Carbon and nitrogen substrates consumption, ammonia release and proton transfer in relation with growth of Geotrichum candidum and Penicillium camemberti on a solid medium.

It is difficult to determine fungal biomass growing on a solid medium directly. Therefore, indirect ways of measuring this growth have to be used instead. For this purpose, the kinetics of growth, of substrate consumption and of release of metabolites must be correlated. This has been carried out for Geotrichum candidum and Penicillium camemberti growing on a gelified lactic acid+peptone medium. Peptone was shown to be preferred by G. candidum as a carbon and energy source, in contrast to the behaviour observed for P. camemberti. At the end of growth, G. candidum released about three times more ammonia than P. camemberti. In both cases, the total number of protons consumed during growth was close to the sum of the number of moles of metabolized lactic acid and formed ammonia. During the main part of growth, constant biomass on substrate yields (peptone, lactic acid) was observed for both microorganisms. Therefore, in pure solid cultures, the biomass concentration of both species could be deduced either from DeltapH or from the reduction of substrates. From the above, an estimate of G. candidum biomass in mixed culture could be derived from the determination of ammonia release.