Geotrichum candidum and Penicillium camembertii were cultivated in pure and mixed cultures on glutamate- and lactate-based medium. In pure culture, P. camembertii assimilated simultaneously glutamate, as a nitrogen and carbon source for biosynthesis, and lactate as an energy source. On the contrary, G. candidum grew on glutamate alone. The mixed culture led to higher growth rates and then higher rates of substrate consumption and metabolite production than each pure culture; however, the behaviour recorded was similar to that observed during G. candidum pure culture, in particular the absence of lactate assimilation during growth, illustrating a commensalism between both species. The presence of G. candidum induced a form of "competition" and then a better assimilation by P. camembertii of the sole nitrogen source, glutamate, which was therefore used as an energy source in addition to be a carbon (and nitrogen) source. Lactate was only used for energy supply during stationary state, as also recorded during G. candidum pure culture. (c) 2006 Elsevier Ltd. All rights reserved.