Regulation of the Aldehyde Dehydrogenase Gene (aldA) and Its Role in the Control of the Coinducer Level Necessary for Induction of the Ethanol Utilization Pathway in Aspergillus nidulans

Abstract

Expression of the structural genes for alcohol and aldehyde dehydrogenase, alcA and aldA, respectively, enables the fungus Aspergillus nidulans to grow on ethanol. The pathway-specific transcriptional activator AlcR mediates the induction of ethanol catabolism in the presence of a coinducing compound. Ethanol catabolism is further subject to negative control mediated by the general carbon catabolite repressor CreA. Here we show that, in contrast to alcA and alcR, the aldA gene is not directly subject to CreA repression. A single cisacting element mediates AlcR activation of aldA. Furthermore, we show that the induction of the alc gene system is linked to in situ aldehyde dehydrogenase activity. In aldA loss-of-function mutants, the alc genes are induced under normally noninducing conditions. This pseudo-constitutive expression correlates with the nature of the mutations, suggesting that this feature is caused by an intracellular accumulation of a coinducing compound. Conversely, constitutive overexpression of aldA results in suppression of induction in the presence of ethanol. This shows unambiguously that acetaldehyde is the sole physiological inducer of ethanol catabolism. We hypothesize that the intracellular acetaldehyde concentration is the critical factor governing the induction of the alc gene system.

Ethanolamine Catabolism in Pseudomonas aeruginosa PAO1 Is Regulated by the Enhancer-Binding Protein EatR (PA4021) and the Alternative Sigma Factor RpoN

“…In this microorganism, AlcR is a regulator of ethanol catabolism that responds directly to acetaldehyde and upregulates the transcription of genes encoding alcohol (alcA) and aldehyde (aldA) dehydrogenases (53,54). Similar to the situation described herein for P. aeruginosa PAO1, growth on compounds that are degraded into acetaldehyde induce expression of the alcA and aldA genes in Aspergillus nidulans (55,56).…”

“…The eutBC genes are in an operon with genes encoding an acetaldehyde dehydrogenase (PA4022) and an ethanolamine transporter (PA4023 or eat). The PA4022-eat-eutBC operon is preceded by a conserved Ϫ24/Ϫ12 promoter recognized by the alternative sigma factor 54 or RpoN (19)(20)(21). Unlike sigma factors of the 70 class, the RpoN RNA polymerase (RNAP) holoenzyme cannot spontaneously isomerize from a closed configuration to an open complex (19,22).…”

ATP-Citrate Lyase Is Required for Production of Cytosolic Acetyl Coenzyme A and Development in Aspergillus nidulans

“…In contrast, growth was normal on acetate or ethanol as sole carbon sources where cytoplasmic , it completely prevented repair by ethanol, consistent with strong glucose repression of ethanol catabolism (27). Growth on threonine was unaffected, and threonine repaired growth on proline, consistent with catabolism of threonine via acetaldehyde and acetate (16). The deletion strains were able to grow on butyrate and to a much lesser extent on valerate and oleate.…”

“…The utilization of ethanol as a sole carbon source is mediated by AlcA (alcohol dehydrogenase) and AldA (aldehyde dehydrogenase). The transcription of the genes for these enzymes is activated by the AlcR transcription factor, which responds to acetaldehyde as the inducer, and expression is repressed by carbon catabolite repression mediated by CreA, which represses alcR and alcA (16,27). There is a single cytoplasmic ACS encoded by facA, and loss-of-function mutations in this gene result in loss of growth on acetate or ethanol as sole carbon sources but have no effect on growth on glucose or amino acids, such as proline or glutamate (3,7,42).…”

Elucidação do destino metabólico de glicose no fungo filamentoso Trichoderma reesei por análise EST (Expressed Sequence Tags) e "microarrays" de cDNA.

“…Em Aspergillus sp. a repressão por glicose afeta três grupos de genes: a) sistemas enzimáticos envolvidos na degradação de polissacarídeos (celulose, pectina, xylose); b) enzimas da gliconeogênese e do ciclo do glioxalato; e c) enzimas relacionadas à produção de metabólitos secundários (por exemplo penicilina, em A nidulans) (Flipphi et al, 2001 O perfil de expressão gênica descrita em T. reesei é, possivelmente, adotado por outros microorganismos multicelulares para obter energia através da respiração, ao invés da fermentação. A informação obtida é importante na eventual tentativa de converter, por engenharia metabólica, este microorganismo, preferencialmente aeróbio, em um microorganismo anaeróbio; um procedimento pertinente para a produção de etanol a partir de biomassa celulósica.…”