Microwave-synthesized magnetic chitosan microparticles for the immobilization of yeast cells

Synthesis and Characterization of Porous Chitosan/Saccharomycetes Adsorption Microspheres

Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres was characterized by X-ray diffraction. The results showed that the adsorption sites of amino and hydroxyl groups had been provided by the porous chitosan/saccharomycetes microspheres for the removal of preservatives, pigments, and other additives in food. The surface roughness of microspheres could be improved by increasing the mass ratio of saccharomycetes. The increase in silica gels could make the microsphere structure more compact. The porous chitosan/saccharomycetes microspheres could be used as adsorbents to adsorb doxycycline in wastewater.

Impacts of Magnetic Immobilization on the Growth and Metabolic Status of Recombinant Pichia pastoris

Downstream processing is an expensive step for industrial production of recombinant proteins. Cell immobilization is known as one of the ideal solutions in regard to process intensification. In recent years, magnetic immobilization was introduced as a new technique for cell immobilization. This technique was successfully employed to harvest many bacterial and eukaryotic cells. But there are no data about the influence of magnetic immobilization on the eukaryotic inducted recombinant cells. In this study, impacts of magnetic immobilization on the growth and metabolic status of induced recombinant Pichia pastoris as a valuable eukaryotic model cells were investigated. Results based on colony-forming unit, OD600, and trypan blue assay indicated that magnetic immobilization had no adverse effect on the growth and viability of P. pastoris cells. Also, about 20-40% increase in metabolic activity was recorded in immobilized cells that were decorated with 0.5-2 mg/mL nanoparticles. Total protein and carbohydrate of the cells were also measured as main indicatives for cell function and no significant changes were observed in the immobilized cells. Current data show magnetic immobilization as a biocompatible technique for application in eukaryotic expression systems. Results can be considered for further developments in P. pastoris-based expression systems.

Carbon nanomaterial properties help to enhance xylanase production from recombinant Kluyveromyces lactis through a cell immobilization method

Carbon nanomaterials, due to their catalytic activity and high surface area, have potential as cell immobilization supports to increase the production of xylanase. Recombinant Kluyveromyces lactis used for xylanase production was integrated into a polymeric gel network with carbon nanomaterials. Carbon nanomaterials were pretreated before cell immobilization with hydrochloric acid (HCl) treatment and glutaraldehyde (GA) crosslinking, which contributes to cell immobilization performance. Carbon nanotubes (CNTs) and graphene oxide (GO) were further screened using a Plackett-Burman experimental design. Cell loading and agar concentration were the most important factors in xylanase production with low cell leakage. Under optimized conditions, xylanase production was increased by more than 400% compared to free cells. Immobilized cell material containing such high cell densities may exhibit new and unexplored beneficial properties because the cells comprise a large fraction of the component. The use of carbon nanomaterials as a cell immobilization support along with the entrapment method successfully enhances the production of xylanase, providing a new route to improved bioprocessing, particularly for the production of enzymes. KEY POINTS: • Carbon nanomaterials (CNTs, GO) have potential as cell immobilization supports. • Entrapment in a polymeric gel network provides space for xylanase production. • Plackett-Burman design screen for the most important factor for cell immobilization.

Impacts of Magnetic Immobilization on the Recombinant Proteins Structure Produced in Pichia pastoris System

Pichia pastoris expression system was introduced with post-translation process similar to higher eukaryotes. Preliminary studies were performed toward process intensification and magnetic immobilization of this system. In this experiment, effects of magnetic immobilization on the structure of recombinant protein were evaluated. P. pastoris cell which express human serum albumin (HSA) was used as a model. The cells were immobilized with various concentrations of APTES coated magnetite nanoparticles. HSA production was done over 5 days induction and structure of the product was analyzed by UV-vis, fluorescence, and ATR-FTIR spectroscopy. Second derivative deconvolution method was used to analyze the secondary structure of HSA. P. pastoris cell that were immobilized with 0.5 and 1 mg/mL of nanoparticles were produced HSA with intact structure. But immobilization with 2 mg/mL of nanoparticles resulted in some modifications in the secondary structures (i.e., α-helixes and β-turns) of produced HSA. Based on these data, immobilization of P. pastoris cells with 0.5 or 1 mg/mL of nanoparticles is completely efficient for cell harvesting and has any effect on the structure of recombinant product. These findings revealed that decoration of microbial cells with high concentrations of nanoparticles has some impacts on the structure of secretory proteins.

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.

Magnetization of active inclusion bodies: comparison with centrifugation in repetitive biotransformations

Background

Physiological aggregation of a recombinant enzyme into enzymatically active inclusion bodies could be an excellent strategy to obtain immobilized enzymes for industrial biotransformation processes. However, it is not convenient to recycle “gelatinous masses” of protein inclusion bodies from one reaction cycle to another, as high centrifugation forces are needed in large volumes. The magnetization of inclusion bodies is a smart solution for large-scale applications, enabling an easier separation process using a magnetic field.

Results

Magnetically modified inclusion bodies of UDP–glucose pyrophosphorylase were recycled 50 times, in comparison, inclusion bodies of the same enzyme were inactivated during ten reaction cycles if they were recycled by centrifugation. Inclusion bodies of sialic acid aldolase also showed good performance and operational stability after the magnetization procedure.

Conclusions

It is demonstrated here that inclusion bodies can be easily magnetically modified by magnetic iron oxide particles prepared by microwave-assisted synthesis from ferrous sulphate. The magnetic particles stabilize the repetitive use of the inclusion bodies .

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0987-7) contains supplementary material, which is available to authorized users.