Enhancement of erythromycin A production with feeding available nitrogen sources in erythromycin biosynthesis phase

Effects of feeding different available nitrogen sources from 80 h in erythromycin biosynthesis phase on the erythromycin A (Er-A) production were investigated in 50 l fermenter. Feeding corn steep liquor and yeast extract, the Er-A production was enhanced, while the biotransformation from erythromycin C (Er-C) to Er-A had no increase. When ammonium sulphate was fed at high feeding rate, the maximal Er-A production and ratio of Er-A to Er-C were 7953 U/ml and 98.18:1 at 184 h, respectively, which were higher than that of the control (6742 U/ml and 5.47:1). The feeding ammonium sulphate process was successfully scaled up from 50 l to 25 m³ fermenter. The maximal Er-A production reached 7938 U/ml at 203 h, which was enhanced by 22.1% compared with the control (6501 U/ml at 192 h). The ratio of Er-A to Er-C was 24.05:1, which was higher than that of the control (4.77:1).     

Biochemical parameters of Saccharopolyspora Erythraea during feeding ammonium sulphate in erythromycin biosynthesis phase

The physiology of feeding ammonium sulphate in erythromycin biosynthesis phase of Saccharopolyspora erythraea on the regulation of erythromycin A (Er-A) biosynthesis was investigated in 50 L fermenter. At an optimal feeding ammonium sulphate rate of 0.03 g/L per h, the maximal Er-A production was 8281 U/mL at 174 h of growth, which was increased by 26.3% in comparison with the control (6557 U/mL at 173 h). Changes in cell metabolic response of actinomycete were observed, i.e. there was a drastic increase in the level of carbon dioxide evolution rate and oxygen consumption. Assays of the key enzyme activities and organic acids of S. erythraea and amino acids in culture broth revealed that cell metabolism was enhanced by ammonium assimilation, which might depend on the glutamate transamination pathway. The enhancement of cell metabolism induced an increase of the pool of TCA cycle and the metabolic flux of erythromycin biosynthesis. In general, ammonium assimilation in the erythromycin biosynthesis phase of S. erythraea exerted a significant impact on the carbon metabolism and formation of precursors of the process for dramatic regulation of secondary metabolites biosynthesis.     

Oxygen uptake rate optimization with nitrogen regulation for erythromycin production and scale-up from 50 L to 372 m3 scale

Effects of different nitrogen sources on the erythromycin production were investigated in 50 l fermenter with multi-parameter monitoring system firstly. With the increase of soybean flour concentration from 27 g/l to 37 g/l to the culture medium, the erythromycin production had no obvious increase. Whereas adding corn steep liquor 15 g/l in the medium was beneficial for the production of erythromycin, the maximum erythromycin production was 22.2% higher than that of the control. It was found that corn steep liquor can regulate and enhance the oxygen uptake rate (OUR) which characterizes the activity of the microbial metabolism by inter-scale observation and data association. Both Intracellular and extracellular organic acids of central metabolism were analyzed, and it was found that the whole levels of lactic acid, pyruvic acid, citric acid, and propionic acid were higher than those of control before 64th h. The consumption amount of amino acids, which could be transformed into the precursors for erythromycin synthesis (i.e. threonine, serine, alanine, glycine and phenylalanine), were elevated compared with the control in erythromycin biosynthesis phase. The results indicated that corn steep liquor can regulate OUR to certain level in the early phase of fermentation, and enhance the metabolic flux of erythromycin biosynthesis. Erythromycin production was successfully scaled up from a laboratory scale (50 l fermenter) to an industrial scale (132 m(3) and 372 m(3)) using OUR as the scale-up parameter. Erythromycin production on industrial scale was similar to that at laboratory scale.     

Kinetics and modelling of kojic acid production by Aspergillus flavus Link in batch fermentation and resuspended mycelial system

An unstructured model based on logistic and Luedeking-Piret equations was proposed to describe growth, substrate consumption and kojic acid production by Aspergillus flavus Link strain 44-1 in batch fermentation and also in a resuspended cell system. The model showed that kojic acid production was non-growth associated. The maximum kojic acid and cell concentrations obtained in batch fermentations using the fermenter with optimized dissolved oxygen control (32.5 g/l and 11.8 g/l, respectively) and using a shake-flask (36.5 and 12.3 g/l, respectively) were not significantly different. However, the maximum specific growth rate and a non-growth-associated rate constant for kojic acid formation (n) for batch fermentation using the fermenter (0.085/h and 0.0125 g kojic acid/g cell.h, respectively) were approximately three and two times higher than the values obtained for fermentation using a shake-flask, respectively. Efficient conversion of glucose to kojic acid was achieved in a resuspended pellet or mycelial system, in a solution containing only glucose with citrate buffer at pH 3.5 and at a temperature of 30 °C. The resuspended cell material in the glucose solution was still active in synthesizing kojic acid after prolonged incubation (up to about 600 h). The rate constant of kojic acid production (n) in a resuspended cell system using 100 g glucose/l was almost constant at an average value of 0.011 g kojic acid/g cell.h up to a cell concentration of 19.2 g/l, above which it decreased. A drastic reduction of n was observed at a cell concentration of 26.1 g/l. However, the yield based on glucose consumed (0.45 g/g) was similar for all cell concentrations investigated.     

Real-time fluid dynamics investigation and physiological response for erythromycin fermentation scale-up from 50 L to 132 m<Superscript>3</Superscript> fermenter

The physiological response of erythromycin fermentation scale-up from 50 L to 132 m³ scale was investigated. A relatively high oxygen uptake rate (OUR) in early phase of fermentation was beneficial for erythromycin biosynthesis. Correspondingly, the maximal consistency coefficient (K) reflecting non-Newtonian fluid characteristics in 50 L and 132 m³ fermenter also appeared in same phase. Fluid dynamics in different scale bioreactor was further investigated by real-time computational fluid dynamics modeling. The results of simulation showed that the impeller combination in 50 L fermenter could provide more modest flow field environment compared with that in 132 m³ fermenter. The decrease of oxygen transfer rate (OTR) in 132 m³ fermenter was the main cause for impairing cell physiological metabolism and erythromycin biosynthesis. These results were helpful for understanding the relationship between hydrodynamic environment and physiological response of cells in bioreactor during the scale-up of fermentation process.     

Extractive bioconversion of 2-phenylethanol from L-phenylalanine by Saccharomyces cerevisiae

The bioconversion of L-phenylalanine (L-Phe) to 2-phenylethanol (PEA) by the yeast Saccharomyces cerevisiae is limited by the toxicity of the product. PEA extraction by a separate organic phase in the fermenter is the ideal in situ product recovery (ISPR) technique to enhance productivity. Oleic acid was chosen as organic phase for two-phase fed-batch cultures, although it interfered to some extent with yeast viability. There was a synergistic inhibitory impact toward S. cerevisiae in the presence of PEA, and therefore a maximal PEA concentration in the aqueous phase of only 2.1 g/L was achieved, compared to 3.8 g/L for a normal fed-batch culture. However, the overall PEA concentration in the fermenter was increased to 12.6 g/L, because the PEA concentration in the oleic phase attained a value of 24 g/L. Thus, an average volumetric PEA production rate of 0.26 g L(-1) h(-1) and a maximal volumetric PEA production rate of 0.47 g L(-1) h(-1) were achieved in the two-phase fed-batch culture. As ethanol inhibition had to be avoided, the production rates were limited by the intrinsic oxidative capacity of S. cerevisiae. In addition, the high viscosity of the two-phase system lowered the k(l)a, and therefore also the productivity. Thus, if a specific ISPR technique is planned, it consequently has to be remembered that the productivity of this bioconversion process is also quickly limited by the k(l)a of the fermenter at high cell densities.     

Application of oxygen uptake rate and response surface methodology for erythromycin production by Saccharopolyspora erythraea

A process for efficient production of erythromycin by Saccharopolyspora erythraea using statistical designs and feeding strategy was developed. The critical nutrient components were selected in accordance with fractional factorial design and were further optimized via response surface methodology. Three significant components (ZnSO₄, citric acid threonine) were identified for the optimization study. The optimum levels of these significant variables were determined with Box–Behnken design, which were ZnSO₄ 0.039 g/l, citric acid 0.24 g/l and threonine 0.42 g/l, respectively. A novel feeding strategy based on oxygen uptake rate (OUR) measurement was developed successfully to increase the flux of erythromycin biosynthesis, in which the optimized nutrient components was fed in the 50 l stirred bioreactor when OUR began to decline at 46 h. The maximum erythromycin production reached 10,622 U/ml, which was 11.7% higher than the control in the same cultivation conditions. It was the first report to integrate physiological parameter OUR and statistical methods to optimize erythromycin production.     

Kinetics of cell growth and cyclosporin A production by Tolypocladium inflatum when scaling up from shake flask to bioreactor

The kinetics of cell growth and Cyclosporin A (Cyc A) production by Tolypocladium inflatum were studied in shake flasks and bioreactors under controlled and uncontrolled pH conditions. In the case of the shake flask, the production time was extended to 226 h and the maximal antibiotic concentration was 76 mg/l. When scaling up the cultivation process to a bioreactor level, the production time was reduced to only 70 h with a significant increase in both the cell growth and the antibiotic production. The maximal dry cell weights in the case of the controlled pH and uncontrolled pH cultures in the bioreactor were 22.4 g/l and 14.2 g/l, respectively. The corresponding maximal dry cell weight values did not exceed 7.25 g/l with the shake flask cultures. The maximal values for Cyc A production were 144.72 and 131.4 mg/l for the controlled and uncontrolled pH cultures, respectively. It is also worth noting that a significant reduction was observed in both the dry cell mass and the antibiotic concentration after the Cyc A production phase, whereas the highest rate of antibiotic degradation was observed in the stirred tank bioreactor with an uncontrolled pH. Morphological characterization of the micromorphological cell growth (mycelial/pellet forms) was also performed during cultivation in the bioreactor.     

Improved poly-ε-lysine biosynthesis using Streptomyces noursei NRRL 5126 by controlling dissolved oxygen during fermentation

The growth kinetics of Streptomyces noursei NRRL 5126 was investigated under different aeration and agitation combinations in a 5.0 l stirred tank fermenter. Poly-epsilon-lysine biosynthesis, cell mass formation, and glycerol utilization rates were affected markedly by both aeration and agitation. An agitation speed of 300 rpm and aeration rate at 2.0 vvm supported better yields of 1,622.81 mg/l with highest specific productivity of 15 mg/l.h. Fermentation kinetics performed under different aeration and agitation conditions showed poly- epsilon-lysine fermentation to be a growth-associated production. A constant DO at 40% in the growth phase and 20% in the production phase increased the poly-epsilon-lysine yield as well as cell mass to their maximum values of 1,992.35 mg/l and 20.73 g/l, respectively. The oxygen transfer rate (OTR), oxygen utilization rate (OUR), and specific oxygen uptake rates (qO2) in the fermentation broth increased in the growth phase and remained unchanged in the stationary phase.     

Production of heterologous protein by Methylobacterium extorquens in high cell density fermentation

The green fluorescent protein (GFP) was used as a model protein to study the recombinant protein production by the strain Methylobacterium extorquens ATCC 55366. Scale-up from shake flasks to 20 l fed-batch fermentation was achieved using methanol as a sole carbon and energy source and a completely minimal culture medium. Two different expression vectors were used to express GFP. Clone PCM-GFP containing the vector pCM110 with native promoter of the methanol dehydrogenase PmxaF produced approximately 100-fold more GFP than the clone PRK-GFP containing the vector pRK310 with the heterogeneous promoter Plac. Several fed-batch fermentations with and without selective pressure (tetracycline) were run in a 20 l stirred tank fermenter using the two different clones of M. extorquens. The methanol concentration was monitored with an on-line semiconductor gas sensor in the culture broth. It was maintained at a non-toxic level of 1.4 g l(-1) with an adaptative control which regulates the methanol feed rate. The same growth profile was achieved in all fermentations. The maximum growth rate (micro(max)) was 0.18 h(-1) with an overall yield (Y(X/S)) of 0.3 g g(-1) methanol. With this high cell density fermentation process, we obtained high levels (up to 4 g l(-1)) of GFP with the clone PCM-GFP. The maximum specific GFP production (Y(GFP/X)) with this clone was 80 mg g(-1) representing approximately 16% of the total cell protein. Additional feeding of pure oxygen to the fermenter permitted a longer phase of exponential growth but had no effect on the total yields of biomass and GFP. The specific GFP production of clone PCM-GFP remained unaffected in the presence or absence of selective pressure (tetracycline), within the initial 50 h of the fermentation culture. These results suggest that M. extorquens ATCC 55366 could be an interesting candidate for overexpression of recombinant proteins.     

Controlling the feed rate of propanol to optimize erythromycin fermentation by on-line capacitance and oxygen uptake rate measurement

The aim of the present study was to optimize the feeding proportion of glucose and propanol for erythromycin biosynthesis by real-time monitoring and exploring its limited ratio by the on-line multi-frequency permittivity measurement. It was found that the capacitance values were sensitive to the variation of biomass concentration and microbial morphology as well as the true state of cell growth. It was most favorable to both cell growth and secondary metabolism to keep the ratio of glucose to propanol at 4.3 (g/g). The specific growth rate calculated by the capacitance measurement correctly and accurately reflected the cell physiological state. An appropriate feed rate of propanol was crucial for cell growth and secondary metabolism, as well as to improve the quality of erythromycin-A. In addition, the erythromycin production titer (10,950 U/mL) was further enhanced by 4 % when the propanol feed was regulated by step-down strategy based on both OUR (oxygen uptake rate) and the on-line monitoring capacitance.     

Production of carbonyl reductase by Geotrichum candidum in a laboratory scale bioreactor

Fungal fermentation is very complex in nature due to its nonlinear relationship with the time, especially in batch culture. Growth and production of carbonyl reductase by Geotrichum candidum NCIM 980 have been studied in a laboratory scale stirred tank bioreactor at different pH (uncontrolled and controlled), agitation, aeration and dissolved oxygen concentration. The yield of the process has been calculated in terms of glucose consumed. Initial studies showed that fermenter grown cells have more than 15 times higher activity than that of the shake flask grown cells. The medium pH was found to have unspecific but significant influence on the enzyme productivity. However, at controlled pH 5.5 the specific enzyme activity was highest (306U/mg). Higher agitation had detrimental effect on the cell mass production. Dissolved oxygen concentration was maintained by automatic control of the agitation speed at an aeration rate of 0.6 volume per volume per minute (vvm). Optimization of glucose concentration yielded 21g/l cell mass with and 9.77x10(3)U carbonyl reductase activity/g glucose. Adaptation of different strategies for glucose feeding in the fermenter broth was helpful in increasing the process yield. Feeding of glucose at a continuous rate after 3h of cultivation yielded 0.97g cell mass/g glucose corresponding to 29.1g/l cell mass. Volumetric oxygen transfer coefficient (K(L)a) increased with the increasing of agitation rate.     

Statistical optimization of the medium composition by response surface methodology to enhance schizophyllan production by Schizophyllum commune

The response surface methodology (RSM) involving central composite design (CCD) was employed to optimize the fermentation medium for the cell growth and schizophllan production by Schizophyllum commune CGMCC 5.113 in submerged culture at pH 6.5 and 26 degrees C. The four variables involved in this study were glucose, yeast extract, ammonium nitrate, and magnesium sulfate. The statistical analysis of the results showed that, in the range studied, glucose and yeast extract had a highly significant effect on schizophyllan production. The optimal medium for schizophyllan production calculated from the regression model of RSM was as follows: glucose, 18 g/l; yeast extract, 0.5 g/l; NH4NO3, 0.48 g/l; and MgSO4, 0.05 g/l, with a predicted maximum schizophyllan production of 11.74 g/l. These predicted values were experimentally validated. The excellent correlation between predicted and measured values justifies the validity of the response model. The results of bioreactor fermentation also show that the optimized medium enhanced schizophyllan production (12.80 g/l) by S. commune in a 5-1 fermenter.     

Cell reuse in submerged lactic acid batch fermentation

The reusability of biomass in lactic acid batch fermentation with free cells of Lactobacillus paracasei was studied in a 2–1 fermenter and in a 50-1 fermenter. In lab-scale fermentation experiments, 33 to 100% of the cell mass formed was reused in the subsequent batch in each case. In a series of seven consecutive batches, maximum values of lactate formation productivity of 6.32 to 11.54 g/l × h were observed at initial cell concentrations of 2.1 to 24.6 g/l. In all of the experiments, the initial cell viability was 78% or greater than 78%, and the final cell viability did not fall below 70%. At cell concentrations above 20 g/l, the productivity of lactic acid formation did not increase further, but remained constant. Because its level could be influenced by varying the proportions between the content of yeast extract, peptone and initial cell mass (1:1:2, 1:1:1 and 3.3.1) in the medium and no inhibitory effects were observed, this finding can be attributed to nutrient limitation. A low degree of cell reuse was reached in an analogous series of experiments carried out in a 50-1 fermenter. In this case, the initial cell concentration varied between 0.5 and 1.1 g/l, and therefore cell growth was not limited by nutrients in the first period of fermentation. Lactate production was still stable after six cell-reuse operations. The lactic acid yield did not fall below 90%. Temporary storage of the biomass in a refrigerator for a time interval of one to two weeks caused no significant impairment of overall lactate production, but a proportional prolongation of the lag phase occurred with increasing duration of storage.     

Isomaltulose production using free cells: optimisation of a culture medium containing agricultural wastes and conversion in repeated-batch processes

The enzyme glucosyltransferase is an industrially important enzyme since it produces non-cariogenic isomaltulose (6-O-alpha-D-glucopyronosyl-1-6-D-fructofuranose) from sucrose by intramolecular transglucosylation. The experimental designs and response surface methodology (RSM) were applied for the optimisation of the nutrient concentrations in the culture medium for the production of glucosyltransferase by Erwinia sp. D12 in shaken flasks at 200 rpm and 30 degrees C. A statistical analysis of the results showed that, in the range studied, the factors had a significant effect (P < 0.05) on glucosyltransferase production and the highest enzyme activity (10.84 U/ml) was observed in culture medium containing sugar cane molasses (150 g l(-1)), corn steep liquor (20 g l(-1)), yeast extract Prodex Lac SD (15 g l(-1)) and K2HPO4 (0.5 g l(-1)) after 8 h at 30 degrees C. The production of cell biomass by the strain of Erwinia sp. D12 was carried out in a 6.6-l fermenter with a mixing rate of 200 rpm and an aeration rate of 1 vvm. Fermentation time, cellular growth, medium pH and glucosyltransferase production were observed. The greatest glucosyltransferase activity was 22.49 U/ml, obtained after 8 h of fermentation. The isomaltulose production from sucrose was performed using free Erwinia sp. D12 cells in a batch process using an orbital shaker. The influence of the parameters sucrose concentration, temperature, pH, and cell concentration on the conversion of sucrose into isomaltulose was studied. The free cells showed a high conversion rate of sucrose into isomaltulose using batch fermentation, obtaining an isomaltulose yield of 72.11% from sucrose solution 35% at 35 degrees C.     

Extracellular 5-aminolevulinic acid production by Escherichia coli containing the Rhodopseudomonas palustris KUGB306 hemA gene

The Rhodopseudomonas palustris KUGB306 hemA gene codes for 5-aminolevulinic acid (ALA) synthase. This enzyme catalyzes the condensation of glycine and succinyl-CoA to yield ALA in the presence of the cofactor pyridoxal 5'- phosphate. The R. palustris KUGB306 hemA gene in the pGEX-KG vector system was transformed into Escherichia coli BL21. The effects of physiological factors on the extracellular production of ALA by the recombinant E. coli were studied. Terrific Broth (TB) medium resulted in significantly higher cell growth and ALA production than did Luria-Bertani (LB) medium. ALA production was significantly enhanced by the addition of succinate together with glycine in the medium. Maximal ALA production (2.5 g/l) was observed upon the addition of D-glucose as an ALA dehydratase inhibitor in the late-log culture phase. Based on the results obtained from the shake-flask cultures, fermentation was carried out using the recombinant E. coli in TB medium, with the initial addition of 90 mM glycine and 120 mM succinate, and the addition of 45 mM D-glucose in the late-log phase. The extracellular production of ALA was also influenced by the pH of the culture broth. We maintained a pH of 6.5 in the fermenter throughout the culture process, achieving the maximal levels of extracellular ALA production (5.15 g/l, 39.3 mM).     

Optimization of the medium composition for production of mycelial biomass and exo-polymer by Grifola frondosa GF9801 using response surface methodology

In this work, a three-level Box-Behnken factorial design was employed combining with response surface methodology (RSM) to optimize the medium composition for the production of the mycelial biomass and exo-polymer in submerged cultures by Grifola frondosa GF9801. A mathematical model was then developed to show the effect of each medium composition and their interactions on the production of mycelial biomass and exo-polymer. The model estimated that, a maximal yield of mycelial biomass (17.61 g/l) could be obtained when the concentrations of glucose, KH2PO4, peptone were set at 45.2 g/l, 2.97 g/l, 6.58 g/l, respectively; while a maximal exo-polymer yield (1.326 g/l) could be achieved when setting concentrations of glucose, KH2PO4, peptone at 58.6 g/l, 4.06 g/l and 3.79 g/l, respectively. These predicted values were also verified by validation experiments. Compared with the values obtained by other runs in the experimental design, the optimized medium resulted in a significant increase in the yields of mycelial biomass and exo-polymer. Maximum mycelial biomass yield of 22.50 g/l was achieved in a 15-l fermenter using the optimized medium.     

Proline-based modulation of 2,4-diacetylphloroglucinol and viable cell yields in cultures of Pseudomonas fluorescens wild-type and over-producing strains

The antifungal compound 2,4-diacetylphloroglucinol (DAPG) is produced in the rhizosphere of wheat by pseudomonad populations responsible for the natural biological control phenomenon known as “take-all decline.” Studies were conducted to elucidate the impact of DAPG and its co-product 2,4,6-trihydroxyacetophenone (THA) on the production of Pseudomonas fluorescens for biological control. Increasing DAPG from 0.1 g/l to 0.5 g/l and THA from 0.05 g/l to 0.5 g/l significantly inhibited the growth and lowered the yield of viable bacteria in liquid cultures. On further examination of these metabolites applied in seed coatings, levels of DAPG and THA exceeding 0.05 mg/g seed significantly reduced wheat germination percentages. The three-way interaction of DAPG, THA, and culture medium ingredients was significant, and greatest seed germination loss (40–50%) was observed when 0.5 mg DAPG and 0.25 mg THA were combined in a coating of 0.5 ml culture medium per gram of seed. Based on the results of Biolog GN microplate, flask, and fermentor screens of C sources, proline was found to optimize the viable cell yields of the P. fluorescens strains tested. The combination of proline with glucose and urea as C and N sources in growth media could be optimized to minimize DAPG production and maximize the vitality of P. fluorescens Q8R1-96 and Q69c-80:miniTn5:phl20 (DAPG over-producer). In production cultures, the proline supply rate offers a potentially useful means to optimize the biological control agent yield and quality.     

Improved arachidonic acids production from the fungus Mortierella alpina by glutamate supplementation

The effect of various concentrations of glutamate on arachidonic acid (AA) production from Mortierella alpina in shaker flask culture was studied. Glutamate supplementation promoted Mortierella growth, accelerated substrate metabolism, and increased AA production, and a concentration of 0.8 g/l glutamate resulted in the greatest AA yield (1.41 g/l). In 10 l airlift stirred fermenter culture, AA yield in the cultures exposed to 0.8 g/l glutamate was also greater than that in the control (0.56 g/l).     

Optimization of lipid production in the oleaginous yeastApiotrichum curvatum in wheypermeate

Summary Lipid production of the oleaginous yeastApiotrichum curvatum was studied in wheypermeate to determine optimum operation conditions in this medium. Studies on the influence of the carbon to nitrogen ratio (C/N-ratio) of the growth medium on lipid production in continuous cultures demonstrated that cellular lipid content in wheypermeate remained constant at 22% of the cell dry weight up to a C/N-ratio of about 25. The maximal dilution rate at which all lactose is consumed in wheypermeate with excess nitrogen was found to be 0.073 h^-1. At C/N-ratios higher than 25–30 lipid content gradually increased to nearly 50% at C/N=70 and the maximal obtainable dilution rate decreased to 0.02 h^-1 at C/N=70. From these studies it could be derived that maximal lipid production rates can be obtained at C/N-ratios of 30–35 in wheypermeate. Since the C/N-ratio of wheypermeate normally has a value between 70 and 101, some additional nitrogen is required to optimize the lipid production rate. Lipid production rates ofA. curvatum in wheypermeate were compared in four different culture modes: batch, fed-batch, continuous and partial recycling cultures. Highest lipid production rates were achieved in culture modes with high cell densities. A lipid production rate of nearly 1 g/l/h was reached in a partial recycling culture. It was calculated that by using this cultivation technique lipid production rates of even 2.9 g/l/h may be reached when the supply of oxygen can be optimized.Nomenclature C/N-ratio carbon to nitrogen ratio of the growth medium (g/g) - C/N_crit C/N-ratio at which there is just enough nitrogen to allow all carbon source to be converted to biomass - D dilution rate=volume of incoming medium per unit time/volume of medium in the culture vessel (h^-1) - D_max maximum dilution rate (h^-1) - DW cell dry weight - L lipid yield (g storage lipid/g carbon source) - specific growth rate (h^-1) - _max maximum specific growth rate (h^-1) - Q_L lipid production rate (g/l/h) - Y_i molecular fraction of carbon substrate that is converted to storage carbohydrate (C-mol/C-mol) - Y_ls maximal amount of storage lipid that can be produced per mol carbon source (C-mol/C-mol)