Repression of the acid ZrfA/ZrfB zinc-uptake system of Aspergillus fumigatus mediated by PacC under neutral, zinc-limiting conditions

The ZrfA and ZrfB transporters are components of a zinc-uptake system of Aspergillus fumigatus that mainly operates under acidic, zinc-limiting conditions. Expression of the genes zrfA and zrfB is up-regulated by the transcriptional activator ZafA in both acidic and neutral, zinc-limiting media. The transcription of zafA is not influenced by PacC, which is the transcriptional regulator involved in regulating pH homeostasis in Aspergillus. However, at neutral pH the expression of both zrfA and zrfB is significantly reduced. In this work, the repression of zrfA and zrfB in neutral and alkaline, zinc-limiting media was found to be mediated by the transcriptional regulator PacC (AU)

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Carbon catabolite repression of retamycin production by Streptomyces olindensis ICB20

Retamycin is an anthracyclinic antitumoral complex produced by Streptomyces olindensis ICB20. In this work the influence of different glucose concentrations in the feed medium on the production of retamycin was studied. Chemostat cultures employing glucose concentration varying between 10 g/L and 25 g/L showed that use of high glucose concentration resulted in catabolite repression of the biosynthesis of the antitumoral. The highest specific retamycin production rate, qRTM = 7.8 mg/g.h, was obtained when glucose concentration was 10 g/L. The lowest value of qRTM, 2.5 mg/g.h, was observed when glucose concentration was 20 and 25 g/L. The residual glucose concentration varied from 0 to 13 g/L, as the glucose concentration in the feed was increased from 10 to 25 g/L.

A retamicina é um complexo antitumoral antraciclínico produzido por Streptomyces olindensis ICB20. Neste trabalho estudou-se a influência de diferentes concentrações de glicose no meio de alimentação sobre a produção de retamicina. Os resultados de cultivos contínuos mostraram que o uso de elevadas concentrações de glicose resultou em repressão catabólica da biossíntese do antitumoral. A maior velocidade específica de produção de retamicina, qRTM = 7,8 mg/g.h, foi obtida quando a concentração de glicose foi de 10 g/L. O menor valor de qRTM, 2,5 mg/g.h, foi observado quando a concentração de glicose foi de 20 e 25 g/L. A concentração de glicose residual aumentou de 0 a 13 g/L conforme a concentração de glicose na alimentação foi incrementada de 10 a 25 g/L.

The NADP+-dependent glutamate dehydrogenase of the yeast Kluyveromyces marxianus responds to nitrogen repression similarly to Saccharomyces cerevisiae

Glutamato desidrogenase dependente de NADP+ (NADP+-Gdh) constitui o primeiro passo enzimático no mecanismo de assimilacão de nitrogênio em Saccharomyces cerevisiae e o conhecimento de sua regulacão é chave na iniciativa de vários propósitos biotecnológicos, tais como a producão de proteína microbiana. A regulacão da atividade NADP+-Gdh em células de Kluyveromyces marxianus foi avaliada a partir de diferentes condicões de suprimento de amonia em cultivo em batelada. Os resultados mostraram que a atividade NADP+-Gdh de K. marxianus foi induzida em uma estreita faixa de concentracão de amonia no meio, sendo reprimida tanto por altas concentracões deste composto quanto pelo produto glutamato. Esta atividade não está associada ao crescimento celular e deve funcionar principalmente no rastreamento de pequenas quantidades de amonia após a parada do crescimento celular. Isto demonstra que NADP+-Gdh não deve ser a principal enzima de assimilacão de amonia em K. marxianus, como tem sido postulado para K. lactis, contudo deve estar submetida ao mesmo mecanismo regulatório encontrado em S. cerevisiae.

The transcription factor Snf1p is involved in a Tup1p-independent manner in the glucose regulation of the major methanol metabolism genes of Hansenula polymorpha

Hansenula polymorpha is a methylotrophic yeast widely employed in biotechnology as a ''protein factory''. Most promoters used for heterologous protein expression, like MOX (methanol oxidase) and DAS (di-hydroxy acetone synthase), are involved in the peroxisomal methanol metabolism (C1 metabolism) and are under strong glucose repression. Interestingly, the MOX promoter is subjected to glucose regulation also in Saccharomyces cerevisiae, a non-methylotrophic yeast in which this phenomenon is well studied. In this species, the transcription factor Tup1p plays an essential role in glucose repression of several genes. This effect is counteracted by the activator Snf1p when glucose is exhausted from medium. Therefore, to test whether this regulatory circuit has been conserved in H. polymorpha, HpTUP1 and HpSNF1 were partially cloned and disrupted. Deletion of HpTUP1 did not affect glucose repression of the major C1 metabolism genes (MOX, DAS). Thus, though conserved, HpTUP1 does not seem to take part in a general glucose repression in H. polymorpha. In contrast, the deletion of HpSNF1 led to significant decreases in the activation of these genes in the absence of glucose. Therefore, the effect of HpSNF1 in transcriptional activation may be through an HpTUP1- independent circuit.

Production of glucoamylase by fed-batch culture of Aspergillus awamori NRRL3112

A produçäo de amiloglicosidase por Aspergillus awamori NRRL3112 em processo descontínuo alimentado é 92 por cento superior em relaçäo ao processo descontínuo em cultivos com 20 g/l de concentraçäo total de fonte de carbono oriunda de farinha de mandioca. Uma análise da velocidade específica de produçäo mostra ser este resultado decorrente da reduçäo do efeito repressivo causado pela glicose, já que o efeito indutivo, relacionado à concentraçäo de polissacarídeo, também foi reduzido

Effect of carbon source and extracellular pH on the acidification of the culture medium and phosphatase excretion in Neurospora crassa

Exogenous Ca2+ at concentrations up to 3.5 mM increases the sucrose-induced acidification of the culture medium when the mold Neurospora crassa is grown on low-phosphate (Pi) medium at pH 7.8. Induction depends on the pH of the culture medium adjusted for conidial inoculation and on the absence of carbon sources generating cytoplasmic acetyl CoA. Furthermore, the excretion of Pi-repressible acid and alkaline phosphatases was not stimulated by increasing exogenous Ca2+ levels. We also provide evidence that the extracellular pH monitoring by Neurospora crassa may be a determinant in the selective excretion of Pi-repressible acid and alkaline phosphatases.