RESUMO
In submerged cultures performed in synthetic medium containing glucose and glutamate, the filamentous fungus Monascus ruber produced a red pigment and a mycotoxin, citrinin. In oxygen-limiting conditions, the production of these two metabolites was growth-associated, as was the production of primary metabolites. In oxygen-excess conditions, the profile of citrinin production was typical of a secondary metabolite, since it was produced mostly during the stationary phase. In contrast, the production of the pigment decreased rapidly throughout the culture, showing a profile characteristic of an inhibitory mechanism. The organic acids produced during the culture, L-malate and succinate, were shown to be slightly inhibitory against pigment production, while citrinin production was unaffected. However, this inhibition could not account for the observed profile of pigment production in batch cultures. Other dicarboxylic acids such as fumarate or tartrate showed a similar effect to that provoked by malate and succinate as regards pigment production. It was concluded that the decrease in red pigment production during the culture was due to the inhibitory effect of an unknown product whose accumulation was favored in aerobic conditions.
RESUMO
Simple and reliable protocols are described for an extensive analysis of metabolites in extracts from different biological sources. The separation was performed by high performance ionic-exchange chromatography (HPIC) at alkaline pH using two types of chromatography columns and two detection methods. Organic acids and inorganic anions were separated on an ionPac AS11 column using a 0.5 to 35 mM Na0H gradient. Detection limits in the range of milligrams per liter were achieved by use of a conductivity detector equipped with an anion self-regenerating suppressor. Twelve phosphorylated compounds belonging to the glycolytic and the pentose phosphate pathways could be resolved on a CarboPac PA1 column using a Na0H/Na-acetate gradient. Quantification was achieved by pulsed amperometry with detection limits in the micromolar range. Cell extracts obtained by extraction in boiling buffered ethanol described previously could be directly injected onto HPIC columns for the separation of metabolites because the extraction procedure affected neither the retention time nor the stability of most of the metabolites, and yielded very clean chromatograms. These improved protocols were applied for a dynamic analysis of intracellular metabolites in Saccharomyces cerevisiae in response to a glucose pulse.
RESUMO
The growth and metabolic behaviour of the filamentous fungus Monascus ruber were studied in submerged cultures under various aeration and agitation conditions. Improving the oxygen supply, by increasing either the air input or the agitation speed, resulted in modified metabolism: the biomass yield, the consumption of the nitrogen source (monosodium glutamate), and the production of secondary metabolites (red pigment and citrinin) all increased. However, the citrinin production increased more than that of the red pigment. In consequence, a low oxygen transfer coefficient was required to improve the red pigment/citrinin production ratio. Copyright 1999 John Wiley & Sons, Inc.
