Catherine Couriol

Growth of Geotrichum candidum and Penicillium camembertii in liquid media in relation with the consumption of carbon and nitrogen sources and the release of ammonia and carbon dioxide

The growth of the filamentous fungi Geotrichum candidum and Penicillium camembertii on peptones as a sole carbon and nitrogen source, and in the presence of a second carbon source, lactic acid, have been compared. On both media, G. candidum exhibited similar kinetics until the end of growth, since it preferentially metabolized peptones as a carbon source, and lactic acid only for cellular maintenance during stationary phase. Growth of G. candidum was then nitrogen limited (peptones). On the contrary, fewer amino acids were convenient carbon sources for P. camembertii, resulting in a simultaneous consumption of peptones and lactic acid, and a cessation of growth due to the complete consumption of lactic acid. Morever, a lower amount of ammonia was produced since this metabolite resulted from the deamination of only carbon and nitrogen source amino acids. The production of ammonia induced an alkalinization of the broth (from 4.5 to 7.1). Morever, it was demonstrated that lactic acid consumption contributed also to media alkalinization (final pH 8.4). In absence of lactic acid, the medium contained a lower amount of available carbon, resulting in the absence of stationary state, deceleration growth phase was immediately followed by the death phase.

A New Model for the Reconstruction of Biomass History from Carbon Dioxide Emission during Batch Cultivation of Geotrichum candidum.

A non-structured model has been developed to describe the CO2 emission during growth of Geotrichum candidum on a lactate + peptone-based liquid medium. From the nitrogen and carbon mass balances, it was shown that about 50% of the total CO2 released was from the metabolism of the energy supply for biosynthesis, and the remaining from that for maintenance; thus, CO2 production was considered to be partially associated with growth. The model fitted the experimental data as long as a net growth was observed (0-50 h). The coefficients for growth- and non-growth-associated CO2 production were A = 0.646 (dimensionless) and B = 0.017 h(-1), respectively. From the coefficients of the model and the CO2 history data, the biomass kinetics has been reconstructed, and the calculated biomass concentrations agree fairly well with the experimental data. From this, measurement of the CO2 evolved may be used as an indirect and non-intrusive method of monitoring fungal growth during the first 50 h of cultivation.

Absorption and biodegradation of hydrophobic volatile organic compounds: determination of Henry's constants and biodegradation levels.

Biodegradation of three volatile organic compounds (VOCs) was studied. Toluene, dimethylsulphide (DMS), and dimethyldisulphide (DMDS) were introduced into flasks filled with emulsions of Di-2-EthylHexylAdipate (DEHA) in water, containing biomass (activated sludge). The VOC concentrations were analysed in the gas, organic and aqueous phases, and compared to the initial VOC quantities introduced in order to deduce their consumption by biomass. Toluene and DMDS were completely consumed, and then removed from the gas and the organic phases, except when DEHA and water are in the same volume ratio, which appears to be extreme environmental conditions for bacterial growth. The high DMS volatility resulted in an important gas loss, leading to a lower amount of DMS available for activated sludge growth. For all the VOC experiments, some components, characteristics of the DEHA degradation, including 2-ethylhexanal, 2-ethylhexanol, 2-ethylhexanoic acid and adipic acid, were identified.

Carbon and nitrogen yields during batch cultures of Geotrichum candidum and Penicillium camembertii

Batch cultures of Geotrichum candidum and Penicillium camembertii were carried out on peptones as carbon and nitrogen source and in the presence of lactate as a second carbon source. Unless growth ceased, carbon and nitrogen yields remained constants, except yields involving lactate consumption by G. candidum, since this fungus preferentially metabolized peptones as a carbon source. For both fungi, nearly 40% of the available carbon was metabolized for cellular biosynthesis and the remainder (about 60%) as carbon dioxide, for the energy supply of both biosynthesis and viable cell maintenance. Moreover, in relation to their carbon content, amino acids contain excess nitrogen, which was released as ammonium. From all these, the yields of ammonium nitrogen on cellular nitrogen were in all cases higher than 1, and were especially high when the medium contained only peptones as a carbon source, 4.4 and 5.7 for G. candidum and P. camembertii respectively. Indeed, in this case, the excess nitrogen was especially pronounced.