Effect of amino acids on red pigments and citrinin production in Monascus ruber.

Amino acids were used as sole nitrogen sources to examine their effects on the production of water-soluble red pigments and citrinin by Monascus ruber ATCC 96218 cultivated on chemically defined media. In general, when glycine, tyrosine, arginine, serine, or histidine were used as sole nitrogen sources, they favored the production of red pigments, and restricted the synthesis of the mycotoxin. In contrast, the production of citrinin was enhanced in media supplemented with either glutamate, alanine, or proline. Histidine was found to be the most valuable amino acid as it resulted in the highest production of red pigments and almost completely eliminated the formation of mycotoxin.

Oxygen transfer in intensive microbial culture.

Oxygen transfer performances in intensive microbial cultures are compared with those occurring in coalescing and non-coalescing mineral media. E. coli fed-batch cultures are carried out in a 22 L bioreactor. Biomass concentrations of 80 g(DW) L(-1) are reached, with oxygen consumption rates of up to 0.6 mol L(-1) h(-1). To achieve these high transfer performances, dissipated power e reaches 35 kW m(-3). The hold-up in the culture broth and in the corresponding supernatant matches the non-coalescing mineral medium. Oxygen transfer coefficients, K (L) a in mineral media, and K (T) in the culture broth, are compared. K (T), calculated online from a gas balance method, excesses 1 s(-1). Yet, for given values of e, K (T) is 4-8 times lower than K (L) a determined in the non-coalescing mineral medium. The cell activity modifies the chemical medium properties and reduces the oxygen transfer conductance, as in a non-coalescing ionic medium containing surfactant.

Oleic acid delays and modulates the transition from respiratory to fermentative metabolism in Saccharomyces cerevisiae after exposure to glucose excess.

This work aimed to study the transition from respiratory to fermentative metabolism in Saccharomyces cerevisiae CEN.PK 113-7D and more specifically to evaluate the implication of the acetyl-coenzymeA-derived carbon transport from cytosol to mitochondria in the onset of the metabolic shift. The strategy consisted in introducing, during aerobic glucose-limited chemostat (D = 0.16 h(-1)), [corrected] a local perturbation around the step to be studied by the addition of cosubstrate and in analyzing the consequences of such a perturbation on the metabolic transition. Oleic acid and L: -carnitine were among the tested cosubstrates because they were known to stimulate enzymes implicated in the acetyl-coenzymeA transport between the different cell compartments, such as the carnitine acetyl transferases. The metabolic transition was then comparatively quantified in sole glucose and in glucose/oleic acid chemostats in presence/absence of L: -carnitine after a pulse of glucose. Feeding the culture with oleic acid (D (ole) = 0.0041 and 0.0073 h(-1)) [corrected] led to a delay in the onset of the metabolic shift (up to 15 min), a 33% decrease in the ethanol production and a redirection of the carbon flux toward biomass production. The data clearly showed a modulation of the carbon distribution among respiration and fermentation, in favor of a decrease in the "short-term" Crabtree effect by the oleic acid.

Kinetic modelling of Lactobacillus casei ssp. rhamnosus growth and lactic acid production in batch cultures under various medium conditions.

Enrichment of medium with yeast extract and tryptone increased growth and lactic acid production in batch cultures of Lactobacillus casei ssp. rhamnosus. A reliable kinetic model that explicitly expresses the strong relationship between microbial growth, lactic acid production and medium enrichment is provided and validated using experimental data obtained with six different medium compositions.

Role of reserve carbohydrates in the growth dynamics of Saccharomyces cerevisiae.

The purpose of this study was to explore the role of glycogen and trehalose in the ability of Saccharomyces cerevisiae to respond to a sudden rise of the carbon flux. To this end, aerobic glucose-limited continuous cultures were challenged with a sudden increase of the dilution rate from 0.05 to 0.15 h(-1). Under this condition, a rapid mobilization of glycogen and trehalose was observed which coincided with a transient burst of budding and a decrease of cell biomass. Experiments carried out with mutants defective in storage carbohydrates indicated a predominant role of glycogen in the adaptation to this perturbation. However, the real importance of trehalose in this response was veiled by the unexpected phenotypes harboured by the tps1 mutant, chosen for its inability to synthesize trehalose. First, the biomass yield of this mutant was 25% lower than that of the isogenic wild-type strain at dilution rate of 0.05 h(-1), and this difference was annulled when cultures were run at a higher dilution rate of 0.15 h(-1). Second, the tps1 mutant was more effective to sustain the dilution rate shift-up, apparently because it had a faster glycolytic rate and an apparent higher capacity to consume glucose with oxidative phosphorylation than the wild type. Consequently, a tps1gsy1gsy2 mutant was able to adapt to the dilution rate shift-up after a long delay, likely because the detrimental effects from the absence of glycogen was compensated for by the tps1 mutation. Third, a glg1Deltaglg2Delta strain, defective in glycogen synthesis because of the lack of the glycogen initiation protein, recovered glycogen accumulation upon further deletion of TPS1. This recovery, however, required glycogen synthase. Finally, we demonstrated that the rapid breakdown of reserve carbohydrates triggered by the shift-up is merely due to changes in the concentrations of hexose-6-phosphate and UDPglucose, which are the main metabolic effectors of the rate-limiting enzymes of glycogen and trehalose pathways.

Why and how membrane bioreactors with unsteady filtration conditions can improve the efficiency of biological processes.

A membrane bioreactor (MBR), an association of a bioreactor with a crossflow filtration unit, enables continuous processes with total cell retention within the reactor to be realized. Provided that high dilution rates can be applied and that inhibition processes are avoided, very high biomass concentrations can be reached, thereby improving the volumetric productivities. These membrane bioreactors have been successfully applied to various microbial bioconversion, such as alcoholic fermentation, solvents, organic acid production, starters, and wastewater treatment. On the basis of the biological reaction characteristics and bibliographic results, the potentialities and bottlenecks of this methodology are discussed. Depending on the application, it is shown how the performance of the membrane bioreactor can be enhanced by acting either on the biological reaction achievement, by controlling the balance between cell growth and death, or on the dilution rate, by increasing the permeate flux through the filtration unit. This discussion is based on results obtained in specific biological treatments applied to polluted liquid and gas.

SCP production from organic acids with Candida utilis

O crescimento de Candida utilis foi estudado em culturas em batelada e em culturas contínuas tendo como fonte de carvbono ácido acético, ácido propiônico e ácido butírico. Estes compostos mostraram ser tóxicos e altamente inibidores em concentraçöes relativamente baixas. O rendimento de biomassa diminue à medida em que a concentraçäo do substrato aumento. Estudou-se igualmente a manutençäo celular em ácidos orgânicos. O microrganismo pode utilizar de 5 a 44,8% de substrato para para manutençäo. Candida utilis desenvolveu-se bem em efluentes ácidos provenientes de fermentaçäo acidogênica. Mostrou-se que o uso destes efluentes para produçäo de SCP (proteína de organismo unicelulares) é possível e interessante

Tecnologías alternativas para a fermentaçäo alcoólica em Saccharomyces cerevisiae / Alternative tecnology for alcoholic fermentation by Saccharomyces cerevisiae

Apresenta-se uma revisäo sobre os parâmetros e técnicas da fermentaçäo alcoólica em Saccharomyces cerevisiae. Säo abordados processos de fermentaçäo em regime descontínuo (convencional e alimentado) e contínuo (fermentaçäo extrativa, com reciclagem celular, com floculaçäo de leveduras, com imobilizaçäo celular, acoplada a filtros de membranas e de fibras parosas). O processo descontínuo convencional pode levar a altos rendimentos, mas a produtividade é muito baixa, dificilmente ultrapassando 0,5 g etanol/l.h. O teor máximo no meio situa-se em geral na baixa de 80-90 g/l. Pelo processo descontínuo alimentado atenua-se a inibiçäo pelo substrato, o que permite elevar o teor de etanol no masto fermentado, além de melhorar a produtividade. As técnicas contínuas, embora ainda via de regra onerosas para a produçäo industrial de etanol em larga escala, têm tido avanças tecnológicas relevantes. Além de outras vantagens, o principal trunfo é o aumento acentuado da produtividade, que pode chegar a 80 g etanol/l.h., ou mais