Regulation of energy metabolism in filamentous fungi: Uncoupling of catabolism and anabolism at energy excess conditions illustrated by Penicillium simplicissimum

Molds excrete high amounts of acids under specific culture conditions. This property is used in biotechnological processes, for instance to produce citric acid on an industrial scale with Aspergillus niger or to win metals from industrial secondary raw materials and low grade ores with Penicillium simplicissimum ("biohydrometallurgical leaching processes"). This acid excretion plays also a role in ecological relationships, because acids excreted in soil can solubilize trace elements and make them available as nutrients. On the level of the whole metabolism the regulation of this acid excretion is only poorly understood in molds - in contrast to yeasts. A first systematic investigation of several environmetal conditions, which are important for acid excretion, was made with the fungus Penicillium simplicissimum in a chemostat during an Austrian Science Fund project, which was finished in 2002. Penicillium simplicissimum excreted organic acids if growth was limited and the carbon source was in excess. The amount of excreted acids depended on the kind of the growth limiting nutrient. A deficiency of phosphorus resulted in the highest acid excretion. Additional stress factors - for instance a high osmolarity - increased the acid excretion. The results of the mentioned Austrian Science Fund project indicated that the central "energy currencies" of the cell - the molecules ATP and NADH - might play an important role for the excretion of acids. In this project, therefore, we want to study the influence of ATP, NADH, and a few other compounds important for energy metabolism, on acid excretion. Beyond this question the results of this project will help to better understand the regulation of the so-called "primary metabolism" in molds, i. e. that part of metabolism which produces energy and small cell components. A deeper understanding of the primary metabolism can, for instance, also be relevant for the production of medically important proteins, for which molds are increasingly used.

Molds excrete high amounts of acids under specific culture conditions. This property is used in biotechnological processes, for instance to produce citric acid on an industrial scale with Aspergillus niger or to win metals from industrial secondary raw materials and low grade ores with Penicillium simplicissimum ("biohydrometallurgical leaching processes"). This acid excretion plays also a role in ecological relationships, because acids excreted in soil can solubilize trace elements and make them available as nutrients. On the level of the whole metabolism the regulation of this acid excretion is only poorly understood in molds - in contrast to yeasts. A first systematic investigation of several environmetal conditions, which are important for acid excretion, was made with the fungus Penicillium simplicissimum in a chemostat during an Austrian Science Fund project, which was finished in 2002. Penicillium simplicissimum excreted organic acids if growth was limited and the carbon source was in excess. The amount of excreted acids depended on the kind of the growth limiting nutrient. A deficiency of phosphorus resulted in the highest acid excretion. Additional stress factors - for instance a high osmolarity - increased the acid excretion. The results of the mentioned Austrian Science Fund project indicated that the central "energy currencies" of the cell - the molecules ATP and NADH - might play an important role for the excretion of acids. In this project, therefore, we want to study the influence of ATP, NADH, and a few other compounds important for energy metabolism, on acid excretion. Beyond this question the results of this project will help to better understand the regulation of the so-called "primary metabolism" in molds, i. e. that part of metabolism which produces energy and small cell components. A deeper understanding of the primary metabolism can, for instance, also be relevant for the production of medically important proteins, for which molds are increasingly used.