BACKGROUND: This work examines the metabolic behaviour of amino acids during Geotrichum candidum growth, in the presence of a primary carbon source like glucose. Amino acids were characterized based on their carbon assimilation and dissimilation by G. candidum, in the presence of glucose as the limiting substrate. RESULTS: The first group (Cys, His, Phe, Thr and Trp) was only used as nitrogen sources by G. candidum, with glucose being the carbon and energy source. Glucose repression was shown for the rest of the amino acids, since only after glucose depletion amino acids from the second group (Gly, Lys, Met, Val) were dissimilated for energy supply by oxidation into CO2, while those from the third group (Ala, Arg, Asp, Glu, Len, Pro And Ser) were assimilated as carbon sources (and additionally used as nitrogen sources), leading to a diauxic growth. CONCLUSION: This energy-saving response was not previously shown for the second fungus involved in ripening of soft white cheese -P. camembertii - leading to simultaneous use of some amino acids and glucose as carbon and energy sources, and hence lower growth rates than those recorded during G. candidum growth. (C) 2007 Society of Chemical Industry.