The Phenylacetic Acid Uptake System of Aspergillus nidulans is under a creA-Independent Model of Catabolic Repression which Seems to be Mediated by Acetyl-CoA

Abstract

The filamentous fungus Aspergillus nidulans is able to grow on phenylacetic acid (PhAc) as the sole carbon source and has a highly specific phenylacetic acid transport system mediating the uptake of this aromatic compound. This transport system is also able to transport some phenoxyacetic acid (PhOAc), although less efficiently. Maximal uptake rates were observed at 37°C in 50 mM phosphate buffer (pH 7.0). Under these conditions, uptake was linear for at least 1 minute, with Km values for PhAc and PhOAc of 74 and 425 μM, respectively. The PhAc transport system is strongly induced by PhAc and, to a lesser extent by PhOAc and other phenyl derivatives. The utilization of glucose (and other sugars), glycerol or acetate results in a substantially reduced uptake. This negative effect caused by certain carbon sources is independent of the creA gene, the regulatory gene mediating carbon catabolite repression. Negative regulation by acetate is prevented by a loss-of-function mutation in the gene encoding acetyl-CoA synthetase, strongly suggesting that this regulation is mediated by the intracellular pool of acetyl-CoA.