Magnetic Immobilization of Pichia pastoris Cells for the Production of Recombinant Human Serum Albumin

Magnetic immobilization as a novel technique was used to immobilize recombinant Pichia pastoris (GS115 Albumin) cells to produce human serum albumin (HSA). In this regard, magnetic nanoparticles (MNPs) coated with amino propyl triethoxy silane (APTES) were synthesized. P. pastoris cells were decorated with MNPs via nonspecific interactions. Decorated cells were magneto-responsible and easily harvested by applying an external magnetic field. The efficiency of magnetic immobilization (E_i) for cell removal was in direct relation with the MNP concentration and time of exposure to the magnetic field. By increasing the nanoparticles concentration, cells were harvested in a shorter period. Complete cell removal (E_i ≈ 100) was achieved in ≥0.5 mg/mL of MNPs in just 30 s. HSA is produced in an extremely high cell density (OD ~20) and it is the first time that magnetic immobilization was successfully employed for harvesting such a thick cell suspension. After 5 days of induction the cells, which were immobilized with 0.25 to 1 mg/mL of nanoparticles, showed an increased potency for recombinant HSA production. The largest increase in HSA production (38.1%) was achieved in the cells that were immobilized with 0.5 mg/mL of nanoparticles. These results can be considered as a novel approach for further developments in the P. pastoris-based system.

Synthesis and characterization of Ogataea thermomethanolica alcohol oxidase immobilized on barium ferrite magnetic microparticles

Alcohol oxidase catalyzes the oxidation of primary alcohols into the corresponding aldehydes, making it a potential biocatalyst in the chemical industry. However, the high production cost and poor operational stability of this enzyme are limitations for industrial application. Immobilization of enzyme onto solid supports is a useful strategy for improving enzyme stability. In this work, alcohol oxidase from the thermotolerant methylotrophic yeast Ogataea thermomethanolica (OthAOX) was covalently immobilized onto barium ferrite (BaFe₁₂O₁₉) magnetic microparticles. Among different conditions tested, the highest immobilization efficiency of 71.0 % and catalytic activity of 34.6 U/g was obtained. Immobilization of OthAOX onto magnetic support was shown by Fourier-Transformed infrared microscopy, scanning electron microscopy and X-ray diffraction. The immobilized OthAOX worked optimally at 55 °C and pH 8.0. Immobilization also improved thermostability, in which >65% of the initial immobilized enzyme activity was retained after 24 h pre-incubation at 45 °C. The immobilized enzyme showed a greater catalytic efficiency for oxidation of methanol and ethanol than free enzyme. The immobilized enzyme could be recovered by magnetization and recycled for at least three consecutive batches, after which 70% activity remained. The properties of the immobilized enzyme suggest its potential industrial application for synthesis of aldehyde.

Comparative analysis of stirred catalytic basket bio-reactor for the production of bio-ethanol using free and immobilized Saccharomyces cerevisiae cells

The successful industrial production of ethanol and fine chemicals requires the development of new biocatalytic reactors and support materials to achieve economically viable processes. In this work, a Stirred-Catalytic-Basket-BioReactor using various immobilizing foams as support material and compared to free cells were used, focusing mainly on; (i) effect of mass-transfer on cells physiology and (ii) ethanol productivity. The performance of the reactor was further evaluated by ethanol volumetric productivity, yield and time for process completion and it was found that the variation of ethanol production and diffusion of the substrate in fermentation process are co-related with the stirrer speed and initial glucose concentration. It was also observed that the time difference for glucose consumption between free and immobilized cells (alginate and sponges) tends to increase by increasing the glucose concentration in the medium. We found that at higher stirrer speed (500 rpm) when using higher glucose concentration (200 g/l), ethanol volumetric productivity increased significantly in the sponge (85 g/l) as compared to alginate beads (79 g/l) and free cells (60 g/l). From the data obtained, it can be concluded that sponges are the best support material for attaining higher ethanol productivity. A stirred catalytic basket bioreactor with yeast cells immobilized in polyethylene sponge gives higher ethanol production at a higher glucose consumption rate, and this productivity is due to higher mixing efficiency and reduced external as well as internal mass transfer limitations. The potentials of the reactor rank it as a remarkable ethanol/fine-chemical production approach that needs further investigations.

Agitation rate effects on plasmid stability in immobilized and free-cell continuous cultures of recombinant E. coli

Escherichia coli B/pTG201 recombinant cells were immobilized by entrapment in a carrageenan gel and cultivated in nonselective media to investigate the effect of agitation rate on plasmid stability, biomass concentration, and enzyme productivity. These parameters were studied in continuous cultures for free and immobilized cells, respectively. Immobilized recombinant cells exhibit an increase in the stability of the plasmid pTG201 compared to free cells, even under conditions where the tendency of plasmid stability for free cells decreased generally more rapidly under a higher agitation rate. Intensive agitation, resulting also in a strong shear stress, greatly reduced cell concentration within gel beads throughout the course of growth. Higher enzyme expression of catechol 2-3, dioxygenase was also obtained in leaked cells due to better maintenance of plasmid stability and higher plasmid copy number with regard to free cells. Enzyme productivity of leaked and free cells in minimal medium decreased with the increase in agitation rate, due to decreased plasmid stability; however, in LB medium, it increased in the presence of higher agitation rate related to important cell concentration.