Extracellular expression of a thermostable phytase (phyA) in Kluyveromyces lactis

Microbial Phytases: Properties and Applications in the Food Industry

Microbial phytases are enzymes that break down phytic acid, an anti-nutritional compound found in plant-based foods. These enzymes which are derived from bacteria and fungi have diverse properties and can function under different pH and temperature conditions. Their ability to convert phytic acid into inositol and inorganic phosphate makes them valuable in food processing. The application of microbial phytases in the food industry has several advantages. Firstly, adding them to animal feedstuff improves phosphorus availability, leading to improved nutrient utilization and growth in animals. This also reduces environmental pollution by phosphorus from animal waste. Secondly, microbial phytases enhance mineral bioavailability and nutrient assimilation in plant-based food products, counteracting the negative effects of phytic acid on human health. They can also improve the taste and functional properties of food and release bioactive compounds that have beneficial health effects. To effectively use microbial phytases in the food industry, factors like enzyme production, purification, and immobilization techniques are important. Genetic engineering and protein engineering have enabled the development of phytases with improved properties such as enhanced stability, substrate specificity, and resistance to degradation. This review provides an overview of the properties and function of phytases, the microbial strains that produce them, and their industrial applications, focusing on new approaches.

Thermostability enhancement of Escherichia coli phytase by error-prone polymerase chain reaction (epPCR) and site-directed mutagenesis

Phytase efficiently hydrolyzes phytate to phosphate; thus, it is widely used to increase phosphorus availability in animal feeds and reduce phosphorus pollution through excretion. Phytase is easily inactivated during feed pelleting at high temperature, and sufficient thermostability of phytase is essential for industrial applications. In this study, directed evolution was performed to enhance phytase thermostability. Variants were initially expressed in Escherichia coli BL21 for screening, then in Pichia pastoris for characterization. Over 19,000 clones were generated from an error-prone Polymerase Chain Reaction (epPCR) library; 5 mutants (G10, D7, E3, F8, and F9) were obtained with approximately 9.6%, 10.6%, 11.5%, 11.6%, and 12.2% higher residual activities than the parent after treatment at 99°C for 60 min. Three of these mutants, D7, E3, and F8, exhibited 79.8%, 73.2%, and 92.6% increases in catalytic efficiency (kcat/Km), respectively. In addition, the specific activities of D7, E3, and F8 were 2.33-, 1.98-, and 2.02-fold higher than parental phytase; they were also higher than the activities of all known thermostable phytases. Sequence analysis revealed that all mutants were substituted at residue 75 and was confirmed that the substitution of cysteine at position 75 was the main contribution to the improvement of thermostability of mutants by saturation mutagenesis, indicating that this amino acid is crucial for the stability and catalytic efficiency of phytase. Docking structure analysis revealed that substitution of the C75 residue allowed the mutants to form additional hydrogen bonds in the active pocket, thereby facilitating binding to the substrate. In addition, we confirmed that the intrinsic C77-C108 disulfide bond in E. coli phytase is detrimental to its stability.

Fungal phytases: from genes to applications

Phytic acid stores 60-90% of the inorganic phosphorus in legumes, oil seeds, and cereals, making it inaccessible for metabolic processes in living systems. In addition, given its negative charge, phytic acid complexes with divalent cations, starch, and proteins. Inorganic phosphorous can be released from phytic acid upon the action of phytases. Phytases are phosphatases produced by animals, plants, and microorganisms, notably Aspergillus niger, and are employed as animal feed additive, in chemical industry and for ethanol production. Given the industrial relevance of phytases produced by filamentous fungi, this work discusses the functional characterization of fungal phytase-coding genes/proteins, highlighting the physicochemical parameters that govern the enzymatic activity, the development of phytase super-producing strains, and key features for industrial applications.

Engineering and optimization of phosphate-responsive phytase expression in Pichia pastoris yeast for phytate hydrolysis

Phytate is the major storage form of phosphorus in plants. It is present in cereals and raw materials of vegetable origin used in animal and human diets. However, non-ruminant animals have little phytase activity in their guts and, therefore, cannot digest phytate. As a result, almost all dietary phytate is discharged into the environment, causing phosphorus pollution. Phytate is also considered as an "antinutrient" for its ability to form insoluble and stable complexes with metal ions, thus reducing dietary absorption of essential minerals. It is a dire need to develop sustainable approaches for environmentally-friendly utilization for this valuable and abundant natural resource. To this end, we engineered Pichia pastoris to express and secrete phytase in a "made-to-order" fashion in response to external level of inorganic phosphate (Pi). Responsiveness to external Pi level was achieved by generating a Pi-responsive promoter library using directed evolution. The resultant yeast strains were proven to liberate Pi from wheat-based meal in a simulated in vitro digestion model. These yeast-based whole cell biocatalysts may serve as platform hosts with potential applications in food processing industry and animal waste treatment.

Production of Fungal Phytases from Agroindustrial Byproducts for Pig Diets

The application of phytases for animal feed in developing countries is limited due to the high cost of these enzymes, determined by the importation fees and the expensive substrates used for their production. In this work, we have used agroindustrial byproducts for the production of extracts containing phytases, which were accessed for their stability focusing on the conditions found in the gastrointestinal tract of pigs. The fungus Acremonim zeae presented higher phytase production in medium containing cornmeal, while the yeast Kluyveromyces marxianus produced 10-fold more phytase when cultivated on rice bran. Process optimization increased the difference in productivity to more than 300 fold. The phytase from A. zeae was thermostable, with higher activity at neutral pH and 50 °C, but was inhibited at pH 2.5 and by various ions. The phytase activity in the K. marxianus extract was stable at a wide range of conditions, which indicates the presence of at least two enzymes. As far as we know, this manuscript describes for the first time the phytase production and the characteristics of the extracts produced by both these microbial species. These enzymes could be produced at low cost and have potential to replace enzymes currently imported for this purpose.

Thermostable phytase in feed and fuel industries

Phytase with wide ranging biochemical properties has long been utilized in a multitude of industries, even so, thermostability plays a crucial factor in choosing the right phytase in a few of the sectors. Mesophilic phytases are not considered to be a viable option in the feed industry owing to its limited stability in the required feed processing temperature. In the recent past, inclusion of thermostable phytase in fuel ethanol production from starch based raw material has been demonstrated with economic benefits. Therefore, considerable emphasis has been placed on using complementary approaches such as mining of extremophilic microbial wealth, encapsulation and using enzyme engineering for obtaining stable phytase variants. This article means to give an insight on role of thermostable phytases in feed and fuel industries and methods for its development, highlighting molecular determinants of thermostability.

Microbial phytase: Impact of advances in genetic engineering in revolutionizing its properties and applications

Phytases are enzymes that increase the availability of phosphorous in monogastric diet and reduces the anti-nutrition effect of phytate. This review highlights contributions of recombinant technology to phytase research during the last decade with specific emphasis on new generation phytases. Application of modern molecular tools and genetic engineering have aided the discovery of novel phytase genes, facilitated its commercial production and expanded its applications. In future, by adopting most recent gene improvement techniques, more efficient next generation phytases can be developed for specific applications.

Purification and characterization of a protease-resistant phytase of Aspergillus oryzae SBS50 whose properties make it exceptionally useful as a feed supplement

An extracellular phytase of Aspergillus oryzae SBS50 was purified to homogeneity using ammonium sulphate precipitation, ion-exchange and gel filtration chromatography. Purified phytase has a monomeric molecular mass of ∼80kDa exhibiting its optimal activity at pH 5.0 and 50°C with a T _1/2 of 300min at 50°C. Phytase of A. oryzae displayed broad substrate specificity with V_max and K_m values of 58.82μmol/ml/min and 1.14mM, respectively, for calcium phytate. Purity and homogeneity of the phytase was confirmed by high performance liquid chromatography and MALDI-TOF analysis revealed the identification of a peptide showing homology with acid phosphatase of Aspergillus oryzae RIB40. Among the inhibitors, 2,3-butanedione and sodium molybdate significantly inhibited the enzyme activity. Phytase of A. oryzae showed protease-resistance and was more stable during storage at 4°C and -20°C as compared to room temperature. Among all the feed samples, mustard oil cake was dephytinized more efficiently than other feed samples. These unique properties suggested that the phytase has the potential to be useful as an animal feed supplement.

Molecular advancements in the development of thermostable phytases

Since the discovery of phytic acid in 1903 and phytase in 1907, extensive research has been carried out in the field of phytases, the phytic acid degradatory enzymes. Apart from forming backbone enzyme in the multimillion dollar-based feed industry, phytases extend a multifaceted role in animal nutrition, industries, human physiology, and agriculture. The utilization of phytases in industries is not effectively achieved most often due to the loss of its activity at high temperatures. The growing demand of thermostable phytases with high residual activity could be addressed by the combinatorial use of efficient phytase sources, protein engineering techniques, heterologous expression hosts, or thermoprotective coatings. The progress in phytase research can contribute to its economized production with a simultaneous reduction of various environmental problems such as eutrophication, greenhouse gas emission, and global warming. In the current review, we address the recent advances in the field of various natural as well as recombinant thermotolerant phytases, their significance, and the factors contributing to their thermotolerance.

Recombinant HAP Phytase of the Thermophilic Mold Sporotrichum thermophile: Expression of the Codon-Optimized Phytase Gene in Pichia pastoris and Applications

The codon-optimized phytase gene of the thermophilic mold Sporotrichum thermophile (St-Phy) was expressed in Pichia pastoris. The recombinant P. pastoris harboring the phytase gene (rSt-Phy) yielded a high titer of extracellular phytase (480 ± 23 U/mL) on induction with methanol. The recombinant phytase production was ~40-fold higher than that of the native fungal strain. The purified recombinant phytase (rSt-Phy) has the molecular mass of 70 kDa on SDS-PAGE, with K m and V max (calcium phytate), k cat and k cat/K m values of 0.147 mM and 183 nmol/mg s, 1.3 × 10(3)/s and 8.84 × 10(6)/M s, respectively. Mg(2+) and Ba(2+) display a slight stimulatory effect, while other cations tested exert inhibitory action on phytase. The enzyme is inhibited by chaotropic agents (guanidinium hydrochloride, potassium iodide, and urea), Woodward's reagent K and 2,3-bunatedione, but resistant to both pepsin and trypsin. The rSt-Phy is useful in the dephytinization of broiler feeds efficiently in simulated gut conditions of chick leading to the liberation of soluble inorganic phosphate with concomitant mitigation in antinutrient effects of phytates. The addition of vanadate makes it a potential candidate for generating haloperoxidase, which has several applications.

Phytase-producing capacity of yeasts isolated from traditional African fermented food products and PHYPk gene expression of Pichia kudriavzevii strains

Phytate is known as a strong chelate of minerals causing their reduced uptake by the human intestine. Ninety-three yeast isolates from traditional African fermented food products, belonging to nine species (Pichia kudriavzevii, Saccharomyces cerevisiae, Clavispora lusitaniae, Kluyveromyces marxianus, Millerozyma farinosa, Candida glabrata, Wickerhamomyces anomalus, Hanseniaspora guilliermondii and Debaryomyces nepalensis) were screened for phytase production on solid and liquid media. 95% were able to grow in the presence of phytate as sole phosphate source, P. kudriavzevii being the best growing species. A phytase coding gene of P. kudriavzevii (PHYPk) was identified and its expression was studied during growth by RT-qPCR. The expression level of PHYPk was significantly higher in phytate-medium, compared to phosphate-medium. In phytate-medium expression was seen in the lag phase. Significant differences in gene expression were detected among the strains as well as between the media. A correlation was found between the PHYPk expression and phytase extracellular activity.

Replacement P212H altered the pH-temperature profile of phytase from Aspergillus niger NII 08121

Microbial phytase, a widely used animal feed enzyme, needs to be active and stable in the acidic milieu for better performance in the monogastric gut. Aspergillus niger phytases exhibit an activity dip in the pH range from 3.0 to 3.5. Replacement of amino acids, which changed the pKa of catalytic residues H82 and D362, resulted in alteration of the pH profile of a thermostable phytase from A. niger NII 08121. Substitution P212H in the protein loop at 14 Å distance to the active site amended the pH optimum from 2.5 to pH 3.2 nevertheless with a decrease in thermostability than the wild enzyme. This study described the utility of amino acid replacements based on pKa shifts of catalytic acid/base to modulate the pH profile of phytases.