Fermentations of fructo-oligosaccharides and their components by Bifidobacterium infantis ATCC 15697 on batch culture in semi-synthetic medium

AIMS: To compare the physiological behaviour of Bifidobacterium infantis ATCC 15697 growing on synthetic oligofructose or its components. METHODS AND RESULTS: The studies were carried out in regulated or non-regulated batch cultures on semi-synthetic media. Differences between the carbohydrate utilization patterns with glucose, fructose, sucrose and fructo-oligosaccharides (FOS) were determined. Glucose was the preferred substrate for growth and biomass production, whereas fructose was the best for lactate and acetate production. With sucrose, biomass production reached the level obtained with glucose, whereas with FOS, more metabolites were produced, as with fructose. In a mixture of FOS, the shorter saccharides were used first and fructose was released in the medium. Fructofuranosidase, an enzyme necessary to hydrolyse FOS, was inducible by fructose. CONCLUSION: Glucose contained in FOS and sucrose might sustain growth and cell production, while fructose might enable the production of major metabolites. SIGNIFICANCE AND IMPACT OF THE STUDY: A better understanding of the bifidogenic nature of oligofructose has been gained.     

AUTOTROPHIC AND HETEROTROPHIC NUTRITIONAL BUDGET OF SALT MARSH EPIPHYTIC ALGAE1

This paper addresses the nutrition and relative importance of primary production to heterotrophy of select unicellular green algae and diatoms from the same assemblage. Algal growth responses to nutrient additions varied widely. Such responses included: inhibition and enhancement of growth by amino acid additions: nonstimulation or inhibition by most sugars 10 mM concentration; glucose stimulation of 6 and inhibition of 3 species; fructose inhibition of 6- and 3- fold stimulation of one species; stimulation of most species by a vitamin mixture, some natural products, metabolite mixtures, etc. Photoassimilation of glucose and aculeate in 8 of 12 species occurred. Nine of 12 species took up only a fraction of the total carbon fixed as organic substrate. Enhancement of photosynthesis by glucose and inhibition by acetate was common. The data suggest that attached littoral and shoal marine algal assemblages may play mixed trophic roles lower levels of the detrital food web.     

Yarrowia lipolytica as a potential producer of citric acid from raw glycerol

AIMS: To study the biochemical response of Yarrowia lipolytica LGAM S(7)1 during growth on raw glycerol (the main by-product of bio-diesel production units) in order to produce metabolic products of industrial significance. METHODS AND RESULTS:Yarrowia lipolytica was cultivated on raw glycerol or glucose in flasks. Although nitrogen-limited media were employed, growth was not followed by production of reserve lipid. Nitrogen limitation led to citric acid excretion. Growth and citric acid production parameters on glycerol were similar to those obtained on glucose. When high initial glycerol media were used, citric acid up to 35 g l(-1) (yield 0.42-0.44 g acid g(-1) glycerol consumed) was produced. CONCLUSIONS: Raw glycerol was an adequate substrate for Y. lipolytica. Growth was not followed by reserve lipid accumulation, but amounts of citric acid were produced. SIGNIFICANCE AND IMPACT OF THE STUDY: Raw glycerol is an industrial feedstock appearing in increasing quantities as the main by-product of bio-diesel production facilities. The present study describes an alternative way of glycerol valorization, with the production of remarkable amounts of citric acid, in addition to its main valorization way (production of 1,3-propanediol by bacteria).     

Structure, production characteristics and fungal antagonism of tensin - a new antifungal cyclic lipopeptide from Pseudomonas fluorescens strain 96.578

AIM: To study the antagonistic activity by Pseudomonas fluorescens strain 96.578 on the plant pathogenic fungus Rhizoctonia solani. METHODS AND RESULTS: Strain 96.578 produced a new cyclic lipopeptide, tensin. High tensin production per cell was detected in liquid media with glucose, mannitol or glutamate as growth substrate while fructose, sucrose and asparagine supported low production. Tensin production was nearly constant in media with different initial C levels, while low initial N contents reduced production. When applied to sugar beet seeds, strain 96.578 produced tensin during seed germination. When challenged with strain 96.578 or purified tensin, Rhizoctonia solani reduced radial mycelium extension but increased branching and rosette formation. CONCLUSION: The antagonistic activity of strain 96.578 towards Rhizoctonia solani was caused by tensin. SIGNIFICANCE AND IMPACT OF THE STUDY: When coated onto sugar beet seeds, tensin production by strain 96.578 could be of significant importance for inhibition of mycelial growth and seed infection by Rhizoctonia solani.     

Regulation of rat liver 4-hydroxy-2-ketogrlutarate aldolase

The possibility is examined that 4-hydroxy-2-ketoglutarate aldolase (4-hydroxy-2-ketoglutarate glyoxylatelyase, EC 4.1.3.16), the last step in hydroxyproline catabolism is regulated by intermediates of gluconeogenesis. inhibition of isolated 4-hydoxy-2-ketoglutarate aldolase was examined using dual inhibition studies. It was found that the enzyme exhibits synergistic inhibition by oxaloacetate and pyruvate, but only when the substrate concentration is low. At substrate concentrations approaching saturation, the inhibition by the oxaloacetate and pyruvate becomes additive. These results are discussed in terms of possible control of the use of carbon from hydroxyproline breakdown in glucose production.     

Studies on growth and metabolism of Oenococcus oeni on sugars and sugar mixtures

AIMS: To study the effect of sugars and sugar mixtures on the growth kinetics of Oenococcus oeni NCIMB 11648 in batch culture with the aim of producing a high cell productivity system for starter cultures. METHODS AND RESULTS: The growth of O. oeni was investigated on single sugars (glucose, fructose or sucrose) and their mixtures (glucose-fructose, glucose-sucrose or fructose-sucrose). Better growth was obtained on sugar mixtures compared with growth on a single sugar. The production system of O. oeni biomass was investigated in batch culture with or without pH control with respect to kinetics, specific growth rate and biomass yield. The effect of pH and substrate concentration on fermentation balances and ATP yield were determined. The optimal growth of O. oeni was achieved on the glucose-fructose mixture (9 g l(-1), 1 : 1) at pH 4.5 and 25 degrees C with pH control, with highest cell volumetric productivity (7.9 mg cell l(-1) h(-1)), biomass yield (0.041 g cell g(-1) sugar) and specific growth rate (0.066 h(-1)). CONCLUSIONS: The limitations to the growth of O. oeni were pH and inhibition by end product resulting in poor utilization of the medium with low cell yields. The cell productivity of the system can be improved by the appropriate use of mixed sugar growth medium. SIGNIFICANCE AND IMPACT OF THE STUDY: This study uniquely showed that appropriate sugar mixtures with the correct environmental conditions can significantly improve the productivity of O. oeni cultures.     

Regulation of rat liver 4-hydroxy-2-ketoglutarate aldolase

The possibility is examined that 4-hydroxy-2-ketoglutarate aldolase (4-hydroxy-2-ketoglutarate glyoxylatelyase, EC 4.1.3.16), the last step in hydroxyproline catabolism is regulated by intermediates of gluconeogenesis. Inhibition of isolated 4-hydoxy-2-ketoglutarate aldolase was examined using dual inhibition studies. It was found that the enzyme exhibits synergistic inhibition by oxaloacetate and pyruvate, but only when the substrate concentration is low. At substrate concentrations approaching saturation, the inhibition by the oxaloacetate and pyruvate becomes additive. These results are discussed in terms of possible control of the use of carbon from hydroxyproline breakdown in glucose production.     

Metabolic load of recombinant protein production: inhibition of cellular capacities for glucose uptake and respiration after induction of a heterologous gene in Escherichia coli

The strong expression of recombinant proteins in bacteria affects the primary carbon and energy metabolism resulting in growth inhibition and acetate formation. By applying glucose pulses to fed-batch fermentations performed for production of a heterologous (alpha-glucosidase in Escherichia coli, we show that the induction of the recombinant gene strongly inhibits the maximum specific uptake capacities for glucose and the respiration capacity. The accumulation of glucose in the fermentation medium promotes the growth of plasmid-free cells. These inhibition effects are well described by including the kinetics of product formation into a recently published dynamic model (Lin et al. [2001] Biotechnol Bioeng 73:349-357). The new model also includes the population characteristics and gives a good fit to the measured data describing growth, production, substrate consumption, by-product formation, and respiration.     

Modelling the growth kinetics of <Emphasis Type="Italic">Kocuria marina</Emphasis> DAGII as a function of single and binary substrate during batch production of β-Cryptoxanthin

In the present investigation, growth kinetics of Kocuria marina DAGII during batch production of β-Cryptoxanthin (β-CRX) was studied by considering the effect of glucose and maltose as a single and binary substrate. The importance of mixed substrate over single substrate has been emphasised in the present study. Different mathematical models namely, the Logistic model for cell growth, the Logistic mass balance equation for substrate consumption and the Luedeking–Piret model for β-CRX production were successfully implemented. Model-based analyses for the single substrate experiments suggested that the concentrations of glucose and maltose higher than 7.5 and 10.0 g/L, respectively, inhibited the growth and β-CRX production by K. marina DAGII. The Han and Levenspiel model and the Luong product inhibition model accurately described the cell growth in glucose and maltose substrate systems with a R ² value of 0.9989 and 0.9998, respectively. The effect of glucose and maltose as binary substrate was further investigated. The binary substrate kinetics was well described using the sum-kinetics with interaction parameters model. The results of production kinetics revealed that the presence of binary substrate in the cultivation medium increased the biomass and β-CRX yield significantly. This study is a first time detailed investigation on kinetic behaviours of K. marina DAGII during β-CRX production. The parameters obtained in the study might be helpful for developing strategies for commercial production of β-CRX by K. marina DAGII.     

Effects of inhibition and repression on the utilization of substrates by heterogeneous bacterial communities

This investigation attempts to evaluate to what extent enzyme inhibition and repression by metabolites, indigenous to the cell, are significant phenomena in natural microbial communities. Three case histories of the kinetics of substrate utilization and growth in multisubstrate media by heterogeneous bacterial populations are presented: (i) concurrent substrate utilization and growth on both substrates simultaneously (glucose plus benzoate); (ii) sequential substrate elimination accompanied by diauxic growth as a result of inhibition of enzyme activity (glucose plus galactose); (iii) sequential substrate utilization accompanied by diauxic growth caused by repression of enzyme formation (glucose plus l-phenylalanine, benzoate plus l-phenylalanine). It is shown that enzyme inhibition was observed in two-substrate media as well as in multisubstrate media and was maintained at low substrate concentrations (few milligrams per liter). A special attempt has been made to maintain the diversity of the experimental microbial population during the adaptation and enrichment period. All substrates were determined with sensitive analytical methods specific for the individual substrates. The results obtained confirm that catabolite repression and the resulting sequential substrate utilization are observed in heterogeneous bacterial populations.     

Nutritional requirements and simplified cultivation medium to study growth and energetics of a sourdough lactic acid bacterium Lactobacillus fermentum Ogi E1 during heterolactic fermentation of starch

AIMS: Nutritional requirements of Lactobacillus fermentum Ogi E1 were studied in order to define a simplified fermentation medium. METHODS AND RESULTS: When grown with MRS-medium in 2l bioreactors, a biphasic pattern of growth and metabolite production was observed. Study of nutritional requirements resulted in a simplified medium (SYAM) that allowed, under anaerobiosis, similar results to be obtained as in MRS medium, but without biphasic fermentation kinetics. The best substrates for both growth and amylase production were starch and maltose. Although melibiose, raffinose, fructose, sucrose and glucose also supported growth, lower amylase activity was observed. CONCLUSION: The physiology of the strain can be investigated with SYAM medium, using either starch or maltose as substrate. The strain also presented potential for alpha-galactoside fermentation. SIGNIFICANCE AND IMPACT OF THE STUDY: Lactobacillus fermentum was one of the dominant bacteria of African maize dough fermentations. Amylolytic strains with activity against other compounds (i.e. raffinose) suggested a potential to be used as starter for cereal fermentation.     

Kinetic modeling of Candida shehatae ATCC 22984 on xylose and glucose for ethanol production

Candida shehatae ATCC 22984, a xylose-fermenting yeast, showed an ability to produce ethanol in both glucose and xylose medium. Maximum ethanol produced by the yeast was 48.8?g/L in xylose and 52.6?g/L in glucose medium with ethanol yields that varied between 0.3 and 0.4?g/g depended on initial sugar concentrations. Xylitol was a coproduct of ethanol production using xylose as substrate, and glycerol was detected in both glucose and xylose media. Kinetic model equations indicated that growth, substrate consumption, and product formation of C. shehatae were governed by substrate limitation and inhibition by ethanol. The model suggested that cell growth was totally inhibited at 40?g/L of ethanol and ethanol production capacity of the yeast was 52?g/L, which were in good agreement with experimental results. The developed model could be used to explain C. shehatae fermentation in glucose and xylose media from 20 to 170?g/L sugar concentrations.     

Substrate and product inhibition kinetics in succinic acid production by Actinobacillus succinogenes

The inhibition of substrate and products on the growth of Actinobacillus succinogenes in fermentation using glucose as the major carbon source was studied. A. succinogenes tolerated up to 143 g/L glucose and cell growth was completely inhibited with glucose concentration over 158 g/L. Significant decrease in succinic acid yield and prolonged lag phase were observed with glucose concentration above 100 g/L. Among the end-products investigated, formate was found to have the most inhibitory effect on succinic acid fermentation. The critical concentrations of acetate, ethanol, formate, pyruvate and succinate were 46, 42, 16, 74, 104 g/L, respectively. A growth kinetic model considering both substrate and product inhibition is proposed, which adequately simulates batch fermentation kinetics using both semi-defined and wheat-derived media. The model accurately describes the inhibitory kinetics caused by both externally added chemicals and the same chemicals produced during fermentation. This paper provides key insights into the improvement of succinic acid production and the modelling of inhibition kinetics.     

Nutrient requirements of Bacillus anthracis strains and the growth characteristics of strain STI-1 in batch cultivation on synthetic broths

A synthetic culture medium is proposed. This medium satisfies the nutritional requirements of most cultivated strains under study by a single amino acid: valine. The possibility of detecting strains with other nutritional requirements has been shown. The determination of LD50 in white mice has revealed no differences between the virulence of valine-dependent strains and that of strains with other nutritional requirements. During the batch cultivation of strain STI-1 in a liquid medium glucose shows the effect of substrate limitation and inhibition. The optimum concentration of glucose can be different, depending on the composition of the medium. The influence of different amino acids, the sources of carbon and energy, and nitrogen on the growth of the strain is evaluated.     

Substrate inhibition kinetics of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> in fed-batch cultures operated at constant glucose and maltose concentration levels

Fed-batch culture is the mode of operation of choice in industrial baker’s yeast fermentation. The particular mode of culture, operated at stable glucose and maltose concentration levels, was employed in this work in order to estimate important kinetic parameters in a process mostly described in the literature as batch or continuous culture. This way, the effects of a continuously falling sugar level during a batch process were avoided and therefore the effects of various (stable) sugar levels on growth kinetics were evaluated. Comparing the kinetics of growth and the inhibition by the substrate in cultures grown on glucose, which is the preferential sugar source for Saccharomyces cerevisiae, and maltose, the most common sugar source in industrial media for baker’s yeast production, a milder inhibition effect by the substrate in maltose-grown cells was observed, as well as a higher yield coefficient. The observed sugar inhibition effect in glucostat cultures was taken into account in modeling substrate inhibition kinetics. The inhibition coefficient K _i increased with increasing sugar concentration levels, but it appeared to be unaffected by the type of substrate and almost equal for both substrates at elevated concentration levels.     

Modeling of Xanthophyllomyces dendrorhous growth on glucose and overflow metabolism in batch and fed-batch cultures for astaxanthin production

An astaxanthin-producing yeast Xanthophyllomyces dendrorhous ENM5 was cultivated in a liquid medium containing 50 g/L glucose as the major carbon source in stirred fermentors (1.5-L working volume) in fully aerobic conditions. Ethanol was produced during the exponential growth phase as a result of overflow metabolism or fermentative catabolism of glucose by yeast cells. After accumulating to a peak of 3.5 g/L, the ethanol was consumed by yeast cells as a carbon source when glucose in the culture was nearly exhausted. High initial glucose concentrations and ethanol accumulation in the culture had inhibitory effects on cell growth. Astaxanthin production was partially associated with cell growth. Based on these culture characteristics, we constructed a modified Monod kinetic model incorporating substrate (glucose) and product (ethanol) inhibition to describe the relationship of cell growth rate with glucose and ethanol concentrations. This kinetic model, coupled with the Luedeking-Piret equation for the astaxanthin production, gave satisfactory prediction of the biomass production, glucose consumption, ethanol formation and consumption, and astaxanthin production in batch cultures over 25-75 g/L glucose concentration ranges. The model was also applied to fed-batch cultures to predict the optimum feeding scheme (feeding glucose and corn steep liquor) for astaxanthin production, leading to a high volumetric yield (28.6 mg/L) and a high productivity (5.36 mg/L/day).     

Kinetics of the selective fermentation of glucose from glucose/fructose mixtures using Saccharomyces cerevisiae ATCC 36859

The kinetics of batch fermentation during the growth of S. cerevisiae ATCC 36859 was studied in various glucose/fructose mixtures. It was found that the growth is inhibited equally by glucose and fructose even though fructose is not consumed to any large extent by the yeast under the conditions tested here. The inhibition of growth by the substrate and ethanol is represented by linear equations. These equations were combined with the MONOD expression in order to formulate equations for the biomass growth, glucose and fructose consumption and ethanol production. Parameter estimates were obtained by fitting these equations to batch fermentation data and so developing models which indicate that the growth is completely inhibited when 62 g/l ethanol is produced by the yeast, while glucose consumption and ethanol production continue up to an ethanol concentration of 152 g/l. Products containing a high concentration of fructose are best produced by using a high initial biomass concentration.     

Modulation of anti-pathogenic activity in canine-derived Lactobacillus species by carbohydrate growth substrate

AIMS: To investigate the effect of various carbon sources on the production of extracellular antagonistic compounds against two Escherichia coli strains and Salmonella enterica serotype Typhimurium by three canine-derived lactobacilli strains. METHODS AND MATERIALS: Cell-free preparations, pH neutralized, were used in antibiotic disc experiments as an initial screening. The bacteria/carbohydrate combinations that showed inhibition of the growth of those pathogens, were further investigated in batch co-culture experiments. The cell-free supernatants of the cultures, that decreased the population number of the pathogens in the co-culture experiments to log CFU ml-1 相似文献   

Acetate production from lactate and glucose fermentation by Gluconobacter oxydans

Summary The production of acetate from the fermentation of lactate by Gluconobacter oxydans was studied. Batch experiments showed that glucose was the preferred substrate compared to lactate. A fed-batch culture was fed with a mixture of glucose and lactate followed by periodic addition of lactate. The maximum productivity of acetate was 0.16 g/l h but this value decreased during the fedbatch culture due to growth inhibition by acetate.