Reconstruction of the Diaminopimelic Acid Pathway to Promote L-lysine Production in Corynebacterium glutamicum

The dehydrogenase pathway and the succinylase pathway are involved in the synthesis of L-lysine in Corynebacterium glutamicum. Despite the low contribution rate to L-lysine production, the dehydrogenase pathway is favorable for its simple steps and potential to increase the production of L-lysine. The effect of ammonium (NH4+) concentration on L-lysine biosynthesis was investigated, and the results indicated that the biosynthesis of L-lysine can be promoted in a high NH4+ environment. In order to reduce the requirement of NH4+, the nitrogen source regulatory protein AmtR was knocked out, resulting in an 8.5% increase in L-lysine production (i.e., 52.3 ± 4.31 g/L). Subsequently, the dehydrogenase pathway was upregulated by blocking or weakening the tetrahydrodipicolinate succinylase (DapD)-coding gene dapD and overexpressing the ddh gene to further enhance L-lysine biosynthesis. The final strain XQ-5-W4 could produce 189 ± 8.7 g/L L-lysine with the maximum specific rate (qLys,max.) of 0.35 ± 0.05 g/(g·h) in a 5-L jar fermenter. The L-lysine titer and qLys,max achieved in this study is about 25.2% and 59.1% higher than that of the original strain without enhancement of dehydrogenase pathway, respectively. The results indicated that the dehydrogenase pathway could serve as a breakthrough point to reconstruct the diaminopimelic acid (DAP) pathway and promote L-lysine production.

Reconstruction of the Diaminopimelic Acid Pathway to Promote L-lysine Production in Corynebacterium Glutamicum

Background: The dehydrogenase pathway and the succinylase pathway are involved in the synthesis of L-lysine in Corynebacterium glutamicum. Despite the low contribution rate to L-lysine production, the dehydrogenase pathway is favorable for its simple steps and great potentials to increase the production of L-lysine. Results: The aim of this work is to enhance the carbon flux in dehydrogenase pathway to promote L-lysine production. Firstly, the effect of ammonium (NH4+) concentration on L-lysine biosynthesis was investigated, and the results indicated that the biosynthesis of L-lysine can be promoted in high NH4+ environment. In order to reduce the requirement of NH4+, the nitrogen source regulatory protein AmtR was knocked out, resulting in an 8.5% increase in L-lysine production (i.e., 52.3±4.31 g/L). Subsequently, the dehydrogenase pathway was upregulated by blocking or weakening tetrahydrodipicolinate succinylase (DapD)-coding gene dapD and overexpressing the ddh gene to further enhance L-lysine biosynthesis. The final strain XQ-5-W4 could produce 189±8.7 g/L L-lysine with the maximum specific rate (qLys,max.) of 0.35±0.05 g/(g·h) in a 5-L jar fermenter. Conclusions: The L-lysine titer and qLys,max achieved in this study is about 25.2% and 59.1% higher than that of the original strain without enhancement of dehydrogenase pathway, respectively. The results indicated that the dehydrogenase pathway could serve as a breakthrough point to reconstruct the diaminopimelic acid (DAP) pathway and promote L-lysine production.

Preparation procedure to obtain iron nanopowder under non-isothermal conditions

The kinetics for the procedure of preparing iron nanopowder from α-FeOOH by hydrogen reduction under non-isothermal conditions were studied. The reduction of α-FeOOH nanopowder was shown to occur within the temperature range from 180 to 550 °С, with a maximum specific rate value attained at 500 °С. The activation energy for the reduction process α-FeOOH nanopowder was measured to be ~43 kJ/mol, evidencing a mixed reaction mode. Performing the reduction of α-FeOOH at 500 °С accelerated the process while ensuring the required properties of the product obtained. The Fe nanoparticles thus prepared were of rounded shape, the size ranging from 70 to 100 nm.

Dynamics Modeling of Nitrogen Compounds in Microalgae Cells. 2. Chemostat

The work focuses on dynamics modeling of nitrogen compounds in microalgae cells under chemostat conditions. The analysis of classical models (Michaelis-Menten, Monod, Droop), which describe the kinetics of substrate-dependent growth of microalgae, was carried out. Classical models are shown to be applicable provided that the physicochemical parameters of the medium such as temperature, cell irradiation, etc are constant. As an alternative approach, the possibility of using linear splines in kinetics modeling of nitrate absorption by microalgae is shown. For the conditions of the chemostat, particular solutions for the generalized model of the dynamics of nitrogen compounds in the cells of microalgae considered in the first part of the work were obtained, and boundary conditions for the culture growth at unlimited nitrogen were determined. For limited growth, the equation for both the dependence of the specific growth rate on the intracellular nitrogen content, which coincides in form with the Droop model and the dependence of the specific growth rate on the extracellular concentration of nitrogen, which coincides in form with the Monod model were obtained. The species-specific coefficients of the equations such as the maximum specific rate of nitrogen absorption, the maximum specific rate of synthesis of structural components, the maximum content of reserve forms of nitrogen, the minimum share of structural forms of nitrogen in the total cell content were determined.

Degradation biokinetics of used and fresh lube oils in contaminated soil environment

In order to solve the problems of the soil environment caused by the discharge of petroleum products especially oils used for lubrication, investigations were carried out to assess the degradation of fresh and used lube oil in soil environment using bacteria degraders present in the soil. This was done by introducing some quantities of the pollutant (fresh and used lubricating oils) into some soil samples obtained from the environment. The degradation pattern was studied by estimating the level of the microbial growth using culture method and the phenol content. This was done before the introduction of the pollutant and at two weekly intervals for 42days. Results show that the phenol content, microbial and micro species present in the soil rapidly increased to maximum and then declined. The specific rate, maximum specific rate and equilibrium constants were determined using Line-Weaver Burk Plots. Results obtained show that the bacteria which degraded the fresh and used lube oil were inhibited by the presence of phenol which was informed during the biodegradation reaction. Empirical equation for microbial growth rate using the data from the experiment was obtained. The degradation of the fresh lube oil occurred faster than the used lube oil. The equation is useful in monitoring and predicting the performance of microorganisms in bioreactor and predicting the performance of microorganisms in bioreactor containing used or fresh lube oil.

Development of model for bioremediation of crude oil using moringa extract

Crude oil spillage on land is a major undeniable challenge we face in the Niger Delta, this is as a result of the oil exploration and exploitation activity done by the big oil multinationals and also those done by indigenous private firms, the petroleum could find its way to the soil via occurrences including pipeline leakages and explosions, corrosion of underground pipes transporting crude oil and petroleum product and also it could come purely in form of untreated industrial waste. As a result of the foregoing research work was conducted using Moringa leave extract, and the component of interest included phosphates, potassium and nitrogen which are the major stimulators of bioremediation, were found to be abundant in the Moringa Oleifera leave extract. The application of Moringa leave extract was found to be useful in the enhancing of crude oil polluted lands, and by so doing it facilitates the rehabilitation of the contaminated soil as well as reinstating the soil constituents for agricultural purposes. This is a new research investigation which show high efficiency in bioremediation program the maximum specific rate and the rate constants as well as they overall order of the bioremediation reaction were determined, using the principle of the rate laws as well as they Monod’s equation from which the line waver burke plot was obtained. Therefore the experiment as well as the theoretical model developed can be used to monitor, predict and simulate the rate of degradation of hydrocarbons present in a polluted soil undergoing bioremediation under the influence of Moringa Oleifera leave extract.

Spent sulphite liquor utilization by xylose-assimilating yeast pachysolen tannophilus, capable of bioethanol producing

The xylose-assimilating capacity of yeast Pachysolen tannophilus to utilize sugars in spent sulphite liquor samples (pulp mill waste) with a different concentration of hexoses and pentoses was studied. The consumption of hexoses (D-glucose, D-mannose, D-galactose) and pentose (D-xylose) in such substrates reached 90.0-97.5% and 49.12-67.45%, respectively. The ethanol production from sugars in spent sulphite liquor by different strains of the yeast P. tannophilus was demonstrated. The maximum specific rate and ethanol yield reached 9.32-11.45 g l-1 and 0.28-0.37 g g sugars-1, respectively. Thus, the principle possibility of using xylose-assimilating P. tannophilus yeast to obtain bioethanol from sulfite liquor with a different ratio of hexoses and pentoses was proved. According to theoretical calculations, this method will provide up to 42.6 liters of ethanol from 100 kg of sulfite liquor containing 55.6% D-xylose, 24.7% D-glucose, 8.7% D-mannose, 7.6% D-galactose, 3.7% L-arabinose. A future-oriented perspective on bioethanol production from pulp and paper industry wastes by the yeast P. tannophilus is considered.

Modeling of Dynamics of Nitrogenous Compounds in Microalgae Cells. 1. Batch Culture

The work is focused on modeling of dynamics of nitrogenous compounds in microalgae cells. The model is based on the idea that all intracellular nitrogen can be considered as the sum of structural and reserve forms. The rate of nitrogen supply into the cell and the rate of its consumption for the synthesis of structural components are described in the form of linear splines and expressed through the ratio of reserve and structural forms. It is shown that species-specific parameters of the model are light-dependent values. Particular integrated solutions have been found for specific cases of nitrogen supply. The dynamics of all forms of intracellular nitrogen and nitrogen concentration in the medium follow the exponential law. The mathematical model for quantitative description of microalgae culture growth in the absence of nitrogen in the environment is proposed. The equations obtained using experimental data on the culture growth and nitrogen assimilation by cells of green microalgae Dunaliella salina and Scenedesmus obliquus have been verified. The proposed model allows to describe the dynamics of the concentration changes of structural, reserve and extracellular nitrogen in the cultivation of these species. For the exponential growth phase, the species-specific coefficients of the maximum specific rate of nitrogen supply into the cell and the maximum specific rate of the synthesis of structural components, which for D. salina amounted to: 0.42 day-1 and 0.55 day-1; for S. obliquus – 1.37 day-1 and 1.25 day-1 respectively have been determined. Differences of these parameters for two types of microalgae are due to different light conditions of their cultivation.

Lipid peroxide formation in microsomes. General considerations

1. Liver microsomes form lipid peroxide when incubated with ascorbate or NADPH, but not with NADH. Increasing the concentration of ascorbate beyond the optimum (0·5mm) decreases the rate of lipid peroxide formation, but this effect does not occur with NADPH. Other reducing agents such as p-phenylenediamine or ferricyanide were not able to replace ascorbate and induce lipid peroxide formation. 2. The rate of ascorbate-induced peroxidation is optimum at pH6·0 whereas the rate of the NADPH system is optimum at pH7·0. Both systems require phosphate for maximum activity. 3. Lipid peroxide formation occurs at the maximum specific rate in very dilute microsome suspensions (0·15mg. of protein/ml.). 4. Treatment of microsomes with deoxycholate and other detergents causes membrane disintegration and inhibits lipid peroxide formation. 5. Lipid peroxide formation is accompanied by a rapid uptake of oxygen and there is a large excess of oxygen utilized for each molecule of malonaldehyde measured in the peroxide method. 6. Boiled microsomes form lipid peroxide in the presence of ascorbate, but not if NADPH is added. 7. Lipid peroxide formation induced by NADPH is strongly inhibited by p-chloromercuribenzoate, weakly inhibited by N-ethylmaleimide and unaffected by iodoacetamide. Ascorbate-induced peroxidation in untreated microsomes is unaffected by p-chloromercuribenzoate, but inhibited if boiled microsomes are used. These experiments may be interpreted on the basis that a ferredoxin-type protein forms part of the system in which NADPH induces lipid peroxide formation. 8. Most heavy-metal ions, with the exception of inorganic iron (Fe2+ or Fe3+), which activates, inhibit both ascorbate-induced and NADPH-induced peroxidation. Mg2+ increases the rate of peroxidation whereas Ca2+ inhibits it. 9. Lipid peroxide formation is inhibited strongly by GSH and weakly by cysteine. Ascorbate-induced peroxidation is much more sensitive than NADPH-induced peroxidation. 10. Peroxidation is strongly inhibited by addition of low concentrations (0·01–0·1mm) of cytochrome c or of haemoglobin. 11. It is considered that lipid peroxide formation occurs as a result of the operation of the microsomal electron-transport chain switching from hydroxylation to oxidize unsaturated lipids of the endoplasmic reticulum.