Assessment of the amylase activities of aquatic fungi isolated from warm springs of Yankari Game Reserve, Bauchi State, Nigeria

Abstract

Aquatic fungi are important components of freshwater ecosystems and are recognized for their ability to produce industrially relevant enzymes and degrade environmental pollutants. However, information on the amylolytic potential of aquatic fungi inhabiting the warm springs of Yankari Game Reserve, Bauchi State, Nigeria, remains limited. This study assessed the amylase activity of aquatic fungi isolated from these warm springs and evaluated their potential for hydrocarbon biodegradation. Water samples were collected from four warm springs (Dimil, Gwana, Wikki, and Mawulgo), and fungal isolates were obtained using the baiting technique, followed by purification and identification based on morphological characteristics. Crude amylase was produced through submerged fermentation, and enzyme activity was determined using the dinitrosalicylic acid (DNS) method. The fungal isolates were further evaluated for viable counts, biomass accumulation, and biodegradation of waste engine oil (WEO), diesel, and petrol using standard microbiological and gravimetric techniques. Data were analysed using one-way analysis of variance (ANOVA), with statistical significance set at P < 0.05. Five aquatic fungal genera were identified: Achlya, Aphanomyces, Saprolegnia, Leptolegnia, and Brevilegnia. Saprolegnia spp. exhibited the highest occurrence (36.36%), whereas Achlya spp. recorded the highest amylase activity (0.93 µmol/min) on day 3, followed by Aphanomyces spp. (0.73 µmol/min), with significant differences observed among the isolates (P < 0.05). During WEO utilization, all fungal isolates showed progressive increases in viable counts and biomass, indicating active growth on hydrocarbons. Aphanomyces spp. demonstrated the highest biodegradation efficiency, achieving 50.09%, 48.23%, and 42.24% degradation of WEO, diesel, and petrol, respectively. These findings demonstrate that the warm springs of Yankari Game Reserve harbour aquatic fungi with significant amylolytic and hydrocarbon-degrading capabilities. The indigenous fungal isolates, particularly Achlya spp. and Aphanomyces spp., possess considerable potential for industrial enzyme production and the bioremediation of hydrocarbon-contaminated environments.

Keywords: Aquatic fungi, amylase activity, Achlya, Aphanomyces, hydrocarbon biodegradation, bioremediation.