The methylotrophic yeast as a host for the expression and production of thermostable xylanase from the bacterium

Lyophilized yeast powder for adjuvant free thermostable vaccine delivery

Thermolabile nature of commercially available vaccines necessitates their storage, transportation, and dissemination under refrigerated condition. Maintenance of continuous cold chain at every step increases the final cost of vaccines. Any breach in the cold chain even for a short duration results in the need to discard the vaccines. As a result, there is a pressing need for the development of thermostable vaccines. In this proof-of-concept study, we showed that E. coli curli-green fluorescent fusion protein remains stable in freeze-dried yeast powder for more than 18 and 12 months when stored at 30 °C and 37 °C respectively. Stability of the heterologous protein remains unaffected during the process of heat-inactivation and lyophilization. The mass of lyophilized yeast powder remains almost unchanged during the entire period of storage and expressed protein remains intact even after two cycles of freeze and thaws. The protease-deficient strain appears ideal for the development of whole recombinant yeast-based vaccines. The cellular abundance of expressed antigen in dry powder after a year was comparable to freshly lyophilized cells. Scanning electron microscopy showed the intact nature of cells in powdered form even after a year of storage at 30 °C. Observation made in this study showed that freeze-dry yeast powder can play a vital role in the development of thermostable vaccines.

Key Points

• Yeast-based vaccines can overcome problem of cold chain associated with conventional vaccines

• Lyophilized yeast powder can be a simple way for long-term storage of immunogen(s)

• Protease deficient strain is important for whole recombinant yeast-based vaccines

Production, characteristics, and biotechnological applications of microbial xylanases

Microbial xylanases have gathered great attention due to their biotechnological potential at industrial scale for many processes. A variety of lignocellulosic materials, such as sugarcane bagasse, rice straw, rice bran, wheat straw, wheat bran, corn cob, and ragi bran, are used for xylanase production which also solved the great issue of solid waste management. Both solid-state and submerged fermentation have been used for xylanase production controlled by various physical and nutritional parameters. Majority of xylanases have optimum pH in the range of 4.0-9.0 with optimum temperature at 30-60 °C. For biochemical, molecular studies and also for successful application in industries, purification and characterization of xylanase have been carried out using various appropriate techniques. Cloning and genetic engineering are used for commercial-level production of xylanase, to meet specific economic viability and industrial needs. Microbial xylanases are used in various biotechnological applications like biofuel production, pulp and paper industry, baking and brewing industry, food and feed industry, and deinking of waste paper. This review describes production, characteristics, and biotechnological applications of microbial xylanases.

Thermostable multifunctional GH74 xyloglucanase from Myceliophthora thermophila: high-level expression in Pichia pastoris and characterization of the recombinant protein

A xyloglucanase of the GH74 family was identified in the thermophilic fungus strain Myceliophthora thermophila VKPM F-244, and its gene sequence was optimized for cloning and expression in Pichia pastoris. The recombinant xyloglucanase MtXgh74 exhibited the highest activity toward tamarind seed xyloglucan with a K _M value of 0.51 ± 0.06 mg/mL. The activities on barley β-glucan and carboxymethylcellulose were about 4 and 2%, respectively, compared to xyloglucan. Maximum xyloglucanase activity was observed at 70-75 °C and pH 6.5. After pre-incubation at 50 °C, pH 6.0 for 3 h, the enzyme retained 100% of its activity. The half-life of MtXgh74 at 60 °C, pH 6.0 was 40 min. In P. pastoris, MtXgh74 was produced in glycosylated form. The enzyme production in a 1 L bioreactor resulted in a yield of 118 U/mL or 5.3 g/L after 51 h fermentation. Kinetic studies of the hydrolysis product formation suggest that MtXgh74 has an endo-processive mode of action. The final products were the standard xyloglucan building blocks XXXG, XXLG, XLXG, and XLLG. Additionally, MtXgh74 hydrolyzed various linkages within the xyloglucan building blocks XXXG, XXLG, and XLXG (except XLLG) producing diverse low molecular weight oligosaccharides which may be identified by MALDI-TOF as XG, XX, XXG/GXX/XGX, XXX, LG, LX/XL, XLX/XXL, LLG, GXXXG, GXLLG, XLLGX. The unique combination of different activities within one enzyme along with its high thermostability and specificity toward xyloglucan makes MtXgh74 a promising candidate enzyme for industrial applications.

Disruption of KEX1 gene reduces the proteolytic degradation of secreted two-chain Insulin glargine in Pichia pastoris

Insulin glargine is a slow acting analog of insulin used in diabetes therapy. It is produced by recombinant DNA technology in different hosts namely E. coli and Pichia pastoris. In our previous study, we have described the secretion of fully folded two-chain Insulin glargine into the medium by over-expression of Kex2 protease. The enhanced levels of the Kex2 protease was responsible for the processing of the glargine precursor with in the host. Apart from the two-chain glargine product we observed a small proportion of arginine clipped species. This might be due to the clipping of arginine present at the C-terminus of the B-chain as it is exposed upon Kex2 cleavage. The carboxypeptidase precursor Kex1 is known to be responsible for clipping of C-terminal lysine or arginine of the proteins or peptides. In order to address this issue we created a Kex1 knock out in the host using Cre/loxP mechanism of targeted gene deletion. When two-chain glargine was expressed in the Kex1 knock out host of P. pastoris GS115 the C-terminal clipped species reduced by ∼80%. This modification further improved the process by reducing the levels of product related impurities.

A newly isolated yeast as an expression host for recombinant lipase

Pichia guilliermondii strain SO isolated from spoiled orange was developed for use as an alternative expression host by using Pichia pastoris as the model of the experiment. This is the first study to report on the capability of P. guilliermondii SO as a host to express thermostable T1 lipase from Geobacillus zalihae. Alcohol oxidase and formaldehyde dehydrogenase promoters were present in the yeast genome. Interestingly, the recombinant yeast [SO/pPICZαB/T1-2 (SO2)] took only 30 h to reach optimal production with minimal methanol induction [1.5% (v/v)] in YPTM medium, as compared to P. pastoris, which took longer to reach its optimal condition. The purification yield of the His-tagged fusion lipase was 68.58%, with specific activity of 194.58 U/mg. The optimum temperature was 65°C at pH 9 in glycine-NaOH buffer, and it was stable up to 70°C in a wide pH range from pH 5 to 12. In conclusion, a newly isolated yeast from spoiled orange has been proven suitable for use as an expression host.

Expression and Characterization of Geobacillus stearothermophilus SR74 Recombinant α-Amylase in Pichia pastoris

Geobacillus stearothermophilus SR74 is a locally isolated thermophilic bacteria producing thermostable and thermoactive α-amylase. Increased production and commercialization of thermostable α-amylase strongly warrant the need of a suitable expression system. In this study, the gene encoding the thermostable α-amylase in G. stearothermophilus SR74 was amplified, sequenced, and subcloned into P. pastoris GS115 strain under the control of a methanol inducible promoter, alcohol oxidase (AOX). Methanol induced recombinant expression and secretion of the protein resulted in high levels of extracellular amylase production. YPTM medium supplemented with methanol (1% v/v) was the best medium and once optimized, the maximum recombinant α-amylase SR74 achieved in shake flask was 28.6 U mL(-1) at 120 h after induction. The recombinant 59 kDa α-amylase SR74 was purified 1.9-fold using affinity chromatography with a product yield of 52.6% and a specific activity of 151.8 U mg(-1). The optimum pH of α-amylase SR74 was 7.0 and the enzyme was stable between pH 6.0-8.0. The purified enzyme was thermostable and thermoactive, exhibiting maximum activity at 65°C with a half-life (t₁/₂) of 88 min at 60°C. In conclusion, thermostable α-amylase SR74 from G. stearothermophilus SR74 would be beneficial for industrial applications, especially in liquefying saccrification.

Functional analysis of a lipolytic protein encoded in phytoplasma phage based genomic island

Wall-less bacteria known as phytoplasmas are obligate transkingdom parasites and pathogens of plants and insect vectors. These unusual bacteria possess some of the smallest genomes known among pathogenic bacteria, and have never been successfully isolated in artificial culture. Disease symptoms induced by phytoplasmas in infected plants include abnormal growth and often severe yellowing of leaves, but mechanisms involved in phytoplasma parasitism and pathogenicity are little understood. A phage based genomic island (sequence variable mosaic, SVM) in the genome of Malaysian periwinkle yellows (MPY) phytoplasma harbors a gene encoding membrane-targeted proteins, including a putative phospholipase (PL), potentially important in pathogen-host interactions. Since some phytoplasmal disease symptoms could possibly be accounted for, at least in part, by damage and/or degradation of host cell membranes, we hypothesize that the MPY phytoplasma putative PL is an active enzyme. To test this hypothesis, functional analysis of the MPY putative pl gene-encoded protein was carried out in vitro after its expression in bacterial and yeast hosts. The results demonstrated that the heterologously expressed phytoplasmal putative PL is an active lipolytic enzyme and could possibly act as a pathogenicity factor in the plant, and/or insect, host.

High expression of recombinant Streptomyces sp. S38 xylanase in Pichia pastoris by codon optimization and analysis of its biochemical properties

In recent years, the biotechnological use of xylanases has grown remarkably. To efficiently produce xylanase for food processing and other industry, a codon-optimized recombinant xylanase gene from Streptomyces sp. S38 was synthesized and extracellularly expressed in Pichia pastoris under the control of AOX1 promoter. SDS-PAGE and activity assay demonstrated that the molecular mass of the recombinant xylanase was estimated to be 25 kDa, the optimum pH and optimum temperature were 5.5 and 50°C, respectively. In shake flask culture, the specific activity of the xylanase activity was 5098.28 U/mg. The K ( m ) and V ( max ) values of recombinant xylanase were 11.0 mg/ml and 10000 μmol min(-1) mg(-1), respectively. In the presence of metal ions such as Ca(2+), Cu(2+), Cr(3+) and K(+), the activity of the enzyme increased. However, strong inhibition of the enzyme activity was observed in the presence of Hg(2+). This is the first report on the expression properties of a recombinant xylanase gene from the Streptomyces sp. S38 using Pichia pastoris. The attractive biochemical properties of the recombinant xylanase suggest that it may be a useful candidate for variety of commercial applications.

Fed-batch methanol feeding strategy for recombinant protein production by Pichia pastoris in the presence of co-substrate sorbitol

Batch-wise sorbitol addition as a co-substrate at the induction phase of methanol fed-batch fermentation by Pichia pastoris (Mut(+)) was proposed as a beneficial recombinant protein production strategy and the metabolic responses to methanol feeding rate in the presence of sorbitol was systematically investigated. Adding sorbitol batch-wise to the medium provided the following advantages over growth on methanol alone: (a) eliminating the long lag-phase for the cells and reaching 'high cell density production' at t = 24 h of the process (C(X) = 70 g CDW/l); (b) achieving 1.8-fold higher recombinant human erythropoietin (rHuEPO) (at t = 18 h); (c) reducing specific protease production 1.2-fold; (d) eliminating the lactic acid build-up period; (e) lowering the oxygen uptake rate two-fold; and (f) obtaining 1.4-fold higher overall yield coefficients. The maximum specific alcohol oxidase activity was not affected in the presence of sorbitol, and it was observed that sorbitol and methanol were utilized simultaneously. Thus, in the presence of sorbitol, 130 mg/l rHuEPO was produced at t = 24 h, compared to 80 mg/l rHuEPO (t = 24 h) on methanol alone. This work demonstrates not only the ease and efficiency of incorporating sorbitol to fermentations by Mut(+) strains of P. pastoris for the production of any bio-product, but also provides new insights into the metabolism of the methylotrophic yeast P. pastoris.

Inflammatory Thermophilic Fungi are Used in Biotechnology Applications

Thermophilic microorganisms which can colonize at extreme ecological niches are known as extremophiles. Because of their capacity to withstand high temperatures, enzymes from these organisms are relatively heat stable. The versatile enzyme properties of these organisms make them excellent candidates in biotechnology. In general, fungi have been widely used for the production of proteins and enzymes, since they can grow rapidly in a low cost media and they secrete proteins into the extra-cellular medium. Recently, these organisms have also been used in large scale fermentation as host for the expression of heterologous proteins in industrial applications. However, little is known about the regulation and genetic manipulations of these fungi. We have previously shown the regulation of gene expression in a thermophilic fungus, Thermyces lanuginosus, using an inducible invertase system. The aim of this review is to elucidate the recent advances of thermophilic fungi, and their implications in industrial applications are discussed.

Expression of recombinant Aspergillus niger xylanase A in Pichia pastoris and its action on xylan

The mature peptide of Aspergillus niger xylanase A (AnxA) was successfully expressed in Pichia pastoris at high levels under the control of AOX1 promoter. The recombinant AnxA (reAnxA) was secreted into culture medium. After 96-h 0.25% methanol induction, the activity of reAnxA in the culture supernatant reached the peak, 175 U/mg, which was 1.9 times as high as that of the native AnxA (92 U/mg). Studies on enzymatic properties showed that the optimum temperature and optimum pH of reAnxA were 50 degrees C and 5.0, respectively. The reAnxA was very stable in a wide pH range of 3.0-8.0. After incubation at the pH 3.0-8.0, 25 degrees C for 1h, all the residual activities of reAnxA were over 80%. The K(m) and k(cat) values for reAnxA were 4.8 mg/ml and 123.2s(-1), respectively. HPLC analysis showed that xylotriose was the main hydrolysis product of birchwood xylan and bran insoluble xylan by reAnxA.

Production of a lipolytic enzyme originating from Bacillus halodurans LBB2 in the methylotrophic yeast Pichia pastoris

A gene encoding a lipolytic enzyme amplified from the alkaliphilic bacterium Bacillus halodurans LBB2 was cloned into the pPICZalphaB vector and integrated into the genome of the protease deficient yeast strain Pichia pastoris SMD1168H. This previously undescribed enzyme was produced in active form, and cloning in frame with the Saccharomyces cerevisiae secretion signal (alpha-factor) enabled extracellular accumulation of correctly processed enzyme, with an apparent molecular mass of 30 kDa. In shake-flask cultivations, very low production levels were obtained, but these were significantly improved by use of a "batch-induced" cultivation technique which allowed a maximum enzyme activity of 14,000 U/l using p-nitrophenyl butyrate (C-4) as a substrate and a final extracellular lipolytic enzyme concentration of approximately 0.2 g/l. Partial characterization of the produced enzyme (at pH 9) revealed a preference for the short-chain ester (C-4) and significant but lower activity towards medium (C5-C6) and long (C16 and C18) fatty acid chain-length esters. In addition, the enzyme exhibited true lipase activity (7,300 U/l) using olive oil as substrate and significant levels of phospholipase activity (6,400 U/l) by use of a phosphatidylcholine substrate, but no lysophospholipase activity was detected using a lysophosphatidylcholine substrate.