Screening of Aspergillus and Candida Species with Utmost Potential to Synthesize Citric Acid

Background: Citric acid production through fermentation is economical but meeting its increasing global demand has been challenging in recent times. Aim: This study aimed to screen Aspergillus and Candida sp. isolated from different sources with potentials of producing citric acid. Methodology: Aspergillus and Candida spp. were isolated from compost soil and fruits (cucumber and banana) and their morphological characteristics were described using standard microbiological methods. The isolates were quantitatively screened for citric acid production based on appearance of yellow zone of clearance for 3 days. All the isolates which had acid unitage (AU) values> 5.0 were selected for further characterization using molecular methods. Results: Candida tropicalis, Aspergillus sp. A. niger and Penicillium sp. were isolated from the soil and fruit samples. The isolates screened for citric acid production displayed varying diameters of yellow zones around their colonies is indicative of varying capability of the microbial strains. A. niger from compost soil which had highest AU value of 8.5 at Day 3 demonstrated greatest potential to yield citric acid. Molecular characterization revealed high citric acid producing strains as Aspergillus niger (EU440768.1) and Aspergillus welwitschiae (MG669181.1). Conclusion: Although Aspergillus niger is widely utilized for industrial production of citric acid, this study has demonstrated that A. welwitschiae is a specie of Aspergillus capable of synthesizing citric acid reasonably.