E. coli versus fungal phytase: Focus on enzymatic properties
Phosphorus (P) is an essential nutrient for animals. It must be supplied in sufficient amounts in the feed to maintain health, body functions and performance. The amounts of total P present in most commercial diets are inherently high enough to meet the animals' requirements. However, the major portion (50-80 percent) of total P in plant feedstuffs is present as phytate (myo-inositol 1,2,3,4,5,6-hexakis dihydrogen phosphate), the primary storage form of P in plants (Pointillart et al., 1984).
Phytate contains 28.2 percent P, which is tightly bound in six phosphate groups. In this form, P is unavailable for absorption. Moreover, phytate binds positively charged minerals and trace elements (such as calcium, zinc, iron) and also protein, amino acids and starch, thereby reducing their bioavailability as well (Maga, 1982; Erdmann, 1979).
Non-ruminants such as poultry, pigs and fish lack gastrointestinal phytate-degrading enzymes, commonly referred to as phytases (Pointillart et al., 1984), hence limiting the availability of P and other nutrients for these species. Consequently, additional P from expensive inorganic sources (such as mono- or dicalciumphosphate) must be included in diets for non-ruminants to meet their P requirements.
However, there is growing awareness on excessive P output from livestock production systems, which increases the risk of severe environmental pollution.
A powerful measure to counteract the poor P utilisation in non-ruminants is to include exogenous phytase into the feed. Phytase breaks down the phytic acid molecule within the digestive tract and provides inorganic P and other bound nutrients for absorption.
While various phytase preparations are commercially available to the feed industry, there are distinct differences in efficacy between these enzymes. The first phytase preparations were industrially produced from fungi. However, deficiencies in enzymatic properties, including efficiency in phytate hydrolysis rate, thermal stability and pH optimum have driven strong efforts to discover other sources of phytase with improved efficacy.
Development of bacterial phytase originating from E. coli has recently attracted considerable attention of scientists and nutritionists worldwide. Enzyme engineering using state-of-the-art molecular methods and modern fermentation techniques has now resulted in a big step forward to improve phytase efficacy.
Augspurger et al. (2003) demonstrated that E. coli phytase was more efficient in hydrolyzing phytate than fungal phytase.
Generally, the effects of phytases on digestibility and performance are determined by the concurrence of intrinsic enzyme activity, action time and inactivation (such as by proteases in the small intestine). Hence, an efficient commercial phytase enzyme should reveal high intrinsic activity over a broad range of pH and temperature, and the residence time in the stomach should be long enough to hydrolyze a large portion of dietary phytate.
On the other hand, feed enzymes are usually susceptible to heat, harsh pH conditions and proteolytic enzymes, altogether resulting in gradual deactivation of the enzyme. Furthermore, concentrations of P, calcium trace elements and vitamin D affect the in vivo efficacy of phytase.
In conclusion, the in vivo efficacy of phytase enzymes is largely determined by their intrinsic properties, such as activity at different pH conditions, resistance against proteolytic degradation and thermal stability. E. coli phytase has higher efficacy compared with fungal phytase, contributing substantially to optimal P management and efficient utilisation of P sources.
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Article made possible through the contribution of Biomin.