Improved Production of Aspergillus usamii endo-β-1,4-Xylanase in Pichia pastoris via Combined Strategies

Recent Advances in the Physicochemical Properties and Biotechnological Application of Vitreoscilla Hemoglobin

Vitreoscilla hemoglobin (VHb), the first discovered bacterial hemoglobin, is a soluble heme-binding protein with a faster rate of oxygen dissociation. Since it can enhance cell growth, product synthesis and stress tolerance, VHb has been widely applied in the field of metabolic engineering for microorganisms, plants, and animals. Especially under oxygen-limited conditions, VHb can interact with terminal oxidase to deliver enough oxygen to achieve high-cell-density fermentation. In recent years, with the development of bioinformatics and synthetic biology, several novel physicochemical properties and metabolic regulatory effects of VHb have been discovered and numerous strategies have been utilized to enhance the expression level of VHb in various hosts, which greatly promotes its applications in biotechnology. Thus, in this review, the new information regarding structure, function and expressional tactics for VHb is summarized to understand its latest applications and pave a new way for the future improvement of biosynthesis for other products.

Single-Cell Approach to Monitor the Unfolded Protein Response During Biotechnological Processes With Pichia pastoris

Pichia pastoris (Komagataella sp.) is broadly used for the production of secreted recombinant proteins. Due to the high rate of protein production, incorrectly folded proteins may accumulate in the endoplasmic reticulum (ER). To restore their proper folding, the cell triggers the unfolded protein response (UPR); however, if the proteins cannot be repaired, they are degraded, which impairs process productivity. Moreover, a non-producing/non-secreting subpopulation of cells might occur, which also decreases overall productivity. Therefore, an in depth understanding of intracellular protein fluxes and population heterogeneity is needed to improve productivity. Under industrially relevant cultivation conditions in bioreactors, we cultured P. pastoris strains producing three different recombinant proteins: penicillin G acylase from Escherichia coli (EcPGA), lipase B from Candida antarctica (CaLB) and xylanase A from Thermomyces lanuginosus (TlXynA). Extracellular and intracellular product concentrations were determined, along with flow cytometry-based single-cell measurements of cell viability and the up-regulation of UPR. The cell population was distributed into four clusters, two of which were viable cells with no UPR up-regulation, differing in cell size and complexity. The other two clusters were cells with impaired viability, and cells with up-regulated UPR. Over the time course of cultivation, the distribution of the population into these four clusters changed. After 30 h of production, 60% of the cells producing EcPGA, which accumulated in the cells (50-70% of the product), had up-regulated UPR, but only 13% of the cells had impaired viability. A higher proportion of cells with decreased viability was observed in strains producing CaLB (20%) and TlXynA (27%). The proportion of cells with up-regulated UPR in CaLB-producing (35%) and TlXynA-producing (30%) strains was lower in comparison to the EcPGA-producing strain, and a smaller proportion of CaLB and TlXynA (<10%) accumulated in the cells. These data provide an insight into the development of heterogeneity in a recombinant P. pastoris population during a biotechnological process. A deeper understanding of the relationship between protein production/secretion and the regulation of the UPR might be utilized in bioprocess control and optimization with respect to secretion and population heterogeneity.

High-level expression of Thermomyces dupontii thermophilic lipase in Pichia pastoris via combined strategies

In this study, a combined strategy was used to improve the production of Thermomyces dupontii lipase (TDL) in Pichia pastoris. First, the native gene of TDL was optimized based on the codon usage of P. pastoris, ligated to pPICZαA and transformed in P. pastoris X33. A recombinant strain designated X33-T23 with the highest activity (1020 U/mL in shake flasks) amongst 216 recombinant colonies was selected for further investigations. To further increase the production of TDL, nine different secretion helper factor genes were transformed in the recombinant strain, X33-T23. The recombinant strain co-expression with the gene encoding protein disulfide isomerase, designated X33-T23-PDI, exhibited the highest activity in shake flasks (1760 U/mL) and in 5 L bioreactor (57521 U/mL) which were 1.67- and 1.46-fold higher, respectively, than for strain X33-T23. Additionally, the optimization of the inducers (temperature and pH) for the recombinant strain X33-T23-PDI in 5 L bioreactor produced, as expected, much higher lipase activity (81203 U/mL). The results of this study will provide an effective method to produce TDL and give some clues on how to improve production of heterologous proteins in P. pastoris.

Increase in the Production of Endo-1,4-β-Xylanase from Paenibacillus brasilensis in Pichia pastoris

A Pichia pastoris yeast strain producing endo-l,4-β-xylanase from Paenibacillus brasilensis with an activity of 54,400 U/mL after 140 h of fermentation in a laboratory fermenter has been obtained. A number of approaches were used to increase the level of the xylanase production in this strain: optimization of the target gene codon composition, multiple integration of the expression cassette into the recipient strain chromosome using the Cre-lox recombination system, and also improving the heterologous protein folding via the overexpression of the HAC1i gene from Pichia pastoris. xylanase, xylan, Cre-lox system, HAC1p transcriptional activator, multicopy strain, Paenibacillus brasilensis, Pichia pastoris The work was performed with the financial support of the Ministry of Education and Science of Russia (Unique Project Identifier RFMEFI60717X0180) using the Multipurpose Scientific Installation of «All-Russian Collection of Industrial Microorganisms» National Bio-Resource Center, NRC «Kurchatov Institute» - GosNIIgenetika.

Characterization of Two Endo-β-1, 4-Xylanases from Myceliophthora thermophila and Their Saccharification Efficiencies, Synergistic with Commercial Cellulase

The xylanases with high specific activity and resistance to harsh conditions are of high practical value for biomass utilization. In the present study, two new GH11 xylanase genes, MYCTH_56237 and MYCTH_49824, have been cloned from thermophilic fungus Myceliophthora thermophila and expressed in Pichia pastoris. The specific activities of purified xylanases reach approximately 1,533.7 and 1,412.5 U/mg, respectively. Based on multiple template-based homology modeling, the structures of their catalytic domains are predicted. Enzyme activity was more effective in 7.5 L fermentor, yielding 2,010.4 and 2,004.2 U/mL, respectively. Both enzymes exhibit optimal activity at 60°C with pH of 6.0 and 7.0, respectively. Their activities are not affected by EDTA and an array of metal ions. The kinetic constants have been determined for MYCTH_56237 (K_m = 8.80 mg/mL, V_max = 2,380 U/mg) and MYCTH_49824 (K_m = 5.67 mg/mL, V_max = 1,750 U/mg). More importantly, both xylanases significantly cooperate with the commercial cellulase Celluclast 1.5 L in terms of the saccharification efficiency. All these biochemical properties of the xylanases offer practical potential for future applications.

Enhancement of thermoalkaliphilic xylanase production by Pichia pastoris through novel fed-batch strategy in high cell-density fermentation

BACKGROUND

Xylanase degrades xylan into monomers of various sizes by catalyzing the endohydrolysis of the 1,4-β-D-xylosidic linkage randomly, possessing potential in wide industrial applications. Most of xylanases are susceptible to be inactive when suffering high temperature and high alkaline process. Therefore, it is necessary to develop a high amount of effective thermoalkaliphilic xylanases. This study aims to enhance thermoalkaliphilic xylanase production in Pichia pastoris through fermentation parameters optimization and novel efficient fed-batch strategy in high cell-density fermentation.

RESULTS

Recombinant xylanase activity increased 12.2%, 7.4%, 12.0% and 9.9% by supplementing the Pichia pastoris culture with 20 g/L wheat bran, 5 mg/L L-histidine, 10 mg/L L-tryptophan and 10 mg/L L-methionine in shake flasks, respectively. Investigation of nutritional fermentation parameters, non-nutritional fermentation parameters and feeding strategies in 1 L bioreactor and 1 L shake flask revealed that glycerol and methanol feeding strategies were the critical factors for high cell density and xylanase activity. In 50 L bioreactor, a novel glycerol feeding strategy and a four-stage methanol feeding strategy with a stepwise increase in feeding rate were developed to enhance recombinant xylanase production. In the initial 72 h of methanol induction, the linear dependence of xylanase activity on methanol intake was observed (R² = 0.9726). The maximum xylanase activity was predicted to be 591.2 U/mL, while the actual maximum xylanase activity was 560.7 U/mL, which was 7.05 times of that in shake flask. Recombinant xylanase retained 82.5% of its initial activity after pre-incubation at 80 °C for 50 min (pH 8.0), and it exhibited excellent stability in the broad temperature (60-80 °C) and pH (pH 8.0-11.0) ranges.

CONCLUSIONS

Efficient glycerol and methanol fed-batch strategies resulting in desired cell density and xylanase activity should be applied in other P. pastoris fermentation for other recombinant proteins production. Recombinant xylanases with high pH- and thermal-stability showed potential in various industrial applications.