ISOLATION OF ASPERGILLUS STRAINS FROM WASTEWATER-IMPACTED SOILS AND OPTIMIZATION OF ACID PHOSPHATASE PRODUCTION
Abstract
Wastewater-impacted agricultural soils may harbor fungi capable of producing extracellular phosphatases that participate in organic phosphorus turnover. This study screened indigenous fungal isolates recovered from agricultural soils irrigated with untreated wastewater in the Faisalabad region of Pakistan and evaluated shake-flask culture variables affecting acid phosphatase activity. Of 53 recovered isolates, 14 were described as preliminary phosphatase-positive and five candidates were prioritized by a plate-based halo index. The leading isolates were morphologically assigned to Aspergillus niger and Aspergillus fumigatus. Assays using p-nitrophenyl phosphate indicated initial acid phosphatase activities of 5.9 and 4.3 U/mL, respectively. Following the reported optimization procedures, these values increased to 19.0 ± 0.033 and 16.0 ± 0.033 U/mL, equivalent to approximately 3.22- and 3.72-fold increases. The experiments identified 250 µM substrate, an inoculum volume of 0.5 mL, pH 4, and 30 °C as favorable settings, with glucose supporting activity; however, the source contains conflicting descriptions of the optimal incubation period and nitrogen supplement. Crude preparations retained measurable activity across an acidic pH interval and a broad temperature range, with altered activity in the presence of several metal ions and inhibitors. These results support further evaluation of indigenous Aspergillus isolates as acid phosphatase sources, while molecular identification, assay normalization, reproducibility, and application-level validation remain necessary.
Keywords
- Acid phosphatase; Aspergillus niger; Aspergillus fumigatus; fungal isolation; p-nitrophenyl phosphate; shake-flask optimization; wastewater-irrigated soil.
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