The Regulatory Effect of Nitrogen Metabolism Regulator AreB on Lipid Accumulation in Oleaginous Fungus Mucor circinelloides

Nitrogen metabolite repression (NMR) represents a conserved regulatory system governing nitrogen utilization in filamentous fungi. The GATA-type transcription factor AreA serves as an activator under nitrogen-limited conditions, while AreB functions as a negative antagonist that competes with AreA for GATA cis-elements within target promoters. Previous studies in Mucor circinelloides have demonstrated that AreA can regulate key nitrogen metabolic genes and orchestrates carbon–nitrogen balance to promote lipid accumulation. Nevertheless, the function of AreB remains uncharacterized in this oleaginous fungus. In this study, the areB homologous gene was identified from the genome of M. circinelloides through bioinformatic prediction. Subsequently, we constructed the areB-knockout and areB-overexpression strains to elucidate the regulatory role of AreB in cell growth, carbon and nitrogen utilization, and lipid accumulation. Fermentation phenotypic assays showed that deletion of areB significantly improved cell growth, yielding a 15.81% increase in biomass compared with the wild-type, while the lipid content showed a moderate increase of 9.7%. In contrast, overexpression of areB exerted negligible effects on biomass (17.84 g/L versus 17.08 g/L in the control) and slightly reduced the lipid content (from 25.85% to 25.17%). When cultivated under diverse nitrogen sources, the ΔareB strain displayed markedly enhanced lipid content with glutamate as the sole nitrogen source. Subsequent transcriptomic analysis revealed that deletion of areB redirects carbon flux towards fatty acid biosynthesis. This work extends the nitrogen regulatory network in M. circinelloides and provides potential targets for metabolic engineering aimed at improving lipid production.