High cell density fermentation of recombinant Escherichia coli with computer-controlled optimal growth rate

Efficient Production of Lactobionic Acid Using Escherichia coli Capable of Synthesizing Pyrroloquinoline Quinone

Lactobionic acid (LBA) is an emerging chemical that has been widely utilized in food, cosmetic, and pharmaceutical industries. We sought to produce LBA using Escherichia coli. LBA can be produced from lactose in E. coli, which is innately unable to produce LBA, by coexpressing a heterologous quinoprotein glucose dehydrogenase (GDH) and a pyrroloquinoline quinone (PQQ) synthesis gene cluster. Using a recombinant E. coli strain, we successfully produced LBA without additional supplementation of PQQ, and changing the type of heterologous GDH improved the LBA production titer and productivity. To further enhance LBA production, culture conditions, such as growth temperature and isopropyl-β-d-1-thiogalactopyranoside concentration, were optimized. Using optimized culture conditions, batch fermentation of the recombinant E. coli strain was performed using a 5 L bioreactor. After fermentation, this strain produced an LBA titer of 209.3 g/L, a yield of 100%, and a productivity of 1.45 g/L/h. To our best knowledge, this is the first study to produce LBA using heterologous GDH in an E. coli strain without any additional cofactors. Our results provide a simple method to produce LBA from lactose in a naturally non-LBA-producing bacterium and lay the groundwork for highly efficient LBA production in E. coli, which is one of the most versatile metabolite-producing bacterial hosts.

Identification of a lactose-oxidizing enzyme in Escherichia coli and improvement of lactobionic acid production by recombinant expression of a quinoprotein glucose dehydrogenase from Pseudomonas taetrolens

Lactobionic acid (LBA), an aldonic acid prepared by oxidation of the free aldehyde group of lactose, has been broadly used in cosmetic, food, and pharmaceutical industries. Although Escherichia coli is unable to produce LBA naturally, a wild-type E. coli strain successfully produced LBA from lactose upon pyrroloquinoline quinone (PQQ) supplementation, indicating that E. coli contains at least one lactose-oxidizing enzyme as an apo-form. By inactivating the candidate genes in the E. coli chromosome, we found that the lactose-oxidizing enzyme of E. coli was the quinoprotein glucose dehydrogenase (GCD). To improve the LBA production ability of the E. coli strain, quinoprotein glucose dehydrogenase (GDH) from Pseudomonas taetrolens was recombinantly expressed and culture conditions such as growth temperature, initial lactose concentration, PQQ concentration, and isopropyl-β-D-1-thiogalactopyranoside induction concentration were optimized. We performed batch fermentation using a 5-L bioreactor under the optimized culture conditions determined in flask culture experiments. After batch fermentation, the LBA production titer, yield, and productivity of the recombinant E. coli strain were 200 g/L, 100 %, and 1.28 g/L/h, respectively. To the best our knowledge, this is the first report to identify the lactose-oxidizing enzyme of E. coli and to produce LBA using a recombinant E. coli strain as the production host. Because E. coli is one of the most easily genetically manipulated bacteria, our result provides the groundwork to further enhance LBA production by metabolic engineering of LBA-producing E. coli.

Efficient brazzein production in yeast (Kluyveromyces lactis) using a chemically defined medium

The sweet-tasting protein brazzein offers considerable potential as a functional sweetener with antioxidant, anti-inflammatory, and anti-allergic properties. Here, we optimized a chemically defined medium to produce secretory recombinant brazzein in Kluyveromyces lactis, with applications in mass production. Compositions of defined media were investigated for two phases of fermentation: the first phase for cell growth, and the second for maximum brazzein secretory production. Secretory brazzein expressed in the optimized defined medium exhibited higher purity than in the complex medium; purification was by ultrafiltration using a molecular weight cutoff, yielding approximately 107 mg L^-1. Moreover, the total media cost in this defined medium system was approximately 11% of that in the optimized complex medium to generate equal amounts of brazzein. Therefore, the K. lactis expression system is useful for mass-producing recombinant brazzein with high purity and yield at low production cost and indicates a promising potential for applications in the food industry.

Process development and cGMP manufacturing of a recombinant ricin vaccine: an effective and stable recombinant ricin A-chain vaccine-RVEc™

Ricin is a potent toxin and a potential bioterrorism weapon with no specific countermeasures or vaccines available. The holotoxin is composed of two polypeptide chains linked by a single disulfide bond: the A-chain (RTA), which is an N-glycosidase enzyme, and the B-chain (RTB), a lectin polypeptide that binds galactosyl moieties on the surface of the mammalian target cells. Previously (McHugh et al.), a recombinant truncated form of RTA (rRTA1-33/44-198 protein, herein denoted RVEa™) expressed in Escherichia coli using a codon-optimized gene was shown to be non-toxic, stable, and protective against a ricin challenge in mice. Here, we describe the process development and scale-up at the 12 L fermentation scale, and the current Good Manufacturing Practice (cGMP)-compliant production of RVEc™ at the 40 L scale. The average yield of the final purified bulk RVEc™ is approximately 16 g/kg of wet cell weight or 1.2 g/L of fermentation broth. The RVEc™ was >99% pure by three HPLC methods and SDS-PAGE. The intact mass and peptide mapping analysis of RVEc™ confirmed the identity of the product and is consistent with the absence of posttranslational modifications. Potency assays demonstrated that RVEc™ was immunoprotective against lethal ricin challenge and elicited neutralizing anti-ricin antibodies in 95-100% of the vaccinated mice.

Production of recombinant proteins using multiple-copy gene integration in high-cell-density fermentations of Ralstonia eutropha

We have previously reported the development of a novel protein expression system based on Ralstonia eutropha. In this study we report on the influence of gene copynumber on recombinant protein expression in R. eutropha. We compare recombinant gene stability and expression levels of chromosomal integration with a plasmid-based expression system. Single, double, and triple copies of a gene encoding organophosphohydrolase (OPH), an enzyme prone to inclusion-body formation in E. coli, were integrated into the R. eutropha chromosome. A linear increase between the concentration of soluble, active OPH and gene copynumber was found. Using a triple-copy integrant, we were able to produce approximately 4.3 g/L of OPH in a high-cell-density fermentation. This represents the highest titer reported to date for this enzyme, and is approximately 30 times greater than expression levels reported in E. coli.

Development of a versatile computer integrated control system for bioprocess controls

A general approach is described for the implementation of a networked multi-unit computer integrated control system. The use of data acquisition hardware and graphical programming tools alleviates tedious programming and maintains potency and flexibility. One application of the control system, the control of a mammalian cell perfusion culture based on a key nutrient glucose concentration, was demonstrated. The control system offers customized user interface for all process control parameters and allows the flexibility for continued improvement and implementation of new tailored functions. The temperature, pH, dissolved oxygen and glucose level were accurately controlled.