Keju Jing

Phototrophic cultivation of a thermo-tolerant Desmodesmus sp. for lutein production: Effects of nitrate concentration, light intensity and fed-batch operation

Four indigenous thermo-tolerant Desmodesmus sp. strains were examined for their ability to produce lutein. Among them, Desmodesmus sp. F51 was the best strain for this purpose. The medium composition, nitrate concentration and light intensity were manipulated to improve the phototrophic growth and lutein production of Desmodesmus sp. F51. It was found that a nitrogen-sufficient condition was required for lutein accumulation, while a high light intensity enhanced cell growth but caused a decrease in the lutein content. The best cell growth and lutein production occurred when the light intensity and initial nitrate concentration were 600 μmol/m(2)/s and 8.8 mM, respectively. The fed-batch cultivation strategy was shown to further improve lutein production. The highest lutein productivity (3.56±0.10 mg/L/d) and content (5.05±0.20 mg/g) were obtained when pulse-feeding of 2.2 mM nitrate was employed. This study demonstrated the potential of using Desmodesmus sp. F51 as a lutein producer in practical applications.

Fed-batch strategy for enhancing cell growth and C-phycocyanin production of Arthrospira (Spirulina) platensis under phototrophic cultivation

The C-phycocyanin generated in blue-green algae Arthrospira platensis is gaining commercial interest due to its nutrition and healthcare value. In this study, the light intensity and initial biomass concentration were manipulated to improve cell growth and C-phycocyanin production of A.platensis in batch cultivation. The results show that low light intensity and high initial biomass concentration led to increased C-phycocyanin accumulation. The best C-phycocyanin productivity occurred when light intensity and initial biomass concentration were 300μmol/m(2)/s and 0.24g/L, respectively. The fed-batch cultivation proved to be an effective strategy to further enhance C-phycocyanin production of A.platensis. The results indicate that C-phycocyanin accumulation not only requires nitrogen-sufficient condition, but also needs other nutrients. The highest C-phycocyanin content (16.1%), production (1034mg/L) and productivity (94.8mg/L/d) were obtained when using fed-batch strategy with 5mM medium feeding.

Direct proteomic mapping of Streptomyces roseosporus NRRL 11379 with precursor and insights into daptomycin biosynthesis

This first-attempt study provided liquid chromatography tandem mass (LC-MS/MS) proteomics approach to explore precursor effects on daptomycin synthesis from Streptomyces roseosporus NRRL 11379. Among all, 357 and 691 differential proteins from 601 proteins in precursor group (144 h+) and 935 proteins in non-precursor group (144 h-) were identified, respectively. Through the simulation of the 2D-protein mapping, most proteins were found in isoelectric points ranged of 4.5-10.0 as well as Mws ranged 10-100 kDa. As a result, LC-MS/MS analysis was consistence with the analytical results of two-dimensional electrophoresis (2DE) but provided much intact profiles of proteins by precursor effect on S. roseosporus. To have more insight exploration, differential proteins associated to Streptomyces spp. were defined into 14 groups of their functional classification. The major differential proteins were in transport/membrane functional group with an occupation of 12.4% for 144 h+ and 5.2% for 144 h-, respectively. LC-MS/MS results as a direct proteomic mapping approach reveal more daptomycin synthetic and regulation-related proteins from precursor group in terms of methyltransferase, ATP-binding cassette (ABC) transporters, resistance proteins and regulators.

Ammonium chloride: a novel effective and inexpensive salt solution for phycocyanin extraction from Arthrospira ( Spirulina ) platensis

Phycocyanin, a blue pigment, is a type of phycobiliproteins. Because of its various potential properties, phycocyanin is applied to various fields, such as nutraceutical, pharmaceutical, medicine, cosmetics, and biotechnological research. The cost and application of phycocyanin are highly dependent on its purity index. In this study, ammonium chloride is presented as a novel, effective, and inexpensive salt for phycocyanin extraction. Compared with sodium phosphate, which is commonly used during phycocyanin extraction process, ammonium chloride solution efficiently extracted phycocyanin with high purity from Arthrospira platensis FACHB-314. In addition, ammonium phosphate solution is also presented as an alternative precipitation agent in phycocyanin purification that may replace the widely used ammonium sulfate. Statistical analysis shows that there is no significant difference in phycocyanin concentration between crude extracts (overall mean of 0.208 and 0.215 for extraction using sodium phosphate and ammonium chloride, respectively). However, the difference in phycocyanin purity ratio (A620/A280) between these two extractions is significant (overall mean of 0.742 and 1.428 for extraction using sodium phosphate and ammonium chloride, respectively). With ammonium chloride, the purity indexes of phycocyanin are 1.5 and 2.81 after the optimum extraction step, and precipitation used as the primary purification step, respectively. The present study describes a novel purification method to achieve phycocyanin with analytical grade without multiple purification steps.

Use of biodiesel‐derived crude glycerol for vancomycin production by Amycolatopsis orientalis XMU‐VS01

Crude glycerol is a primary by‐product in the biodiesel industry. Microbial fermentation on crude glycerol for producing value‐added products provides opportunities to utilize a large quantity of this by‐product. This study investigates the potential of using the crude glycerol to produce vancomycin (glycopeptide antibiotics) through fermentation of Amycolatopsis orientalis XMU‐VS01. The results show that crude glycerol was the most effective carbon source for mycelium growth and vancomycin production, with 40–60 g/L glycerol concentration as optimal range. Among other culture medium components, potato protein (nitrogen source) and the phosphate concentration had significant effects (p<0.05) for vancomycin production. A Box‐Behnken design and response surface methodology were employed to formulate the optimal medium. Their optimal values were determined as 52.73 g/L of glycerol, 17.36 g/L of potato protein, and 0.1 g/L of dipotassium phosphate. A highest vancomycin yield of 7.61 g/L with biomass concentration of 15.8 g/L was obtained after 120 h flask fermentation. The yield of vancomycin was 3.5 times higher than with basic medium. The results suggest that biodiesel‐derived crude glycerol is a promising feedstock for production of vancomycin from A. orientalis culture.

Overproduction of L-tryptophan via simultaneous feed of glucose and anthranilic acid from recombinant Escherichia coli W3110: Kinetic modeling and process scale-up

L‐tryptophan is an essential amino acid widely used in food and pharmaceutical industries. However, its production via Escherichia coli fermentation suffers severely from both low glucose conversion efficiency and acetic acid inhibition, and to date effective process control methods have rarely been explored to facilitate its industrial scale production. To resolve these challenges, in the current research an engineered strain of E. coli was used to overproduce L‐tryptophan. To achieve this, a novel dynamic control strategy which incorporates an optimized anthranilic acid feeding into a dissolved oxygen‐stat (DO‐stat) glucose feeding framework was proposed for the first time. Three original contributions were observed. Firstly, compared to previous DO control methods, the current strategy was able to inhibit completely the production of acetic acid, and its glucose to L‐tryptophan yield reached 0.211 g/g, 62.3% higher than the previously reported. Secondly, a rigorous kinetic model was constructed to simulate the underlying biochemical process and identify the effect of anthranilic acid on both glucose conversion and L‐tryptophan synthesis. Finally, a thorough investigation was conducted to testify the capability of both the kinetic model and the novel control strategy for process scale‐up. It was found that the model possesses great predictive power, and the presented strategy achieved the highest glucose to L‐tryptophan yield (0.224 g/g) ever reported in large scale processes, which approaches the theoretical maximum yield of 0.227 g/g. This research, therefore, paves the way to significantly enhance the profitability of the investigated bioprocess.

Application of dodecahedron to describe the switching strategies of asynchronous simulated-moving-bed

Abstract Among various separation techniques, the simulated moving bed (SMB) process has received special attention, especially the asynchronous SMB that allocates the columns into four zones in a flexible way. With the relative switching times as variables in the Cartesian coordinates system, all applicable switching strategies in asynchronous SMB can be visualized in a dodecahedron with the initial configuration as the origin. Thus, any point in the dodecahedron represents a switching strategy, which could be easily obtained with initial configuration and coordinates. The dodecahedron includes 14 traditional SMB configurations, represented by the 14 vertexes of the dodecahedron. Based on the dodecahedron, the optimization of the asynchronous SMB was conducted through two case studies. Compared to traditional SMB, the feed flow rates were increased by 87% in the enantioseparation of 1,1′-bi-2-naphthol and 15% in the separation of glucose and fructose without the loss of product purities.

An efficient model construction strategy to simulate microalgal lutein photo-production dynamic process†

Lutein is a high‐value bioproduct synthesized by microalga Desmodesmus sp. It has great potential for the food, cosmetics, and pharmaceutical industries. However, in order to enhance its productivity and to fulfil its ever‐increasing global market demand, it is vital to construct accurate models capable of simulating the entire behavior of the complicated dynamics of the underlying biosystem. To this aim, in this study two highly robust artificial neural networks (ANNs) are designed for the first time. Contrary to conventional ANNs, these networks model the rate of change of the dynamic system, which makes them highly relevant in practice. Different strategies are incorporated into the current research to guarantee the accuracy of the constructed models, which include determining the optimal network structure through a hyper‐parameter selection framework, generating significant amounts of artificial data sets by embedding random noise of appropriate size, and rescaling model inputs through standardization. Based on experimental verification, the high accuracy and great predictive power of the current models for long‐term dynamic bioprocess simulation in both real‐time and offline frameworks are thoroughly demonstrated. This research, therefore, paves the way to significantly facilitate the future investigation of lutein bioproduction process control and optimization. In addition, the model construction strategy developed in this research has great potential to be directly applied to other bioprocesses. Biotechnol. Bioeng. 2017;114: 2518–2527.

Enhancement of cell growth and phycocyanin production in Arthrospira (Spirulina) platensis by metabolic stress and nitrate fed-batch

Arthrospira (Spirulina) platensis is known to have high-quality proteins content and phycocyanin as one of the major pigment constituents of the cells, and the most challenging problem associated with phycocyanin production in Arthrospira is to optimize its intracellular accumulation. The present study evaluated the metabolic stress conditions (by nutrient enrichment) of Arthrospira platensis FACHB-314 for boosting biomass growth and high content phycocyanin accumulation. Experimental results showed that 5 mM sodium glutamate and 7.5 mM succinic acid could enhance biomass yield as well as phycocyanin accumulation compared with that of the control groups. The present study demonstrates that the biomass growth and phycocyanin accumulation were significantly enhanced in fed-batch cultivation of Arthrospira platensis by applying the substrates as metabolic stress agents combined with nitrate feeding strategy. cobA/hemD, hemG and ho genes presented the over-expression level with adding sodium glutamate and succinic acid in cultures, respectively, compared to the control groups.

Solubility properties and diffusional extraction behavior of natamycin from streptomyces gilvosporeus biomass

Natamycin is a type of polyene macrolide antibiotic and has been produced in submerged microbial cultures of some natural Streptomyces strains. Natamycin extraction from cellular biomass is greatly affected by the molecular and solubilization characteristics of the extraction solvent, and this is a major reason for the routine attainment of low volumetric titers, resulting from sparing natamycin solubility. In this work, a series of experiments were conducted to investigate the solubility of natamycin in some selected organic solvents in order to assess the influence on natamycin extraction yield. Natamycin showed the highest solubility in 75% aqueous methanol under the conditions of pH 2, 30°C and 1 atm. Furthermore, the extraction of natamycin using 75% aqueous methanol was performed and the highest extraction yield of 45.7% was obtained under pH 2. A mathematical model derived from Ficks law of the biomolecular diffusion process was developed to fit the experimental kinetic data of natamycin extraction.