Production of phytase in a low phosphate medium by a novel yeast Candida krusei

Phytases are a special class of phosphatases that catalyze the sequential hydrolysis of phytate to less-phosphorylated myo-inositol derivatives and inorganic phosphate. Bacillus phytases, which exhibit their desirable activity profile under neutral pH, higher thermal stability, and strict substrate specificity for the calcium-phytate complex, have considerable potential in commercial and environmental applications. This review describes recent findings concerning the production, biochemical properties, molecular characteristics, and expression of Bacillus phytases. Several potential applications of the Bacillus phytases in animal nutrition, human health, and synthesis of lower myo-inositol phosphates are also summarized.

Bacillus phytases: present scenario and future perspectives.

Phytate (myo-inositol hexakisphosphate salts) can constitute a large fraction of the organic P in soils. As a more recalcitrant form of soil organic P, up to 51 million metric tons of phytate accumulate in soils annually, corresponding to ∼65% of the P fertilizer application. However, the availability of phytate is limited due to its strong binding to soils via its highly-phosphorylated inositol structure, with sorption capacity being ∼4 times that of orthophosphate in soils. Phosphorus (P) is one of the most limiting macronutrients for agricultural productivity. Given that phosphate rock is a finite resource, coupled with the increasing difficulty in its extraction and geopolitical fragility in supply, it is anticipated that both economic and environmental costs of P fertilizer will greatly increase. Therefore, optimizing the use of soil phytate-P can potentially enhance the economic and environmental sustainability of agriculture production. To increase phytate-P availability in the rhizosphere, plants and microbes have developed strategies to improve phytate solubility and mineralization by secreting mobilizing agents including organic acids and hydrolyzing enzymes including various phytases. Though we have some understanding of phytate availability and phytase activity in soils, the limiting steps for phytate-P acquisition by plants proposed two decades ago remain elusive. Besides, the relative contribution of plant- and microbe-derived phytases, including those from mycorrhizas, in improving phytate-P utilization is poorly understood. Hence, it is important to understand the processes that influence phytate-P acquisition by plants, thereby developing effective molecular biotechnologies to enhance the dynamics of phytate in soil. However, from a practical view, phytate-P acquisition by plants competes with soil P fixation, so the ability of plants to access stable phytate must be evaluated from both a plant and soil perspective. Here, we summarize information on phytate availability in soils and phytate-P acquisition by plants. In addition, agronomic approaches and biotechnological strategies to improve soil phytate-P utilization by plants are discussed, and questions that need further investigation are raised. The information helps to better improve phytate-P utilization by plants, thereby reducing P resource inputs and pollution risks to the wider environment.

https://pubs.acs.org/doi/pdf/10.1021/acs.est.2c00099

Enhancing Phytate Availability in Soils and Phytate-P Acquisition by Plants: A Review

Plants respond to their external environment to optimize their nutrition and production potential to minimize the food security issues and support sustainable agriculture system. Phosphorus (P) is an important nutrient for plants and is involved in plant metabolic processes. It is mostly available as orthophosphate and has a tendency to form complexes with cations. It has low mobility in soil, thus becoming unavailable for plant uptake that causes a reduction in plant growth and yield. Besides free P, phytate is the major form of organic P in soil and plant tissues. Phytases obtained from different sources, that is, plants, animals, and microorganisms, catalyze the hydrolysis of phytate and release available forms of inorganic P. The knowledge of mechanisms involved in catalytic activity of phytase obtained from microorganisms in soil is limited. This review summarizes the role of microbial phytase in releasing organic P by hydrolysis of phytate and factors affecting its activity in the soil.

Microbial phytase activity and their role in organic P mineralization

Phytate-degrading enzymes, also known as phytases, have a wide distribution in plants, microorganisms and some animal tissues (Konietzny and Greiner, 2002; see Hill and Richardson, Chapter 5, and Mullaney and Ullah, Chapter 7, this volume). They belong to a special class of phosphomonoesterases termed myo-inositol hexakisphosphate phosphohydolases, which are capable of initiating the stepwise release of phosphate residues from phytate (salts of myo-inositol hexakisphosphate), the major storage form of phosphate in plant seeds and pollen. The ability of such enzymes to hydrolyse phytate is usually known only from in vitro assays, and information on their in vivo function is rather limited. As enzymes are classified in general by their in vivo function, the term ‘phytate-degrading enzyme’ is preferred here to the term ‘phytase’, and is used throughout the chapter. The classification of enzymes as phytases based solely on in vitro assays becomes problematic when considering enzymes such as glucose-1-phosphatase in Escherichia coli and Enterobacter cloacae. This enzyme can hydrolyse phytate, albeit slowly, in vitro even though this is clearly not its in vivo function. Unless otherwise stated, designation of an enzyme as ‘phytatedegrading’ is based on in vitro assay using soluble sodium phytate. Phytate-degrading Enzymes and Their Classification

Phytate-degrading enzymes: regulation of synthesis in microorganisms and plants.

A bacterial strain producing high level of an extracellular phytase was isolated from cooked rice and identified as a strain of Bacillus sp. and designated as Bacillus sp. KHU-10. Optimum culture conditions were investigated for the maximum productivity of phytase by Bacillus sp. KHU-10. 1.0% Maltose and 1.0% peptone with 0.5% beef extract were the best carbon source and nitrogen source, respectively. The addition of CaCl 2 stimulated the enzyme productivity with concentration between 0.01% and 0.2%, in the medium. Although sodium phosphate increased the cell mass, the enzyme activity decreased. Calcium phytate and wheat bran containing phytate did not enhance the enzyme production. Under the optimum medium, the production of the phytase reached the highest level of 0.2 unit/ml after 4 days of incubation.

Isolation of a phytase-producing Bacillus sp. KHU-10 and its phytase production

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Isolation of a phytase-producing Bacillus sp. KHU-10 and its phytase production