Relationships Between Proton Extrusion and Fluxes of Ammonium Ions and Organic Acids in Penicillium cyclopium

Abstract

~ ~ ~~Acidification observed in cultures of Penicillium cyclopium was mostly due to the extrusion of protons into the medium. In the absence of NH,+ , protons were extruded together with citrate.The citric acid thus produced underwent a dynamic equilibrium of continuous efflux and uptake, which was shifted towards the latter at decreasing glucose concentrations. In cultures supplied with NH,+ and glucose a stoichiometric coupling of H + excretion with NH,+ uptake was observed. If the protons excreted were not absorbed by external buffers (e.g. tartrate ions), the pH of the medium dropped to below 2, thereby exceeding the capacity of the cells to maintain their internal pH. The decrease of intracellular pH was accompanied by the cessation of NH,+ uptake, H + extrusion and growth. In the presence of tartrate ions the NH,+/H+ exchange proceeded until the glucose concentration of the medium dropped below 25 mM. Here, the external pH was kept above 3, without seriously affecting the intracellular pH. After termination of H + extrusion an appreciable amount of NH,+ was taken up together withAbbreviations: pH,,,,, intracellular pH ; pH,,, , extracellular pH.

Influence of medium components and metabolic inhibitors on citric acid production by Penicillium simplicissimum

“…This acidification was stoichiometric (1 : 1) with the uptake of ammonium. A similar acidification behaviour has been described for P. cyclopium in a non-buffered medium with ammonium chloride as nitrogen source (Roos & Luckner, 1984). P. simplicissimurn formed about 2 g dry wt l-' during these 3 d.…”

“…A variety of extracellular factors may stimulate a fungal hypha to excrete large amounts of citric acid, for instance: (i) a deficiency of trace elements combined with a low extracellular pH (Kubicek & Rohr, 1986); (iij the presence of a specific nitrogen source; and (iii) the presence of a (high) extracellular buffering capacity (Roos & Luckner, 1984). These results show that with P.…”

Isolation and Culture of a Thermophilic Fungus, Melanocarpus albomyces, and Factors Influencing the Production and Activity of Xylanase

“…The pH of these media either did not change significantly during growth (asparagine and urea), or it rose to 7.5 (NaN03). These results suggested that the fungus did not tolerate acidic conditions which presumably resulted from the absorption of NHZ and counter-transport of H+, as has been shown for Penicillium cyclopium (Roos & Luckner, 1984). Urea was chosen as the nitrogen source for subsequent culture as it produced satisfactory yields and the mycelia grew as small pellets (approximately 1-3 mm in diameter).…”

Evaluation of yield and quality parameters of phosphorous-solubilizing and N-fixing bacteria inoculated in wheat (Triticum aestivum L.)

“…phosphaticum in mineral phosphate solubility is well known (Lach et al, 1990;Vazquez et al, 2000). Phosphate solubility is related to organic acid and proton release and consequent NH 4 assimilation (Kucey, 1983;Roos and Luckner, 1984;Asea et al, 1988;Abd-Alla, 1994;Illmer et al, 1995;Whitelaw, 2000). Such relationships may be relevant to phosphatase enzyme release.…”