Background and Objectives: Microorganisms that are capable of accumulating lipid up to 20% of their biomass are called oleaginous microorganisms. In this study, optimization in lipid and linolenic acid production was investigated in Aspergillus niger as an oleaginous filamentous fungi.

Methods: In this study, at first different strains of filamentous fungi were isolated, and after staining of the isolates with Sudan Black, their oil was extracted using chloroform/methanol. Then, the isolates with oil/dry biomass ratio of more than 20% were considered as oleaginous filamentous fungi. After microscopic examination, the identified isolate was optimized in terms of oil production. Finally, the amount of linolenic acid was evaluated using gas chromatography.

Results: At first, 20 filamentous fungi isolates were isolated. According to the results of Sudan Black staining, lipid inclusions were observed in all the fungal isolates. The amount of oil produced in all isolates, showed that the percentage of oil production in isolates 4, 5, and 16, was more than 20%. In microscopic examination, the isolate 5 was Aspergillus niger. The best pH, temperature, time, and carbon source for oil production by Aspergillus niger was 4.5, 30°C, 96 hours, and fructose, respectively. The amount of linolenic acid in Aspergillus niger was reported 22.4% using gas chromatography.  

Conclusion: The results of this study revealed that Aspergillus niger is an appropriate filamentous fungi for linolenic acid production.