Stirred Tank Fermentor Research Articles

10.2478/s11814-009-0179-6

The effect of medium components and environmental factors on the production of mycelial biomass for the preparation of intracellular polysaccharides (IPS) and exopolysaccharides (EPS) by Cordyceps takaomontan was investigated in submerged cultures. The optimal culture condition was as follows (g/l): glucose 30, yeast extract 4, KH2PO4 0.46, K2HPO4 1, and MgSO4 0.5, and 28 °C and pH 8. When the fungus was cultivated under various agitation and aeration conditions in a 5-l stirred-tank fermenter, the maximum mycelial biomass (10.7 g/l) and EPS production (1.9 g/l) was obtained at 300 rpm and 2 vvm, respectively. The inhibitory effect of both IPS and EPS on the growth of SK-N-SH cells was studied by treating the cells with crude IPS and EPS at concentrations of 0.5, 1, and 2 mg/ml for 24, 48, 72 h, respectively. The maximum inhibitory effect on apoptosis of SK-N-SH cells (64.6%) was observed when IPS was treated at a concentration of 2 mg/ml, for 72 h. The apoptosis of SK-N-SH cells induced by IPS was evidenced by comet assay, where the number of the comet cells increased by the IPS treated. These findings suggest that IPS may therefore have therapeutic potential against neuroblastoma cells.

Production, purification and tumor necrosis factor-α (TNF-α) release capability of exopolysaccharide from Laetiporus sulphureus (Bulliard: Fries) Bondartsev & Singer in submerged cultures

The optimal culture conditions of exopolysaccharide (EPS) productions in submerged culture by Laetiporus sulphureus were determined in flask cultures. Optimal medium composition was determined as follows (g/l): glucose 10, yeast extract 5, KH2PO4 3. The optimal temperature and initial pH for EPS production were 31°C and initial pH 4.0, respectively. The optimal culture medium was then cultivated in a 5-l and a 20-l stirred tank fermenter at 1vvm (volume of aeration per volume of bioreactor per min) aeration rate, 150rpm agitation speed, controlled pH 4.0 and 31°C. In the optimal culture medium, the maximum EPS production in a 5-l and a 20-l stirred tank fermenter was 367 and 356mg/l, respectively, resulting in a 57% and 51% enhancement of EPS fermentation production compared with those from the basal medium cultures. Two main fractions, Fr-I and Fr-II, of crude EPS extracted from optimal L. sulphureus culture were obtained by a Sepharose CL-4B column chromatography. The high-performance gel-permeation chromatography (HPGPC) analysis exhibited that the number average molecular weight (Mn) of two polysaccharides were 4290 and 1120kDa, respectively. The protein contents of two fractions were 36.98% and 12.31% (w/w), respectively. All polysaccharide fractions showed significantly higher tumour necrosis factor-α (TNF-α) release capability on macrophage cells. The results obtained are useful in optimization of L. sulphureus culture for efficient production of a potent immunostimulating EPS in the submerged culture.

Production, characteristics and applications of the cell-bound phytase of Pichia anomala

Among several yeasts isolated from dried flowers of Woodfordia fruticosa, Pichia anomala produced a high titre of cell-bound phytase. The optimization of fermentation variables led to formulation of media and selection of cultural variables that supported enhanced phytase production. The enzyme productivity was very high in fed batch fermentation in air-lift fermentor as compared to that in stirred tank fermentor. Amelioration in the cell-bound phytase activity was observed when yeast cells were permeabilized with Triton-X-100. The enzyme is thermostable and acid stable with broad substrate specificity, the characteristics that are desirable for enzymes to be used in the animal feed industry. The phytase-encoding gene was cloned and sequenced. The 3D structure of the enzyme was proposed by comparative modeling using phytase of Debaryomyces occidentalis (50% sequence identity) as template. When broiler chicks, and fresh water and marine fishes were fed with the feed supplemented with yeast biomass containing phytase, improvement in growth and phosphorus retention, and decrease in the excretion of phosphorus in the faeces were recorded. The cell-bound phytase of P. anomala could effectively dephytinize wheat flour and soymilk.

Extracellular polysaccharide (EPS) production by a novel strain of yeast-like fungus Aureobasidium pullulans

A yeast-like fungus producing a large amount of extracellular polysaccharide was isolated from the biogas reactors at North Wyke Research, UK (latitude, 50°46′29″N; longitude, 3°55′23″W). This strain was identified as Aureobasidium pullulans based on nucleotide sequence of the D1/D2 domain of the large-subunit (LSU) rRNA gene. Extracellular polysaccharide or pullulan, produced from this new strain of A. pullulans in shake flasks and a stirred tank fermenter was investigated. A maximum polysaccharide concentration of 40.1 g l −1, and productivity of 12.5 g l −1 per day was obtained in a batch culture from stirred tank fermenter. The optimal cultivation conditions for pullulan production for this strain in 250 ml shake flask containing 100 ml of sucrose medium were observed at 28 °C and with 200 rpm. The effect of different sugars and nitrogen sources on pullulan production was investigated. It was found that more pullulan was produced when the strain was grown in the medium supplemented with NaNO 3 than when it was cultivated in the medium supplemented with C5 and C6 sugars and other nitrogen sources.

Scale-up from microtiter plate to laboratory fermenter: evaluation by online monitoring techniques of growth and protein expression in Escherichia coli and Hansenula polymorpha fermentations

BackgroundIn the past decade, an enormous number of new bioprocesses have evolved in the biotechnology industry. These bioprocesses have to be developed fast and at a maximum productivity. Up to now, only few microbioreactors were developed to fulfill these demands and to facilitate sample processing. One predominant reaction platform is the shaken microtiter plate (MTP), which provides high-throughput at minimal expenses in time, money and work effort. By taking advantage of this simple and efficient microbioreactor array, a new online monitoring technique for biomass and fluorescence, called BioLector, has been recently developed. The combination of high-throughput and high information content makes the BioLector a very powerful tool in bioprocess development. Nevertheless, the scalabilty of results from the micro-scale to laboratory or even larger scales is very important for short development times. Therefore, engineering parameters regarding the reactor design and its operation conditions play an important role even on a micro-scale. In order to evaluate the scale-up from a microtiter plate scale (200 μL) to a stirred tank fermenter scale (1.4 L), two standard microbial expression systems, Escherichia coli and Hansenula polymorpha, were fermented in parallel at both scales and compared with regard to the biomass and protein formation.ResultsVolumetric mass transfer coefficients (kLa) ranging from 100 to 350 1/h were obtained in 96-well microtiter plates. Even with a suboptimal mass transfer condition in the microtiter plate compared to the stirred tank fermenter (kLa = 370-600 1/h), identical growth and protein expression kinetics were attained in bacteria and yeast fermentations. The bioprocess kinetics were evaluated by optical online measurements of biomass and protein concentrations exhibiting the same fermentation times and maximum signal deviations below 10% between the scales. In the experiments, the widely applied green fluorescent protein (GFP) served as an online reporter of protein expression for both strains.ConclusionsThe successful 7000-fold scale-up from a shaken microtiter plate to a stirred tank fermenter was demonstrated in parallel fermentations for standard microbial expression systems. This confirms that the very economical and time efficient platform of microtiter plates can be very easily scaled up to larger stirred tank fermenters under defined engineering conditions. New online monitoring techniques for microtiter plates, such as the BioLector, provide even more real-time kinetic data from fermentations than ever before and at an affordable price. This paves the way for a better understanding of the bioprocess and a more rational process design.

Optimization of exopolysaccharide production fromArmillaria melleain submerged cultures

To study the optimization of submerged culture conditions for exopolysaccharide (EPS) production by Armillaria mellea in shake-flask cultures and also to evaluate the performance of an optimized culture medium in a 5-l stirred tank fermenter. Shake flask cultures for EPS optimal nutritional production contained having the following composition (in g l(-1)): glucose 40, yeast extract 3, KH(2)PO(4) 4 and MgSO(4) 2 at an optimal temperature of 22 degrees C and an initial of pH 4.0. The optimal culture medium was then cultivated in a 5-l stirred tank fermenter at 1 vvm (volume of aeration per volume of bioreactor per min) aeration rate, 150 rev min(-1) agitation speed, controlled pH 4.0 and 22 degrees C. In the optimal culture medium, the maximum EPS production in a 5-l stirred tank fermenter was 588 mg l(-1), c. twice as great as that in the basal medium. The maximum productivity for EPS (Q(p)) and product yield (Y(P/S)) were 42.02 mg l(-1) d(-1) and 26.89 mg g(-1), respectively. The optimal culture conditions we proposed in this study enhanced the EPS production of A. mellea from submerged cultures. The optimal culturing conditions we have found will be a suitable starting point for a scale-up of the fermentation process, helping to develop the production of related medicines and health foods from A. mellea.

Enhancement of Fumaric Acid Production by Rhizopus oryzae Using a Two-stage Dissolved Oxygen Control Strategy

Batch fermentative production of fumaric acid by Rhizopus oryzae ME-F12 was investigated in a 7-l stirred tank fermentor under different dissolved oxygen (DO) concentrations. High fumaric acid yield on glucose (0.56 g/g) was achieved under high DO concentration (80%), but the glucose consumption rate and fumaric acid productivity were rather low (0.91 and 0.51 g/l/h). Fumaric acid productivity was enhanced under low DO concentration (30%), but the fuamric acid yield on glucose decreased to 0.52 g/g. In order to achieve the high fumaric acid yield and productivity simultaneously, a two-stage dissolved oxygen control strategy was proposed, in which the DO concentration was controlled at 80% in the first 18 h and then switched to 30%. This was experimentally proven to be successful. Relatively high fumaric acid production (56.2 g/l), high fumaric acid yield on glucose (0.54 g/g), and high glucose consumption rate (1.3 g/l/h) were achieved by applying this strategy. The productivity (0.7 g/l/h) was improved by 37%, 21%, and 9%, respectively, compared with fermentations in which DO concentrations were kept constant at 80%, 60%, and 30%.

Enhancement of Red Pigment Production by Monascus purpureus FTC 5391 through Retrofitting of Helical Ribbon Impeller in Stirred-Tank Fermenter

The possibility of using a novel proximity type half-pitched, double-flight helical ribbon impeller (HRI) for the improvement of red pigment production by Monascus purpureus FTC5391 was investigated in a 2-L stirred-tank fermenter (STF). For comparison, the fermentations were also carried out in STF equipped with the industrial standard six-bladed Rushton turbines (RT). The selection of aeration and agitation strategies in STF were based on possible attainable oxygen transfer at the start of fermentation using derived empirical power law model to predict the initial volumetric oxygen transfer coefficient (kLa). The final pigment concentration, yield, and productivity obtained in optimized fermentation employing a single HRI agitated at 250 rpm and air flow rate of 2.25 L/min (1.5 vvm) was 24.36 UA500, 0.47 UA500/g glucose, and 0.20 UA500/h, respectively. These values were about 76%, 78%, and 96% higher than those obtained in STF fitted with RT, respectively. In terms of impeller power consumption, the HRI system was favorable for batch cultivation of M. purpureus as pigment yield per energy invested was 2.5 times higher than the RT.

Production of polysaccharides by submerged mycelial culture of entomopathogenic fungus Cordyceps takaomontana and their apoptotic effects on human neuroblastoma cells

The effect of medium components and environmental factors on the production of mycelial biomass for the preparation of intracellular polysaccharides (IPS) and exopolysaccharides (EPS) by Cordyceps takaomontan was investigated in submerged cultures. The optimal culture condition was as follows (g/l): glucose 30, yeast extract 4, KH2PO4 0.46, K2HPO4 1, and MgSO4 0.5, and 28 o C and pH 8. When the fungus was cultivated under various agitation and aeration conditions in a 5-l stirred-tank fermenter, the maximum mycelial biomass (10.7 g/l) and EPS production (1.9 g/l) was obtained at 300 rpm and 2 vvm, respectively. The inhibitory effect of both IPS and EPS on the growth of SK- N-SH cells was studied by treating the cells with crude IPS and EPS at concentrations of 0.5, 1, and 2 mg/ml for 24, 48, 72 h, respectively. The maximum inhibitory effect on apoptosis of SK-N-SH cells (64.6%) was observed when IPS was treated at a concentration of 2 mg/ml, for 72 h. The apoptosis of SK-N-SH cells induced by IPS was evidenced by comet assay, where the number of the comet cells increased by the IPS treated. These findings suggest that IPS may therefore have therapeutic potential against neuroblastoma cells.

Polygalacturonase Production by Aspergillus sp. in Air-Lift and Agitated Fermentor

Polygalacturonase production under different shear stress environments by Aspergillus sp. was studied. It was found that the rate of enzyme production in the stirred tank fermentor decreased with increasing the stirrer speed in the range 300-750 rpm. On the other hand, in a split cylinder air-lift fermentor, the rate of polygalacturonase production slightly increased with increasing in air rate from 1.5 to 2 v.v.m (volume air/culture volume/minute). The maximum enzyme titres at the end of the cultivation period in the airlift fermentor were 35 unit/ml and at least twice of that obtained in agitated fermentors. Measurement of main hyphal length in agitated and air-lift fermentors suggested break up of the mycelia in the higher shear environment of stirred fermentor especially at the higher agitation rates. The similarity in the trend of the enzyme production and main hyphal length suggested a possible relationship between the morphology and productivity of the Aspergillus sp. used in the present study.

Growth kinetics of diazotrophic Bacillus sphaericus UPMB10 cultured using different types and concentrations of carbon and nitrogen sources

Growth kinetics of newly isolated diazotrophic Bacillus sphaericus UPMB10 grown in various carbon (lactate, acetate, glycerol, malate, fructose, xylose and sucrose) and nitrogen (glutamate, yeast extract, arginine, hystadine, glycine, polypeptone, tryptophan, lysine, NH4Cl and urea) sources was investigated using 2 L stirred tank fermenter. The highest growth was obtained in a medium containing lactate as a carbon source, which gave the highest maximum cell concentration of 2.30 g/L, which is corresponding to maximum viable cell count of 4.60 x 109 cfu/mL. However, the highest cell yield (1.06 g cell/g carbon consumed) was obtained in cultivation using glycerol though slightly lower maximum viable cell count was obtained (3.22 x 109 cfu/mL). In addition, cost for the production of live cell using glycerol was about 15 times lower than the cost using lactate. Growth performance of this bacterium when yeast extract was used as a nitrogen source was comparable to the use of pure amino acid. The medium containing 1.8 g/L glycerol and 2 g/L yeast extract was suggested as optimal for growth of this bacterium, which gave carbon to nitrogen ratio (C/N) of 10:1. The maximum viable cell count obtained in cultivation using optimised medium in 2 L stirred tank fermenter was 3.34 x 109 cfu/mL and the cells maintained its capacity for N2 fixation at 18 nmol C2H2/h.mL.

Kinetic Analysis and pH-Shift Control Strategy for Propionic Acid Production with Propionibacterium Freudenreichii CCTCC M207015

The production of propionic acid by Propionibacterium freudenreichii CCTCC M207015 was investigated in a 7.5-l stirred-tank fermentor. Batch fermentations by P. freudenreichii CCTCC M207015 at various pH values ranging from 5.5 to 7.0 were studied. Based on the analysis of the time course of specific cell growth rate (mu (x)) and specific propionic acid formation rate (mu (p)), a two-stage pH-shift control strategy was proposed. At first 48 h, pH was controlled at 6.5 to obtain the maximal mu (x), subsequently pH 6.0 was used to maintain high mu (p) to enhance the production of propionic acid. By applying this pH-shift control strategy in propionic acid fermentation, the maximal propionic acid and glucose conversion efficiency had a significant improvement and reached 19.21 g/l and 48.03%, respectively, compared with those of constant pH operation (14.58 g/l and 36.45%). Fed-batch fermentation with pH-shift control strategy was also applied to produce propionic acid; the maximal propionic acid yield and glucose conversion efficiency reached 25.23 g/l and 47.76%, respectively.

Characterization and large-scale production of recombinant Streptoverticillium platensis transglutaminase

Recombinant Streptomyces platensis transglutaminase (MtgA) produced by the Streptomyces lividans transformant 25-2 was purified by ammonium sulfate fractionation, followed by CM-Sepharose CL-6B fast flow, and blue-Sepharose fast flow chromatography. The purification factor was approximately 33.2-fold, and the yield was 65%. The molecular weight of the purified recombinant MtgA was 40.0 KDa as estimated by SDS-PAGE. The optimal pH and the temperature for the enzyme activity were 6.0 and 55 degrees C, respectively, and the enzyme was stable at pH 5.0-6.0 and at temperature 45-55 degrees C. Enzyme activity was not affected by Ca(2+), Li(+), Mn(2+), Na(+), Fe(3+), K(+), Mg(2+), Al(3+), Ba(2+), Co(2+), EDTA, or IAA but was inhibited by Fe(2+), Pb(2+), Zn(2+), Cu(2+), Hg(2+), PCMB, NEM, and PMSF. Optimization of the fermentation medium resulted in a twofold increase of recombinant MtgA activity in both flasks (5.78 U/ml) and 5-l fermenters (5.39 U/ml). Large-scale productions of the recombinant MtgA in a 30-l air-lift fermenter and a 250-l stirred-tank fermenter were fulfilled with maximal activities of 5.36 and 2.54 U/ml, respectively.

Production of extracellular polysaccharides by submerged mycelial culture of Laetiporus sulphureus var. miniatus and their insulinotropic properties

In the present study, optimum culture conditions for the production of extracellular polysaccharides (EPS) in submerged culture of an edible mushroom, Laetiporus sulphureus var. miniatus and their stimulatory effects on insulinoma cell (RINm5F) proliferation and insulin secretion were investigated. The maximum mycelial growth (4.1 g l(-1)) and EPS production (0.6 g l(-1)) in submerged flask culture were achieved in a medium containing 30 g l(-1) maltose, 2 g l(-1) soy peptone, and 2 mM MnSO(4).5H2O at an initial pH 2.0 and temperature 25 degrees C. In the stirred-tank fermenter under optimized medium, the concentrations of mycelial biomass and EPS reached a maximum level of 8.1 and 3.9 g l(-1), respectively. Interestingly, supplementation of deep sea water (DSW) into the culture medium significantly increased both mycelial biomass and EPS production by 4- and 6.7-fold at 70% (v/v) DSW medium, respectively. The EPS were proved to be glucose-rich polysaccharides and were able to increase proliferation and insulin secretary function of rat insulinoma RINm5F cells, in a dose-dependent manner. In addition, EPS also strikingly reduced the streptozotocin-induced apoptosis in RINm5F cells indicating the mode of the cytoprotective role of EPS on RINm5F cells.

The profile of enzymes relevant to solvent production during direct fermentation of sago starch by Clostridium saccharobutylicum P262 utilizing different pH control strategies

The profile of enzymes relevant to solvent production during direct fermentation of sago starch by Clostridium saccharobutylicum P262 in a 2 L stirred tank fermenter was determined utilizing different pH control strategies. During fermentation without pH control (initial pH of 6), the specific activity of crotonase, thiolase, and β-hydroxybutyryl-CoA dehydrogenase increased proportionally with solvent production. The highest crotonase (3,450.7 kat) and phosphotransbutyrylase activity (1,475.6 kat) was observed in fermentation where pH was maintained at 5 during the acidogenic phase and corresponded to a fairly high acid accumulation but low solvent production. During fermentation with a controlled pH of 5.25 during the sol-ventogenic phase, the highest thiolase specific activity (255.7 kat) was obtained and corresponded to the highest production of acetone. On the other hand, the highest specific activities of crotonase, β-hydroxybutyryl-CoA dehydrogenase, and phosphotransbutyrylase were observed at pH 5.5 and corresponded to the highest production of ethanol and butanol. Butyryl-CoA dehydrogenase had no significance role in solvent fermentation. These results suggested that pH control strategies were important for improvement of solvent production during direct fermentation of sago starch by C. saccharobutylicum.

Influence of pH and impeller tip speed on the cultivation ofBifidobacterium pseudocatenulatum G4 in a milk-based medium

Biomass production ofBifidobacterium pseudocatenulatum G4 in a milk-based medium was carried out in a 2- and 10-L stirred tank fermenters. The effects of impeller tip speed (0.28, 0.56, and 0.83 m/s) and pH control (6.0, 6.5, and 7.0) on the biomass production were investigated. The growth performance in the 2-L fermenter was significantly improved when the impeller tip speed was held constant at 0.56 m/s and the pH was controlled at 6.5. These conditions yielded a maximum biomass of 1.687×109 cfu/mL, a maximum specific growth rate of 0.504 h−1, a biomass productivity of 9.240×107 cfu/mL·h, and a biomass yield of 9.791×1010 cfu/g lactose. The consumption of milk lactose resulted in the accumulation of 7.353 g/L acetic acid and 6.515 g/L lactic acid, with an acetic:lactic ratio of 1.129. Scale-up of the fermentation process to a 10-L fermenter based on a constant impeller tip speed of 0.56 m/s yielded reproducible results with respect to biomass production and cell viability.

A kinetics study on the biodegradation of synthetic wastewater simulating effluent from an advanced oxidation process using Pseudomonas putida CECT 324

Bacterial growth on mixed substrates is employed for wastewater treatment. Biodegradation kinetics of Pseudomonas putida CECT 324 growth on formic acid, vanillin, phenol and oxalic acid mixtures is described. The experiments were carried out in a stirred-tank fermentor in batch mode at different temperatures (25, 30 and 35 °C) and pH (5, 6 and 7). The four compounds selected are typical intermediates in pesticide-contaminated water treated by advanced oxidation processes (AOPs). The toxicity of intermediates was investigated for a combined AOP-biological treatment, and the minimum DOC inhibitory concentration of the intermediate mixture was 175 ppm. The resulting biodegradation and growth kinetics were best described by the sum kinetics with interaction parameters (SKIP) model. Phenol and oxalic acid inhibit P. putida growth, and formic acid consumption strongly affects the biodegradation of oxalic acid. At all the temperatures tested and at pH between 5 and 7, P. putida CECT 324 was able to degrade the four substrates after culture times of 30 h at 30 °C and pH 7, which were the best conditions, and after 70 h, under the worst, at 35 °C.

High-density cultivation of oleaginous yeast Rhodosporidium toruloides Y4 in fed-batch culture

Microbial lipid production by the oleaginous yeast Rhorosporidium toruloides Y4 was studied using glucose as carbon source, in order to realize high-density cell culture. Batch cultures demonstrated that there was little inhibitory effect with a substrate concentration of up to 150 g l −1. Flask fed-batch cultures were run for 25 days and reached a dry biomass and cellular lipid content of 151.5 g l −1 and 48.0% (w/w), respectively. Using pilot-scale fed-batch cultures in a 15-l stirred-tank fermenter for 134 h resulted in dry biomass, lipid content and lipid productivity of 106.5 g l −1, 67.5% (w/w) and 0.54 g l −1 h −1, respectively. The fed-batch culture model used here featured initial nutrient-rich media and a pure carbon source with discontinuous feeding. Gas chromatography analysis revealed that lipids from R. toruloides Y4 contained mainly long-chain fatty acids with 16 and 18 carbon atoms. The four major constituent fatty acids were oleic acid, palmitic acid, stearic acid and linoleic acid. A slight increase in stearic acid production was found during the culture process. Based on these compositional data, microbial lipids from R. toruloides Y4 are a potential alternative oil resource for biodiesel production.

Biotransformation of various carbon sources to kojic acid by cell-bound enzyme system of A. flavus Link 44-1

The ability of cell-bound enzyme of Aspergillus flavus Link 44-1 for production of kojic acid was studied in resuspended cell system. Cell material was produced in batch fermentation using 2 L stirred tank fermenter. The cell mycelia were then resuspended into 250 mL shake flask containing various carbon sources solution. Among the carbon sources tested, glucose gave the highest kojic acid yield based on carbon consumed (0.365 g/g) followed by sucrose (0.279 g/g), starch hydrolysate (0.212 g/g) and fructose (0.195 g/g). The rate of biotransformation was increased with increasing mycelial cell. Kojic acid production was also varied with different glucose and sucrose concentrations. The highest production was obtained at 100 g/L glucose and 100 g/L sucrose with a final kojic acid concentration of 45.3 and 33.4 g/L, respectively. The rate of biotransformation of glucose and sucrose to kojic acid followed the Michaelis–Menten equation, suggesting that the biotransformation rate vary with substrate concentration similar to the behaviour of many enzymes reaction.

Enhanced production of lovastatin in a bubble column by Aspergillus terreus using a two‐stage feeding strategy

AbstractA two‐stage feeding strategy is shown to improve the rate of production of lovastatin by Aspergillus terreus when compared with conventional batch fermentation. The feeding strategy consisted of an initial batch/fed‐batch phase and a semi‐continuous culture dilution phase with retention of pelleted biomass in a slurry bubble column reactor. The batch phase served only to build up the biomass for producing lovastatin, a secondary metabolite that inhibits its own synthesis in the producing microfungus. The semi‐continuous dilution phase provided nutrients to sustain the fungus, but prevented biomass growth by limiting the supply of essential nitrogen. (Synthesis of lovastatin does not require nitrogen.) The preferred pelleted growth morphology that favors lovastatin synthesis was readily obtained and maintained in the 20 L bubble column used. In contrast, a stirred tank fermentation had a substantially lower production of lovastatin because mechanical agitation damaged the fungal pellets. The two‐stage feeding method increased lovastatin production rate by more than 50% in comparison with the conventional batch operation. Rheological data for the fungal broth are presented. Copyright © 2007 Society of Chemical Industry