original batch kinetic data (S _o =20%). The developed mathematical model was adopted to fed-batch cultivation with the exponential nutrient feeding. The fed-batch model was simulated and implemented experimentally. No substrate inhibition was observed in the fed-batch mode and it provided an overall productivity of 12.6?g/l-h. The fed-batch model suitably described the experimentally observed results. The model is ready for further optimization studies.     

Fed-batch sorbose fermentation using pulse and multiple feeding strategies for productivity improvement

Microbial oxidation of D-sorbitol tol-sorbose byAcetobacter suboxydans is of commercial importance since it is the only biochemical process in vitamin C synthesis. The main bottleneck in the batch oxidation of sorbitol to sorbose is that the process is severely inhibited by sorbitol. Suitable fed-batch fermentation designs can eliminate the inherent substrate inhibition and improve sorbose productivity. Fed-batch sorbose fermentations were conducted by using two nutrient feeding strategies. For fed-batch fermentation with pulse feeding highly concentrated sorbitol (600 g/L) along with other nutrients were fed intermittently in four pulses of 0.5 liter in response to the increased DO signal. The fed-batch fermentation was over in 24 h with a sorbose productivity of 13.40 g/L/h and a final sorbose concentration of 320.48 g/L. On the other hand, in fed-batch fermentation with multiple feeds, two pulse feeds of 0.5 liter nutrient medium containing 600 g/L sorbitol was followed by the addition of 1.5 liter nutrient medium containing 600 g/L sorbitol at a constant feed rate of 0.36 L/h till the full working capacity of the reactor. The fermentation was completed in 24 h with an enhanced sorbose productivity of 15.09 g/L/h and a sorbose concentration of 332.60 g/L. The sorbose concentration and productivity obtained by multiple feeding of nutrients was found to be higher than that obtained by pulse feeding and was therefore a better strategy for fed-batch sorbose fermentation.     

A density functional theory study of the decomposition mechanism of nitroglycerin

The detailed decomposition mechanism of nitroglycerin (NG) in the gas phase was studied by examining reaction pathways using density functional theory (DFT) and canonical variational transition state theory combined with a small-curvature tunneling correction (CVT/SCT). The mechanism of NG autocatalytic decomposition was investigated at the B3LYP/6-31G(d,p) level of theory. Five possible decomposition pathways involving NG were identified and the rate constants for the pathways at temperatures ranging from 200 to 1000 K were calculated using CVT/SCT. There was found to be a lower energy barrier to the β-H abstraction reaction than to the α-H abstraction reaction during the initial step in the autocatalytic decomposition of NG. The decomposition pathways for CHOCOCHONO₂ (a product obtained following the abstraction of three H atoms from NG by NO₂) include O–NO₂ cleavage or isomer production, meaning that the autocatalytic decomposition of NG has two reaction pathways, both of which are exothermic. The rate constants for these two reaction pathways are greater than the rate constants for the three pathways corresponding to unimolecular NG decomposition. The overall process of NG decomposition can be divided into two stages based on the NO₂ concentration, which affects the decomposition products and reactions. In the first stage, the reaction pathway corresponding to O–NO₂ cleavage is the main pathway, but the rates of the two autocatalytic decomposition pathways increase with increasing NO₂ concentration. However, when a threshold NO₂ concentration is reached, the NG decomposition process enters its second stage, with the two pathways for NG autocatalytic decomposition becoming the main and secondary reaction pathways.     

微生物生活周期中的一个新的时期——长期稳定期

传统的对微生物生长时期的认识一般分为4个时期:迟缓期、对数期、稳定期、死亡期。实际上,这种划分不足以使我们认识到微生物生长过程的全貌。近年来许多研究表明,在死亡期之后存在一个完全不同意义的时期——长期稳定期。这个时期可能与微生物在环境中的生存状态更加相似。微生物细胞通过突变得以生存,并在选择中形成稳定期生长优势表型,深入研究微生物长期稳定期具有极其重要的意义。     

The disruption of Alcaligenes eutrophus by high pressure homogenisation: key factors involved in the process.

The disruption of the Gram-negative bacterium Alcaligenes eutrophus by high pressure homogenisation, using the APV Gaulin 15M 8BA and 30CD homogenisers is reported. The operating parameters such as operating pressure, number of passes, temperature and biomass concentration, mimicked trends previously reported for yeasts. Extension of the study to consider the effect of cell characteristics, including the growth rate, size and shape, illustrated the dominant effect of the growth phase. The improved disruption of bacterial cultures in the logarithmic phase with respect to stationary phase cultures was confirmed by an increased dependence of actively growing cultures on the operating pressure. An increase in size in excess of 30% on the accumulation of the storage product, PHB in the stationary phase caused little change in the ease of disruption. The use of transmission electron microscopy to directly monitor the disruption on multiple passes shed light on the two-stage nature of this disruption process.     

Continued growth of Escherichia coli after stopping medium addition to a K+-limited chemostat culture

The steady-state bacterial dry wt of Escherichia coli, growing under K+-limited conditions in the chemostat, was inversely dependent on the growth rate. This phenomenon was more carefully investigated in medium-flow stop experiments. Growth did not stop immediately but continued for a time, initially at the same rate as before. The dry wt increased to a value corresponding to a steady-state growth rate near zero, independent of the initial specific growth rate. This was observed in both the wild-type strain and a mutant that lacked the high-affinity K+ uptake system. The wild-type strain maintained a low extracellular K+ concentration both in the chemostat under steady-state conditions and after stopping the medium flow. The mutant, on the other hand, maintained a much higher extracellular K+ concentration in the steady state, which decreased to much lower values after stopping the medium flow. From the increase in bacterial dry wt and the low external K+ concentration after stopping the medium flow it is concluded that the intracellular K+ is redistributed among the cells, including new cells. The growth yield on K+ was highest in the stationary growth phase of a batch culture and all steady-state cultures converged ultimately to this yield value after the medium flow had been stopped. It is proposed that the growth rate of E. coli under K+-limited conditions is determined by the intracellular K+ concentration.     

Kinetics of the AHL regulatory system in a model biofilm system: how many bacteria constitute a "quorum"?

Acylated homoserine lactones (AHLs) regulate a wide variety of phenotypes in Gram-negative bacteria. Most research suggests that AHL-mediated phenotypes are not expressed in populations until late logarithmic phase or stationary phase. Here, we model how the concentration of AHLs inside bacterial cells and in a biofilm changes over time as a function of population growth rate, diffusion of AHLs and the rate of autoinduction. Our theoretical results show that the concentration of AHLs inside a single bacterium (and by implication induction of a phenotype) has a non-trivial behaviour over time, and often exhibits a rapid increase early in population growth. This rapid increase is followed by a plateau, followed by another rise in the concentration of AHLs, to a second plateau. High concentrations of AHLs inside the bacterial cell early in population growth are positively affected by slow diffusion rates out of the cell and the biofilm, slow bacterial growth rates and fast autoinduction. In contrast, fast growth rates, slow autoinduction rates and high diffusion rates result in a high concentration plateau in stationary phase. More generally, the density-dependent nature of AHL regulation can be viewed as a trade-off between factors that dilute intracellular concentrations of AHLs (diffusion out of the cell, cell division), and those that increase concentrations (a slowing or restriction of diffusion or growth, or autoinduction). These results suggest that expression of AHL-mediated phenotypes can occur at relatively low cell densities and low external/environmental AHL concentrations.     

Combined effect of gamma-irradiation and sodium nitrite on the oxidative sensitivity of rat hemoglobin

gamma-Irradiation has been defined to increase in the rats blood the methemoglobin level providing for shortening the initiation phase and accelerates the autocatalytic phase initiation, reduces the period of half transforming hemoglobin into methemoglobin and increases the velocity of its oxidation. Alongside with the latter there is observed a violation of methemoglobin concentration growth dependence on the animals irradiation dose (in the range of 0.16-0.50 Gr). The hemoglobin oxygenation reaction kinetics with the initial level of hemoglobin unexceeding 3% has been determined as having a biexponential character. The reaction kinetics parameters don't depend on ionizing radiation and number of sodium nitrite oxidized subunits formed in the process of reaction in the case if their composition unexceeds 50% of the total level.     

Fed-batch cultivation of Acetobacter suboxydans for the microbial oxidation of D-sorbitol to L-sorbose

Microbial oxidation of D-sorbitol to L-sorbose is commercially important since it is the only biochemical process in Vitamin-C manufacture. The main bottleneck in the batch oxidation of D-sorbitol is that the process is severely inhibited by sorbitol. By conducting fed-batch fermentation, the inherent substrate inhibition present in batch fermentation can be eliminated. Batch fermentation with an initial sorbitol concentration of 200 g l^у featured a productivity of 14.2 g l^у h^у and a final sorbose concentration of 200 g l^у. Fed-batch fermentation conducted by feeding nutrients containing 600 g l^у of sorbitol at a constant feed rate of 0.36 l h^у yielded a productivity of 17.7 g l^у h^у and a final sorbose concentration of 320 g l^у.     

An autocatalytic model for bacterial spore germination.

The sigmoidal response observed in kinetic studies of germinating bacterial spores, using nephelometric techniques and phase contrast microscope photometry, is analysed by postulating an autocatalytic process. A scheme A to B to C, where B catalyses the degradation of A, is applied to describe the response accurately by three rate constants. The autocatalytic model is compared with previous proposals for quantifying germination studies and for interpreting the effect of different experimental conditions on initiation of germination. Its effectiveness is demonstrated by quantifying published results for a germinating single spore determined by phase contrast microscopy, and nephelometric results for spore suspensions, including the effect of temperature on the rate of initiation of germination. Although developed for quantitative analysis of spore germination, the model is applicable to other autocatalytic phenomena. To assist the experimentalist, a simple accurate method for deriving the three constants specifying the sigmoidal characteristic is described.     

Effect of Growth Conditions on Yield and Heme Content of Vitreoscilla

Vitreoscilla, a gliding bacterium in the Beggiatoaceae, is an obligate aerobe in which cytochrome o functions as the terminal oxidase. Protoheme IX is the only heme type present in this organism. The yield and heme content of Vitreoscilla cells grown in yeast extract, peptone, and acetate were dependent on growth conditions. Cells harvested in early stationary phase contained roughly three times as much heme as cells in early log phase. There was an optimal shaking rate for maximum heme content of cells harvested in stationary phase at fixed initial nutrient concentration. The heme content of cells grown at a fixed shaking rate increased from 5 nmol/g (wet weight) in media which had low nutrient concentration to a maximum of 45 nmol/g (wet weight) in media which had high nutrient concentration, and there was a corresponding sixfold increase in cytochrome o content and an eightfold increase in respiratory rate, evidence that some of the additional heme was incorporated into respiratory pigments. Heme content may be controlled jointly by competition for oxygen and availability of nutrients. Temperature and initial pH affected the growth rate but not the final yield or heme content. Growth rate was optimal at pH 8.0 to 8.5. A defined medium for Vitreoscilla, which is based on glutamate as the carbon source, is described; the other organic components of this medium are acetate, tryptophan, thiamine, biotin, and riboflavin.     

Control of Escherichia coli growth rate through cell density

The transition from the exponential to the stationary phase of Escherichia coli cultures has been investigated regarding nutrient availability. This analysis strongly suggests that the declining of the cell division rate is not caused by mere nutrient limitation but also by an immediate sensing of cell concentration. In addition, both the growth rate and the final biomass achieved by a batch culture can be manipulated by altering its density during the early exponential phase. This result, which has been confirmed by using different experimental approaches, supports the hypothesis that the E. coli quorum sensing is not only determined by the release of soluble cell-to-cell communicators. Cell-associated sensing elements might also be involved in modulating the bacterial growth even in the presence of non-limiting (although declining) nutrient concentrations, thus promoting their economical utilisation in dense populations.     

Degradation of uric acid during autocatalytic oxidation of oxyhemoglobin induced by sodium nitrite.

The oxidation of oxyhemoglobin produced by sodium nitrite occurs in two stages: 1) an initial slow phase followed by 2) a rapid autocatalytic phase that carries the reaction to completion. The length of the slow phase is extended when uric acid is added to the reaction mixture. As the concentration of uric acid increases, the length of the slow phase increases until a concentration is reached at which the rate of methemoglobin formation is nearly linear until the reaction is complete. Further increases in the concentration of uric acid do not affect the rate of the reaction in the slow phase. At low concentrations of uric acid, where an autocatalytic phase is reached, uric acid is degraded during the reaction. At concentrations of uric acid that keep the reaction in the linear phase, the uric acid is not degraded. It is concluded that uric acid may protect oxyhemoglobin by reacting with HbO2H to yield [HbOH]+ and the urate radical. The urate radical may react with a second molecule of HbO2H and become oxidized. At higher concentrations, the radical may undergo electron transfer with oxyhemoglobin to regenerate the uric acid and form methemoglobin.     

Ion metabolism in a Halobacterium. I. Influence of age of culture on intracellular concentrations

Work is described on the changes in cell ions during growth of cultures of a species of Halobacterium isolated from the Dead Sea. Cell K concentration fell from 5.5 to 3.8 moles per kg cell water during the logarithmic phase of growth and maintained the latter value during the stationary phase (initial medium concentration, 7 mM). Cell Na and Cl followed a complex series of roughly parallel changes. The logarithmic phase ion concentrations were: Na, 1.0–2.3 moles/kg cell water; Cl, 2.3–3.7 moles/kg cell water. The final stationary phase values were: Na, 0.5 moles/kg cell water; Cl, 2.3–2.9 moles/kg cell water (medium NaCl concentration, 3.9 Molal). It is suggested that most of the K⁺ is bound within the cytoplasm.