Automated fed-batch culture of recombinant Saccharomyces cerevisiae based on on-line monitored maximum substrate uptake rate

Production of polyunsaturated fatty acids by Schizochytrium (Aurantiochytrium) spp

Diverse health benefits are associated with dietary consumption of omega-3 long-chain polyunsaturated fatty acids (ω-3 LC-PUFA), particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Traditionally, these fatty acids have been obtained from fish oil, but limited supply, variably quality, and an inability to sustainably increase production for a rapidly growing market, are driving the quest for alternative sources. DHA derived from certain marine protists (heterotrophic thraustochytrids) already has an established history of commercial production for high-value dietary use, but is too expensive for use in aquaculture feeds, a much larger potential market for ω-3 LC-PUFA. Sustainable expansion of aquaculture is prevented by its current dependence on wild-caught fish oil as the source of ω-3 LC-PUFA nutrients required in the diet of aquacultured animals. Although several thraustochytrids have been shown to produce DHA and EPA, there is a particular interest in Schizochytrium spp. (now Aurantiochytrium spp.), as some of the better producers. The need for larger scale production has resulted in development of many strategies for improving productivity and production economics of ω-3 PUFA in Schizochytrium spp. Developments in fermentation technology and metabolic engineering for enhancing LC-PUFA production in Schizochytrium spp. are reviewed.

Quantification of the oxygen uptake rate in a dissolved oxygen controlled oscillating jet-driven microbioreactor

BACKGROUND

Microbioreactors have emerged as a new tool for early bioprocess development. The technology has advanced rapidly in the last decade and obtaining real-time quantitative data of process variables is nowadays state of the art. In addition, control over process variables has also been achieved. The aim of this study was to build a microbioreactor capable of controlling dissolved oxygen (DO) concentrations and to determine oxygen uptake rate in real time.

RESULTS

An oscillating jet driven, membrane-aerated microbioreactor was developed without comprising any moving parts. Mixing times of ∼7 s, and k_La values of ∼170 h^-1 were achieved. DO control was achieved by varying the duty cycle of a solenoid microvalve, which changed the gas mixture in the reactor incubator chamber. The microbioreactor supported Saccharomyces cerevisiae growth over 30 h and cell densities of 6.7 g_dcw L^-1. Oxygen uptake rates of ∼34 mmol L^-1 h^-1 were achieved.

CONCLUSION

The results highlight the potential of DO-controlled microbioreactors to obtain real-time information on oxygen uptake rate, and by extension on cellular metabolism for a variety of cell types over a broad range of processing conditions. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Enhanced rhamnolipid production by Pseudomonas aeruginosa USM-AR2 via fed-batch cultivation based on maximum substrate uptake rate

A fed-batch strategy was established based on the maximum substrate uptake rate (MSUR) of Pseudomonas aeruginosa USM-AR2 grown in diesel to produce rhamnolipid. This strategy matches the substrate feed rates with the substrate demand based on the real-time measurements of dissolved oxygen (DO). The MSUR was estimated by determining the time required for consumption of a known amount of diesel. The MSUR trend paralleled the biomass profile of Ps. aeruginosa USM-AR2, where the MSUR increased throughout the exponential phase indicating active substrate utilization and then decreased when cells entered stationary phase. Rhamnolipid yield on diesel was enhanced from 0·047 (g/g) in batch to 0·110 (g/g) in pulse-pause fed-batch and 0·123 (g/g) in MSUR fed-batch. Rhamnolipid yield on biomass was also improved from 0·421 (g/g) in batch, 3·098 (g/g) in pulse-pause fed-batch to 3·471 (g/g) using MSUR-based strategy. Volumetric productivity increased from 0·029 g l(-1) h(-1) in batch, 0·054 g l(-1) h(-1) in pulse-pause fed-batch to 0·076 g l(-1) h(-1) in MSUR fed-batch.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study highlights the significance of an effective fed-batch strategy for rhamnolipid production in a submerged fermentation using a water-immiscible substrate, based on maximum substrate uptake rate. The impact of this strategy ensured that the substrate was supplied at the rate matching the maximum substrate utilization by the cells without excess feeding, leading to increased rhamnolipid production, yield and productivity.

High level production of the Magnaporthe grisea fructose 1,6-bisphosphate aldolase enzyme in Escherichia coli using a small volume bench-top fermentor

The Class II fructose 1,6-bisphosphate aldolase from the Rice Blast causative agent Magnaporthe grisea was subcloned in the Escherichia coli vector pT7-7. The enzyme was overexpressed using fed-batch fermentation in a small bench-top reactor. A total of 275 g of cells and 1.3 g of highly purified enzyme with a specific activity of 70 U/mg were obtained from a 1.5L culture. The purified enzyme is a homodimer of 39.6 kDa subunits with a zinc ion at the active site. Kinetic characterization indicates that the enzyme has a K(m) of 51 microM, a k(cat) of 46 s(-1), and a pH optimum of 7.8 for fructose 1,6-bisphosphate cleavage. The fermentation system procedure reported exemplifies the potential of using a lab-scale bioreactor for the large scale production of recombinant enzymes.

A recombinant vaccine against hydatidosis: production of the antigen in Escherichia coli

A commercial process was developed for producing a recombinant vaccine against hydatidosis in farm animals. The vaccine antigen consisting of a surface protein of the oncospheres of the hydatid worm (Echinococcus granulosus), was produced as inclusion bodies in Escherichia coli. Fed-batch cultures of E. coli using Terrific broth in stirred bioreactors at 37 degrees C, pH 7.0, and a dissolved oxygen level of 30% of air saturation produced the highest volumetric concentrations of the final solubilized antigen. An exponential feeding strategy proved distinctly superior to feeding based on pH-stat and DO-stat methods. The plasmid coding for the antigen was induced with isopropyl-beta-D-thiogalactopyranoside (IPTG) at 4 h after initiation of the culture. The minimum IPTG concentration for full induction was 0.1 mM.

The generation of high biomass from chlororespiring bacteria using a continuous fed-batch bioreactor

A continuous fed-batch reactor system was developed to rapidly obtain dense chlororespiring cultures of Anaeromyxobacter dehalogenans strain 2CP-C. A syringe pump continuously delivered concentrated 2,6-dichlorophenol (50-150 mM) to an anaerobic reactor vessel at a rate that sustained linear growth but prevented the substrate toxicity of chlorophenol. Dechlorination was not significantly inhibited by end product phenol up to 8 mM. A cell density of 76.8 mg protein l(-1) was obtained in 24 h. Specific growth rates averaged 0.033 h(-1)at 50% substrate limitation, which was in agreement with the maximum specific growth rate of 0.068 h(-1). This reactor system provides an efficient, cost-effective, and convenient method to rapidly obtain dense dechlorinating biomass and is promising to accelerate investigations of enzymes involved in chlororespiration.

Control of fed-batch fermentations

Fed-batch fermentation is used to prevent or reduce substrate-associated growth inhibition by controlling nutrient supply. Here we review the advances in control of fed-batch fermentations. Simple exponential feeding and inferential methods are examined, as are newer methods based on fuzzy control and neural networks. Considerable interest has developed in these more advanced methods that hold promise for optimizing fed-batch techniques for complex fermentation systems.

Fed-batch optimization of ?-amylase and protease-producingBacillus subtilis using Markov chain methods

A stoichiometry-based model for the fed-batch culture of the recombinant bacterium Bacillus subtilis ATCC 6051a, producing extracellular alpha-amylase as a desirable product and proteases as undesirable products, was developed and verified. The model was then used for optimizing the feeding schedule in fed-batch culture. To handle higher-order model equations (14 state variables), an optimization methodology for the dual-enzyme system is proposed by integrating Pontryagin's optimum principle with fermentation measurements. Markov chain Monte Carlo (MCMC) procedures were appropriate for model parameter and decision variable estimation by using a priori parameter distributions reflecting the experimental results. Using a simplified Metropolis-Hastings algorithm, the specific productivity of alpha-amylase was maximized and the optimum path was confirmed by experimentation. The optimization process predicted a further 14% improvement of alpha-amylase productivity that could not be realized because of the onset of sporulation. Among the decision variables, the switching time from batch to fed-batch operation (t(s)) was the most sensitive decision variable.

Biotechnological manufacture of lysine

L-Lysine has been manufactured using Corynebacterium glutamicum for more than 40 years. Nowadays production exceeds 600,000 tons per year. Based on conventionally bred strains, further improvement of lysine productivity has been achieved by genetic engineering. Pyruvate carboxylase, aspartate kinase, dihydrodipicolinate synthase, homoserine dehydrogenase and the specific lysine exporter were shown to be key enzymes for lysine production and were characterized in detail. Their combined engineering led to a striking increase in lysine formation. Pathway modeling with data emerging from 13C-isotope experiments revealed a coordinated flux through pentose phosphate cycle and tricarboxylic acid cycle and intensive futile cycling between C3 compounds of glycolysis and C4 compounds of tricarboxylic acid cycle. Process economics have been optimized by developing repeated fed-batch techniques and technical continuous fermentations. In addition, on-line metabolic pathway analysis or flow cytometry may help to improve the fermentation performance. Finally, the availability of the Corynebacterium glutamicum genome sequence has a major impact on the improvement of the biotechnological manufacture of lysine. In this context, all genes of the carbon flow from sugar uptake to lysine secretion have been identified and are accessible to manipulation. The whole sequence information gives access to post genome technologies such as transcriptome analysis, investigation of the proteome and the active metabolic network. These multi-parallel working technologies will accelerate the generation of knowledge. For the first time there is a chance of understanding the overall picture of the physiological state of lysine overproduction in a technical environment.

Modelling plasmid instability in batch and continuous fermentors

The probability of complete loss of plasmid material from plasmid bearing cells undergoing active growth has been modelled and incorporated into predictions for the dynamic concentrations of plasmid bearing cells in both batch and continuous flow, stirred tank bioreactors. The new model is based on an extension of the well-used model of Imanaka and Aiba [Ann. New York Acad. Sci. 369 (1981) 1] and is relatively easy to use compared to complex structured models. The new model predicts that both accelerating and decelerating rates of plasmid loss occur in both batch and continuous flow operation, and agrees well with data collected here and published earlier by others.