Characterization and Optimization of L-Malic Acid Production by Some Clinical Isolates of Aureobasidium pullulans

Background: Poly-L-malic acid (PLMA) comprises aliphatic polyester polymers with broad applications in pharmaceutical industries. The fungal microorganisms are among the best natural sources recruited to supply L-malic acid (MA) as a precursor of PLMA. In this study, we investigated MA production ability of ۷ clinical isolated of the fungus Aureobasidium pullulans. Materials and Methods: Seven clinical isolates of A. pullulans acquired from Westerdijk Fungal Biodiversity Institute were studied, and the isolate with the highest total MA production was selected for the optimization process. We tried to optimize the output by applying different concentrations of CaCO۳ in fungus medium (۱.۵%, ۳%, and ۶%) and various incubation temperatures (۲۷°C, ۳۲°C, and ۳۷°C) during ۳, ۷, and ۱۴ days. Results: Intra-strains variation was significantly strong (P<۰.۰۰۰۱), and the highest production of MA was carried out by the isolate A. pullulans var. melanigenum dH ۲۱۹۳۱, UTHSC ۰۶-۴۵۶. The amount of MA produced by this strain was significantly higher in medium with ۳% CaCO۳ compared with other concentrations of CaCO۳ and after ۷ days incubation than the other fermentation times (P<۰.۰۵). Although MA production was higher at ۲۷°C, the differences between the investigated various temperatures were not significant (P>۰.۰۵). Conclusion: Overall, we obtained the highest MA production in Sabouraud dextrose agar (SDA)medium with ۳% CaCO۳ at ۲۷°C after ۷ days of incubation. Our study indicated that the fermentation period and CaCO۳ concentration significantly alter MA production in A. pullulans var. melanigenum.

Keywords:

Poly-L-malic acid , L-malic acid , Aureobasidium pullulans , Fungi , Fungal Natural products