Isolation, Identification and Screening of Fungal Isolates for Humic Acid Production

Abstract

Sustainable biotechnological processes have encouraged the search for efficient microorganisms capable of converting agricultural and organic wastes into valuable bio-products such as humic acids. Soil samples were obtained from dump sites of an oil palm processing farm in Obokun, Osun State. The soil sample was subjected to serial dilution and plated on Potato Dextrose agar plating technique to isolate distinct fungal colonies. Fungal isolates were purified, and identified by morphological and cultural characteristics and screened for growth performance based on colony diameter and fungal biomass, while humic acid production was assessed using a submerged fermentation process. Molecular analysis confirmed two isolates identified as Aspergillus flavus (PX097504) and Fusarium sp. Comparative growth analysis revealed that A. flavus demonstrated superior performance in both colony diameter (30.50 ± 0.09 mm) and fungal biomass (2.49 ± 0.02 g) when compared to Fusarium sp. (28.64 ± 0.04 mm and 1.98 ± 0.02 g, respectively). During fermentation, Fusarium sp. initially showed slightly higher humic acid production at the early stages (0.90 mg/L on day 1 and 1.10 mg/L on day 2); however, A. flavus outperformed it in subsequent days, achieving a maximum humic acid concentration of 2.20 mg/L by day 5. The findings demonstrate the potential of indigenous fungal isolates for bioconversion of organic wastes into humic substances, offering an environmentally-friendly approach to waste management and soil enrichment.