Fungal phytases: from genes to applications
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BIOTECHNOLOGY AND INDUSTRIAL MICROBIOLOGY - REVIEW
Fungal phytases: from genes to applications Thamy Lívia Ribeiro Corrêa 1
&
Elza Fernandes de Araújo 1
Received: 20 August 2019 / Accepted: 30 April 2020 # Sociedade Brasileira de Microbiologia 2020
Abstract 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. Keywords Phytases . Filamentous fungi . Aspergillus Niger . phyA
Introduction: an overview on phytases Phytic acid, an inositol ring connected to six phosphate groups, is a natural constituent of plant-based foods. Nearly 60–90% of the inorganic phosphorus (Pi) in legumes, oilseeds, and cereals are stored as phytic acid [1], making Pi inaccessible for a range of metabolic processes essential for all living organisms such as energy metabolism/regulation and biosynthesis of nucleic acids/cell membranes [2, 3]. The protonation of the phosphate groups under acidic conditions generates the free form of phytic acid. At neutral pHs, the affinity of phytic acid for divalent and trivalent cations increases, especially for Mg+2, Ca+2, Cu2+, Zn2+, and Fe2+/ 3+ , giving rise to a low-solubility chelate known as phytate [4]. Through this chelating activity, phytic acid could form complexes with starch, proteins, and lipids [5]. Phytases (myo-inositol hexakisphosphate phosphohydrolases) are phosphatases which hydrolyze phytic acid preferentially into inositol and six Pi, but the release of mono-, di-, tri-, tetra-, or pentaphosphate intermediates is possible when a partial Responsible Editor: Eleni Gomes. * Thamy Lívia Ribeiro Corrêa [email protected] 1
Department of Microbiology/BIOAGRO, Federal University of Viçosa, Av. Peter Henry Rolfs s/n, Vicosa, MG 36570-000, Brazil
hydrolysis occurs. Phytases are classified according to the order of release of the phosphate groups from phytic acid in 3-phytases (E.C. 3.1.3.8), 4/6-phytases (E.C. 3.1.3.26), or 5-phytases (E.C. 3.1.3.72) [1, 6]. Phytases are ubiquitously produced by animals, plants, and microorganisms and usually exhibit optimal activity at pH and temperature of 4.5–6.0 and 45–60 °C, respectively, acidic pI, molecular weight around 40–70 kDa, and a monomeric state [7, 8]. Mullaney and Ullah [9] classified phytases into histidine acid (HAP
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