Molecular phylogenetic characterization of L-asparaginase-producing endophytic fungi inhabiting Prunus africana and Periploca linearifolia: Effect of incubation time and pH on enzyme production

Abstract

The therapeutic use of L-asparaginase derived from bacterial sources has been constrained by various challenges, including toxicity and repression. This has prompted the exploration of alternative sources, particularly eukaryotic microorganisms like fungi, to enhance the safety and effectiveness of the L-asparaginase enzyme. This study aims to investigate the fungal endophytes inhabiting Periploca linearifolia and Prunus africana as a potential source of novel L-asparaginase. Additionally, the study seeks to examine the impact of incubation time and pH on L-asparaginase production. Standard surface sterilization techniques were used for isolation of endophytic fungi. Based on the research findings, 24 % of the fungal endophytes demonstrated a positive reaction for L-ASNase activity and were identified as Colletotrichum sydowii, Fusarium sporotrichioides, Fusarium solani, Cercospora canescens, Penicillium crustosum, Penicillium pancosmium, Phoma sp, Penicillium ubiquetum, septoria sp and Penicillium commune. A significant variation in the production of L-asparaginase based on the time of incubation and pH was observed. Most endophytic fungal isolates exhibit optimal enzyme activity on the 6th day of incubation. However, both Septoria sp and Colletotrichum sydowii recorded the highest L-asparaginase activity on the 9th day of incubation. Fusarium solani demonstrated peak activity of 12.4 ± 1.12 UI/mL on the 12th day of incubation. The optimal pH for L-asparaginase production by fungal endophytes was found to be between 5 and 6. The fungal endophytes isolated from medicinal plants have the potential to serve as sources of novel L-asparaginase. Furthermore, it is evident that fungal endophytes display considerable variation in L-asparaginase production, influenced by the duration of incubation and pH conditions.