الملخص الإنجليزي
Phytases are enzymes that hydrolyse phytic acid into myo-inositol monophosphate and
soluble inorganic phosphates. In monogastric animals, phytase activity enhances the
absorbance of phosphorous and minerals and decreases the antinutrient activity of feed
phytate. The general objective of this study was to screen Omani saline soils for novel
fungal phytases suitable for application as feed additives for poultry diets. The study
hypothesized that soil salinity would exert selection pressure on fungal communities,
allowing for the isolation of less common fungal strains, and increasing the probability
of finding novel fungal phytases among the isolates. The initial phase showed saline soils
have a lower abundance of fungal colonies, but a higher abundance of morphologically
different strains. Sixteen fungi were isolated from five soil samples collected from
different sites in Muscat and Al-Batinah South Governorates. Ten Ca-phytate degrading
fungal isolates were selected for forming clear zones on Phytase Screening Media (PSM).
To further confirm their phytate degrading activity, the ten isolates were subjected to
quantitative assays and only seven isolates showed the release of extracellular
phosphorous between 318 and 1197 mg L
-1 when grown for six days at 37 C in broth
media supplemented with 0.5% Na-phytate. The fungal isolates able to release
extracellular P from phytate were identified by ITS sequencing as Penicillium vinaceum,
Penicillium citrinum, Aspergillus terreus and Citeromyces sp. The Citeromyces sp. strain
ITS sequence showed only 77% coverage with deposited sequences in NCBI.
Additionally, no literature has previously described biochemical characterization
phytases in Citeromyces sp. The pH-dependency of the phytase activity was assayed
between (pH = 2.0 to 9.0), and the enzyme's thermostability and thermodynamic
parameters were evaluated at temperatures between (30 to 80 C) with activity assays of
increasing duration (Time = 30 to 60 minutes). The optimum Na-phytase concentration
for the Citeromyces sp. phytase was 2.3 mM at pH = 4. Over 70% of the activity was
retained at acidic pH between (3.0 to 6.5) at high temperatures between (60 to 80 C),
while the maximum phytase assay was detected within 30 to 40 min. This study
demonstrates that our Citeromyces sp. isolate produces a novel thermotolerant acid
phytase. In addition, this enzyme showed the ability to remain active for 80 min
incubation under acid conditions of pH = 4.0 at 40 C and withstand temperatures up to
80 C. This novel phytase showed thermotolerant properties desired by industry and
therefore has a high potential for further biotechnological application as a feed enzyme
additive. Further in vitro and in vivo assays are recommended to test industrial
applications for this enzyme.
