Identification and Functional Characterization of Adenosine Deaminase in Mucor circinelloides: A Novel Potential Regulator of Nitrogen Utilization and Lipid Biosynthesis

Adenosine deaminase (ADA) is an enzyme distributed in a wide variety of organisms that cleaves adenosine into inosine. Since inosine plays an important role in nitrogen metabolism, ADA may have a critical function in the regulation of fatty acid synthesis. However, the role of ADA in oleaginous fungi has not been reported so far. Therefore, in this study, we identified one ada gene encoding ADA (with ID scaffold0027.9) in the high lipid-producing fungus, Mucor circinelloides WJ11, and investigated its role in cell growth, lipid production, and nitrogen metabolism by overexpressing and knockout of this gene. The results showed that knockout of the ada altered the efficiency of nitrogen consumption, which led to a 20% increment in the lipid content (25% of cell dry weight) of the engineered strain, while overexpression of the ada showed no significant differences compared with the control strain at the final growth stage; however, interestingly, it increased lipid accumulation at the early growth stage. Additionally, transcriptional analysis was conducted by RT-qPCR and our findings indicated that the deletion of ada activated the committed steps of lipid biosynthesis involved in acetyl-CoA carboxylase (acc1 gene), cytosolic malic acid enzyme (cme1 gene), and fatty acid synthases (fas1 gene), while it suppressed the expression of AMP-activated protein kinase (ampk α1 and ampk β genes), which plays a role in lipolysis, whereas the ada-overexpressed strain displayed reverse trends. Conclusively, this work unraveled a novel role of ADA in governing lipid biosynthesis and nitrogen metabolism in the oleaginous fungus, M. circinelloides.