Diauxic growth of Geotrichum candidum and Penicillium camembertii on amino acids and glucose (original) (raw)
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Amino acids had previously been characterized based on their ability to be assimilated as carbon sources by Penicillium camemberti and Geotrichum candidum. For each microorganism, three groups of amino acids have been characterized, leading to four different metabolic behaviours. To describe those recorded during P. camemberti growth on an amino acid and glucose, an unstructured model had previously been developed, based on the sequential consumption of both carbon substrates; glucose first, followed after its exhaustion by the selected amino acid. Only the part of the amino acid assimilated as a carbon source for cellular biosynthesis was considered in the model, which had to be deduced from the total amino acid consumption. To avoid the use of such an indirect parameter, ammonium was considered in this work, which was produced after amino acid deamination and corresponded to the release of the excess nitrogen, since amino acids contain excess nitrogen in relation to their carbon content in fungi. The model, therefore, involved substrate carbon consumption, ammonium production, as well as biomass yield on the carbon substrate, Y X/S , and biomass yield on the produced ammonium, Y X/P. The model proved to describe satisfactorily the various metabolic behaviours recorded during P. camemberti and G. candidum growth on an amino acid and glucose.
Carbon assimilation and dissimilation during growth ofGeotrichum candidum on amino acids and glucose
Journal of Chemical Technology & Biotechnology, 2007
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 CO 2 , while those from the third group (Ala, Arg, Asp, Glu, Leu, 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.
Geotrichum candidum Geo17 was cultivated on peptones as carbon and nitrogen source, and in the presence of lactate as the second carbon source. From the analysis of the initial and final culture medium after total hydrolysis, the yield of consumption was determined for each amino acid. Amino acids have been considered a convenient carbon source for biosynthesis, while the rest of the amino acids were assumed to be used only as a nitrogen source, with the corresponding carbon released as CO 2 resulting from energy supply. Carbon mass balances confirmed this assumption. A clear differentiation between the amino acids assimilated as carbon sources and those assimilated as energy sources was therefore highlighted.
Contribution of Geotrichum candidum to the proteolysis of soft cheese
International Dairy Journal, 2006
To determine the action of the yeast Geotrichum candidum on the proteolysis of soft cheese, Camembert-type cheeses were manufactured with and without this surface flora. Casein degradation and the release of peptides and amino acids at the cheese surface were studied to assess overall proteolysis. The results showed extensive proteolytic activity at the surface of cheese with G. candidum, and suggested that G. candidum is able to contribute to both primary and secondary proteolysis. a s1 -and bA 2 -caseins were preferentially hydrolysed at the surface of cheese with G. candidum from the first week of ripening. This proteolytic activity led to the production of numerous peptides that were subsequently hydrolysed, as indicated by the large increase in the concentration of free amino acids from the second week to the end of ripening. r
Enzyme and Microbial Technology, 2005
Geotrichum candidum and Penicillium camembertii were cultivated in pure and mixed cultures on Camembert juice. This juice extracted from curd at the demoulding contains the whole substrates available for growth of surface flora in situ. A synergistic effect of G. candidum on P. camembertii growth was clearly shown in mixed culture; the enzymatic activities of G. candidum (low molecular weight peptides hydrolysis) allowed an easier assimilation of peptides and amino acids as carbon sources by P. camembertii, no other carbon sources were needed, or used only at the end of culture for cell maintenance, as was the case for citrate. A lower number of amino acids were convenient carbon sources for P. camembertii compared to G. candidum, resulting in its assimilation of lactose, lactate and citrate during pure culture, while G. candidum assimilated lactate and citrate only at the end of culture for the energy supply for cell maintenance. Peptides and amino acids metabolic behaviour was shown to be the main factor accounting for medium alkalinization, since their assimilation as carbon sources (in addition to nitrogen sources) resulted in ammonium production, which was found to be closely related to proton transfer.
The Journal of General and Applied Microbiology, 2008
The yeast Geotrichum candidum and the mould Penicillium camembertii are the two principal fungal populations responsible for changes occurring during ripening of white soft cheeses (Fox et al., 1993; Gripon, 1993). The interactions usually occurring during ripening result from their association (Corsetti et al., 2001; Roostita and Fleet, 1996), as well as an earlier medium colonization by G. candidum (Molimard et al., 1995). Viable cell number is more important in a mixed culture of both fungi, leading to an intense global metabolic activity (Molimard et al., 1995). Indeed, mixed fungal culture has been proven to improve enzyme production (Gutierrez-Correa and
Applied Microbiology and Biotechnology, 2002
Geotrichum candidum and Penicillium camembertii were cultivated on the surface of a gelified medium, simulating the composition of the aqueous phase of a Camembert cheese. The relation of their growth with substrate consumption (carbon or nitrogen), metabolite production (ammonia), or proton transfer (deduced from pH by means of the buffer capacity of the medium) was examined. The coefficients associated with cellular biosynthesis and resulting from cellular maintenance were determined. From these coefficients and the considered substrate utilization or metabolite production kinetics, the growth kinetics were reconstructed until the end of growth. The model allowed analysis of biosynthesis and cellular maintenance contributions to the considered kinetics. At the end of growth, almost all the peptone was used for G. candidum biosynthesis, while most of the lactic acid (62%) was used for cellular maintenance. P. camembertii metabolized fewer amino acids as carbon sources, resulting in use of peptone for maintenance (12%), and lactic acid (80%) for cell biosynthesis. For both microorganisms, ammonia production was growthassociated, since this production resulted from the deamination of carbon-and nitrogen-source amino acids, in close relation with peptone consumption.
Interests in Geotrichum candidum for cheese technology
International Journal of Food Microbiology, 2005
The wide genotypic and phenotypic diversity of Geotrichum candidum strains does not facilitate its classification as yeast or a yeast-like fungus that is still a matter of debate. Whatever its classification, G. candidum possesses many different metabolic pathways that are of particular interest to the dairy industry. G. candidum is of importance in the maturation of cheese, and much is known about its direct contribution to cheese ripening and flavour formation. Its diverse metabolic potential means that G. candidum can play an important role in the ripening of many soft and semi-hard cheeses and make a positive contribution to the development of taste and aroma. It may also influence the growth of other microorganisms, both valuable and detrimental. The significance of the presence of G. candidum in cheese depends on the particular type of production and on the presence of biotypes featuring specific types of metabolism. However, in situ metabolic pathways involved in cheese ripening and their regulations are mainly unknown. The information available provides a good understanding of the potential of G. candidum strains that are used in cheese manufacture, and permits a better choice of strain depending on the characteristics required. The biochemical activities of G. candidum and its application in the dairy industry are presented in this review. D
Enhanced proteolytic activities of Geotrichum candidum and Penicillium camembertii in mixed culture
Enzyme and Microbial Technology, 2006
Soft cheese ripening is mainly controlled by proteolytic activities of Geotrichum candidum and Penicillium camembertii. To investigate the proteolytic activities involved in the synergistic effect, pure and mixed cultures of both micro-organisms were performed on Camembert juice. Proteolysis monitored throughout culture using SDS-PAGE and RP-HPLC profiles, as well as free amino acids (FAAs) concentration time-courses showed that G. candidum degrades immediately large and medium peptides in FAAs, which were partly assimilated, while P. camembertii assimilated large peptides but medium and small peptides were less consumed. The similar chromatograms of the mixed and G. candidum cultures tend to demonstrate that the proteolytic activities of G. candidum dominated in the mixed culture up to 112 h. Continuous proteolysis and assimilation of peptides occurred throughout the second part of P. camembertii culture, leading to the production of FAAs. These activities allow G. candidum to have medium and small peptides to hydrolyse during the mixed culture. Because of the rapid degradation of these peptides in FAAs, no more peptides were available for P. camembertii growth, which should therefore assimilate FAAs, leading to a rapid decrease of their concentration. The synergistic effect between G. candidum and P. camembertii was therefore predominant during the second part of culture.
The Roles of Candida tropicalis Toward Peptide and Amino Acid Changes in Cheese Whey Fermentation
International Journal of Technology
Whey is a by-product of cheese processing and is comprised of nearly 90% of the milk used. The protein content in cheese whey has the potential to create peptide and amino acids which have a functional effect in biological activity. Peptides and amino acids can be produced through fermentation with Candida tropicalis into native whey from cheese whey. The study aims to determine fermentation time in producing peptide and amino acid profiling in the fermentation of native cheese whey by Candida tropicalis. Cheese whey fermented with C. tropicalis was compared to a naturally fermented cheese whey as control at an ambient temperature for 48 hours. Peptide content identified by Folin-Ciocalteu methods and the amino acid profile is determined by high performance liquid chromatography (HPLC). Fermentation results showed that the maximum content of peptides needs a 24-hour fermentation in 10.42 ppm. Peptide content decreased with further fermentation caused by the degradation of peptides into amino acids. The amino acids that increased were aspartate, glutamate, threonine, valine, isoleucine, and lysine, while those that decreased were serine, histidine, glycine, arginine, alanine, tyrosine, and methionine.