Efflux of organic acids in Penicillium simplicissimum is an energy-spilling process, adjusting the catabolic carbon flow to the nutrient supply and the activity of catabolic pathways

Abstract

Continuous cultivation was used to study the effect of glucose, ammonium, nitrate or phosphate limitation on the excretion of tricarboxylic acid (TCA) cycle intermediates by Penicillium simplicissimum. Additionally, the effect of benzoic acid, salicylhydroxamic acid (SHAM) and 2,4-dinitrophenol on TCA cycle intermediates was studied. The physiological state of the fungus was characterized by its glucose and O 2 consumption, its CO 2 production, its intraand extracellular concentrations of TCA cycle intermediates, as well as by its biomass yield, its maintenance coefficient and its respiratory quotient. The excretion of TCA cycle intermediates was observed during ammonium-, nitrateand phosphate-limited growth. The highest productivity was found with phosphate-limited growth. The respiratory quotient was 13 under ammonium limitation and 07 under phosphate limitation. Citrate was always the main excreted intermediate. This justifies calling this excretion an energy-spilling process, because citrate excretion avoids the synthesis of too much NADH. The addition of benzoic acid further increased the excretion of TCA cycle intermediates by ammonium-limited hyphae. A SHAM-sensitive respiration was constitutively present during ammonium-limited growth of the fungus. The sum of the excreted organic acids was negatively correlated with the biomass yield (Y GlcX ).

Organic Acid Excretion in Penicillium ochrochloron Increases with Ambient pH

“…Chemostat experiments were performed in a Biostat M bioreactor (Sartorius/Braun, working volume of 1.7 L, bioreactor equipped with an overflow device) under ammonium limitation (medium composition see Gallmetzer and Burgstaller, 2002; cultivation conditions as described in Gallmetzer and Burgstaller, 2001). For pH-shift experiments the culture pH was raised stepwise (Gallmetzer, 2000): starting with an initial pH of 2, the culture pH was adjusted with sodium hydroxide to the desired next pH level (pH 4, 6, and 7).…”

Characterisation of AnBEST1, a functional anion channel in the plasma membrane of the filamentous fungus, Aspergillus nidulans

“…It is highly likely that anion channels mediate the passive efflux of anions from fungi as a result of them possessing a highly negative potential across the plasma membrane maintained by a H + pumping ATPase. Efflux of organic anions is a characteristic feature of fungi and, analogous to that described in plants (Roberts, 2006), secretion of organic anions by fungi is thought to play important roles in nutrient acquisition, chelation and detoxification of metals (Gadd, 2007) and in providing a shunt conductance in the adaptation and tolerance to acid stress (Sanders et al, 1981;Gallmetzer and Burgstaller, 2002). Thus it is likely that plasma membrane anion channels mediate organic anion efflux from fungi and the identification of the genes encoding plasma anion channels in fungi could be important in providing further insights into the role of organic anion efflux in fungal biology.…”

Characteristics of glucose uptake by glucose- and NH4-limited grown Penicillium ochrochloron at low, medium and high glucose concentration

“…Metal leaching by P. ochrochloron is achieved via excreted organic acids, mainly citrate (Schinner and Burgstaller, 1989). Citrate excretion is a special case of overflow metabolism, which is the excretion of incompletely oxidized metabolites at limited growth and carbon source excess (Holms, 1996;Teixeira De Mattos and Neijssel, 1997;Gallmetzer and Burgstaller, 2002). The extent of overflow metabolism depends partly on the glucose uptake rate (Hueting and Tempest, 1979;Papagianni et al, 1999).…”