Consumption Of Nitrogen Sources Research Articles

Modeling and optimization of sporulation by Bacillus licheniformis BF-002 based on dynamics and recurrent neural networks

Bacillus licheniformis is widely utilized in disease prevention and environmental remediation. Spore quantity is a critical factor in determining the quality of microbiological agents containing vegetative cells. To improve the understanding of Bacillus licheniformis BF-002 strain culture, a hybrid model integrating traditional dynamic modeling and recurrent neural network was developed. This model enabled the optimization of carbon/nitrogen source feeding rates, pH, temperature and agitation speed using genetic algorithms. Carbon and nitrogen source consumption in the optimal duplicate batches showed no significant difference compared to the control batch. However, the spore quantity in the broth increased by 16.2% and 35.2% in the respective duplicate batches. Overall, the hybrid model outperformed the traditional dynamic model in accurately tracking the cultivation dynamics of Bacillus licheniformis, leading to increased spore production when used for optimizing cultivation conditions.

Evaluation of the Growth Performance of Microalgae Based on Fine pH Changes

Microalgae are photosynthetic microorganisms with many potential applications in the food, cosmetics, pharmaceutical and environmental industries. Currently, commercial microalgae production remains limited. Therefore, improving the growth and the culture density of the microalgae cultivation is one of the key enablers to open the way to mass production and commercialisation of these microorganisms. The effect of culture pH on the photoautotrophic growth of C. vulgaris over a large range of values has been investigated in pH-regulated cultures. For each microalgae culture, the specific growth rate, the cell density, the chlorophyll content, the intracellular carbon content and the nitrogen source consumption were monitored. Optimal growth and carbon incorporation have been observed at pH of 7.0. The fastest growth rate and highest biomass production of C. vulgaris were 0.074 h-1 and 0.896 g/L respectively. Under these conditions, a maximum carbon content of cells was 49 % (w/w).

Nitrogen sources preferences of non-Saccharomyces yeasts to sustain growth and fermentation under winemaking conditions

Wine-related non-Saccharomyces yeasts are becoming more widely used in oenological practice for their ability to confer wine a more complex satisfying aroma, but their metabolism remains unknown. Our study explored the nitrogen utilisation profile of three popular non-Saccharomyces species, Torulaspora delbrueckii, Metschnikowia pulcherrima and Metschnikowia fructicola. The nitrogen source preferences to support growth and fermentation as well as the uptake order of different nitrogen sources during wine fermentation were investigated. While T. delbrueckii and S. cerevisiae strains shared the same nitrogen source preferences, Metschnikowia sp. Displayed a lower capacity to efficiently use the preferred nitrogen compounds, but were able to assimilate a wider range of amino acids. During alcoholic fermentation, the non-Saccharomyces strains consumed different nitrogen sources in a similar order as S. cerevisiae, but not as quickly. Furthermore, when all the nitrogen sources were supplied in the same amount, their assimilation order was similarly affected for both S. cerevisiae and non-Saccharomyces strains. Under this condition, the rate of nitrogen source consumption of non-Saccharomyces strains and S. cerevisiae was comparable. Overall, this study expands our understanding about the preferences and consumption rates of individual nitrogen sources by the investigated non-Saccharomyces yeasts in a wine environment. This knowledge provides useful information for a more efficient exploitation of non-Saccharomyces strains that improves the management of the wine fermentation.

Specific Phenotypic Traits of Starmerella bacillaris Related to Nitrogen Source Consumption and Central Carbon Metabolite Production during Wine Fermentation.

Over the last few years, the potential of non-Saccharomyces yeasts to improve the sensory quality of wine has been well recognized. In particular, the use of Starmerella bacillaris in mixed fermentations with Saccharomyces cerevisiae was reported as an appropriate way to enhance glycerol formation and reduce ethanol production. However, during sequential fermentation, many factors, such as the inoculation timing, strain combination, and physical and biochemical interactions, can affect yeast growth, the fermentation process, and/or metabolite synthesis. Among them, the availability of yeast-assimilable nitrogen (YAN), due to its role in the control of growth and fermentation, has been identified as a key parameter. Consequently, a comprehensive understanding of the metabolic specificities and the nitrogen requirements would be valuable to better exploit the potential of Starm. bacillaris during wine fermentation. In this study, marked differences in the consumption of the total and individual nitrogen sources were registered between the two species, while the two Starm. bacillaris strains generally behaved uniformly. Starm. bacillaris strains are differentiated by their preferential uptake of ammonium compared with amino acids that are poorly assimilated or even produced (alanine). Otherwise, the non-Saccharomyces yeast exhibits low activity through the acetaldehyde pathway, which triggers an important redistribution of fluxes through the central carbon metabolic network. In particular, the formation of metabolites deriving from the two glycolytic intermediates glyceraldehyde-3-phosphate and pyruvate is substantially increased during fermentations by Starm. bacillaris This knowledge will be useful to better control the fermentation process in mixed fermentation with Starm. bacillaris and S. cerevisiaeIMPORTANCE Mixed fermentations using a controlled inoculation of Starmerella bacillaris and Saccharomyces cerevisiae starter cultures represent a feasible way to modulate wine composition that takes advantage of both the phenotypic specificities of the non-Saccharomyces strain and the ability of S. cerevisiae to complete wine fermentation. However, according to the composition of grape juices, the consumption by Starm. bacillaris of nutrients, in particular of nitrogen sources, during the first stages of the process may result in depletions that further limit the growth of S. cerevisiae and lead to stuck or sluggish fermentations. Consequently, understanding the preferences of non-Saccharomyces yeasts for the nitrogen sources available in grape must together with their phenotypic specificities is essential for an efficient implementation of sequential wine fermentations with Starm. bacillaris and S. cerevisiae species. The results of our study demonstrate a clear preference for ammonium compared to amino acids for the non-Saccharomyces species. This finding underlines the importance of nitrogen sources, which modulate the functional characteristics of inoculated yeast strains to better control the fermentation process and product quality.

Key role of lipid management in nitrogen and aroma metabolism in an evolved wine yeast strain.

BackgroundFermentative aromas play a key role in the organoleptic profile of young wines. Their production depends both on yeast strain and fermentation conditions. A present-day trend in the wine industry consists in developing new strains with aromatic properties using adaptive evolution approaches. An evolved strain, Affinity™ ECA5, overproducing esters, was recently obtained. In this study, dynamics of nitrogen consumption and of the fermentative aroma synthesis of the evolved and its ancestral strains were compared and coupled with a transcriptomic analysis approach to better understand the metabolic reshaping of Affinity™ ECA5.ResultsNitrogen assimilation was different between the two strains, particularly amino acids transported by carriers regulated by nitrogen catabolite repression. We also observed differences in the kinetics of fermentative aroma production, especially in the bioconversion of higher alcohols into acetate esters. Finally, transcriptomic data showed that the enhanced bioconversion into acetate esters by the evolved strain was associated with the repression of genes involved in sterol biosynthesis rather than an enhanced expression of ATF1 and ATF2 (genes coding for the enzymes responsible for the synthesis of acetate esters from higher alcohols).ConclusionsAn integrated approach to yeast metabolism—combining transcriptomic analyses and online monitoring data—showed differences between the two strains at different levels. Differences in nitrogen source consumption were observed suggesting modifications of NCR in the evolved strain. Moreover, the evolved strain showed a different way of managing the lipid source, which notably affected the production of acetate esters, likely because of a greater availability of acetyl-CoA for the evolved strain.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0434-6) contains supplementary material, which is available to authorized users.

Sequential Use of Nitrogen Compounds by Saccharomyces cerevisiae during Wine Fermentation: a Model Based on Kinetic and Regulation Characteristics of Nitrogen Permeases

The efficiency of nitrogen use is a key determinant of the completion of alcoholic fermentation. We analyzed the kinetics of consumption of 18 nitrogen compounds by 14 Saccharomyces cerevisiae strains of various origins in a synthetic medium that mimicked a grape must. The kinetic profiles of total nitrogen consumption were diverse, but the order of nitrogen source consumption was similar for all strains. The nitrogen compounds could be classified into three groups, according to their order of use: prematurely consumed (Lys), early consumed (Asp, Thr, Glu, Leu, His, Met, Ile, Ser, Gln, and Phe), and late consumed (ammonium, Val, Arg, Ala, Trp, and Tyr). The initial concentrations of these compounds did not alter the order in which they were consumed, except for arginine and ammonium. Early consumed amino acids are transported by specific permeases under Ssy1p-Ptr3p-Ssy5 (SPS)-mediated control that are expressed at the beginning of consumption. Most nitrogen compounds consumed late are transported by permeases under nitrogen catabolite repression (NCR), and others (Val, Trp, and Tyr) are transported by SPS-regulated low-affinity permeases. Therefore, the kinetic characteristics of transporters, as well as SPS and NCR, are likely key factors controlling the temporal sequence of consumption of nitrogen compounds and constitute a system highly conserved in S. cerevisiae species. This work sheds new light on the mechanistic basis of the sequential use of different nitrogen compounds in complex environments.

Effects of flow field on the metabolic characteristics of Streptomyces lincolnensis in the industrial fermentation of lincomycin

In this work, the flow field in the existing fermentor with radial-flow impellers (C1) was studied using the computational fluid dynamics (CFD) software package Fluent, then the fermentor with radial-axial flow impellers (C2) was constructed and was compared with the C1 fermentor by CFD and experimental research. The simulation results revealed that the flow field in C2 fermentor had characteristics such as higher turbulent kinetic energy, gas holdup and shear rates. Metabolic variables of Streptomyces lincolnensis in the two fermentors such as carbon and nitrogen source consumption rates, specific growth rates (μ), hyphae morphologies, and lincomycin productivities were further explored. The correlation analysis between the experimental measurements and the simulation results indicated that the hyphae clustering and dry cell weight (DCW) decreasing at production stage were eliminated in C2 fermentor, which had higher gas volumetric mass transfer coefficient (K(L)a), dissolved oxygen (DO) concentration and consumption rates of nutrient materials. When C2 was employed in the fermentor, the specific growth rate of S. lincolnensis at growth stage was higher, and the maintenance metabolism together with secondary metabolism at production stage was kept at higher levels. As a result, the yield of lincomycin was achieved 7039 μg ml(-1) when the 60 m(3) industrial fermentor was equipped with C2, which was increased by 46% compared to that obtained in the C1 fermentor.

Identification of genes related to nitrogen uptake in wine strains of Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae is the main microorganism responsible for wine fermentation and its development influences the quality of wine. A problem affecting these types of fermentations, generating important losses in this industry, are the slow or stuck fermentations which may result from low nitrogen availability in the must. Therefore, several studies have been directed towards identifying genes involved in nitrogen metabolism using high throughput strategies which include subjecting the yeast to changes in the type or concentration of the available nitrogen source. However, this type of approach can also generate responses in the yeast that do not necessarily alter the expression of genes related to nitrogen metabolism. In this work, by using intraspecific hybridisation of wild wine yeast strains we obtained genetically and oenologically similar strains with differences in the consumption of nitrogen sources. Using the same must, the global expression patterns of these yeasts were compared by microarrays, the analysis of which identified 276 genes that varied in their expression between the strains analysed. The functional analysis of the genes with a known function indicates that some participate in nitrogen metabolism, alcoholic fermentation, ion transport and transcriptional regulation. Furthermore, differences were observed in the expression of genes which have been partially associated to nitrogen, as in the case of ZRT1 and ATO2. Interestingly, many of the genes identified have no known function or have not been previously associated to this phenotype.

Comparison of fermentative capacities of lactobacilli in single and mixed culture in industrial media

This paper is concerned with comparing the fermentative capacity of single and mixed cultures of lactobacilli on batch lactic acid fermentation. The fermentation characteristics of five strains of lactic acid bacteria, Lactobacillus delbrueckii subsp. lactis (ATCC 12315), Lactobacillus casei (NRRL-B1445), L. delbrueckii (NRRL-B445), Lactobacillus helveticus (NRRL-B1937), and L. casei (NRRL-B1922), were compared in de Man–Rogosa–Sharpe (MRS) media. Cell growth, glucose utilization, lactic acid synthesis, and free amino acid production were the main parameters studied. Strain B1445 was found to be the excellent lactic acid bacterium for the production of lactic acid with a high yield. Production of lactic acid from corn steep liquors by fermentation was studied using strain B1445 and mixed type of five lactobacilli. Even though nitrogen source consumption in mixed culture was lower than that of single culture, the cell density and lactic acid production were better in mixed culture than single culture. These results suggest that mixed culturing of lactobacilli may be more effective than single culturing of Lactobacillus for improving lactic acid production.

Kinetic analysis of growth and xanthan gum production with Xanthomonas campestris on sucrose, using sequentially consumed nitrogen sources.

A batch fermentation strategy using Xanthomonas campestris ATCC 13951 for xanthan gum production has been established in which all essential medium components are supplied at the onset. This has been achieved using sucrose as sole sugar feedstock. Sequential consumption of nitrogen sources (soybean hydrolysates, ammonium and nitrate salts) was observed to facilitate the further optimisation of the medium. Biomass accumulation was limited by phosphate availability. Xanthan yields of more than 60% (grams of xanthan per gram of sugar) have been obtained with constant acetyl content. However, pyruvyl substitution decreased as the growth rate declined, due to the metabolic constraints specific to phosphate depletion. High rates of carbon conversion into xanthan were observed throughout the culture and the ATP/ADP ratio was not affected by the decline in the specific growth rate.

Bacteriocin production with Lactobacillus amylovorus DCE 471 is improved and stabilized by fed-batch fermentation.

Amylovorin L471 is a small, heat-stable, and hydrophobic bacteriocin produced by Lactobacillus amylovorus DCE 471. The nutritional requirements for amylovorin L471 production were studied with fed-batch fermentations. A twofold increase in bacteriocin titer was obtained when substrate addition was controlled by the acidification rate of the culture, compared with the titers reached with constant substrate addition or pH-controlled batch cultures carried out under the same conditions. An interesting feature of fed-batch cultures observed under certain culture conditions (constant feed rate) is the apparent stabilization of bacteriocin activity after obtaining maximum production. Finally, a mathematical model was set up to simulate cell growth, glucose and complex nitrogen source consumption, and lactic acid and bacteriocin production kinetics. The model showed that bacterial growth was dependent on both the energy and the complex nitrogen source. Bacteriocin production was growth associated, with a simultaneous bacteriocin adsorption on the producer cells dependent on the lactic acid accumulated and hence the viability of the cells. Both bacteriocin production and adsorption were inhibited by high concentrations of the complex nitrogen source.

Effect of external pH on yield, morphology and cell components ofCandida utilis growing in continuous culture

The physiological state ofCandida utilis growing in continuous culture was controlled by external pH and dilution rate. The pH of the medium influences the physiological mechanisms coupled with the maintenance of living functions. The consumption of nitrogen source for biomass formation is a linear function of growth rate, independent of external pH. The statistical distribution of cell volumes was identified as log-normal where the dispersion is indirectly proportional to the maintenance coefficient and the mean of the logarithm of cell volume is a linear combination of specific growth rate and maintenance coefficient. The content of RNA, protein, glucan and mannan in dry biomass may also be expressed as a simple function of specific growth rate and maintenance coefficient.

State Identification and Control Strategy in Penicillin Fermentation

The most existing industrial fermentation processes of antibiotics are controlled manually and empirically, which results in relatively low and fluctuated fermentation levels. For increasing the fermentation level, on-line optimal computer control is a very important technique. In this work a new technique based on process modelling and computer control has been developed for industrial penicillin fermentation. As a basis of computer control three models should be established beforehand monitor model - to relate the on - line measurable variables to the biological process variables; kinetic model - to decide the consumption rate of nutrient components and the formation rates of biomass and secondary metabolite product; and control model - to determine the control variables. A lab-scale computer coupled fermentation system (5L) was developed, which can on-line monitor pH, dissolved oxygen level (D. O), temperature, aeration rate, agitation speed, antifoam, pressure, concentrations of oxygen and carbon dioxide in effluent, and can calculate up to 12 variables in real time, including the carbon dioxide production rate [CPR], oxygen uptake rate (OUR), respiratory quotient (R.Q), oxygen transfer coefficient (ka) etc. A feeding device was controlled by this computer system, which can control the feed-rates of sugar, nitrogen source and precursor according to a built-in model. This system has been employed to simulate an industrial penicillin fermentation process. Through investigation of the time courses it was found that the variation of carbondioxide production rate with time has a close relation to the fermentation states, which are characterized as fast growing phase, transient phase and production phase. Referring to the variation of pH, the fermentation stages can be determined from the changing rate of [CPR]. During the production phase the level of sugar should be controlled strictly. It was first found that there exists a proportional relation between the total amount of sugar consumed and the total amount of carbondioxide released, the slope of the regression line being 1.55 g sugar/n-L CO2. Consequently, the feeding rate of sugar can be estimated by the on-line measured carbon dioxide production rate. A pseudohomogeneous kinetic model was set up. The relation among sugar consumption rate, nitrogen source consumption rate and product accumulation rate was described by this model. The feeding rates of sugar, nitrogen source and precursor in different fermentation stages can thus be resolved. By this technique based on the above models the fermentation level was increased from 30,000 u/mL to 38,000 u/mL in lab-scale study, the best result was 45,200 u/mL. In a pharmaceutical factory a two stage computer system was set up, controlled by the same model, the fermentation level in a 100 M3 fermentor was increased by 25%.