Improvement of foam breaking and oxygen-transfer performance in a stirred-tank fermenter

This study examined a stirred-tank fermenter (STF) containing low-viscosity foaming liquids with an agitation impeller and foam-breaking impeller mounted on the same shaft. Results showed that the performance of the foam-breaking impeller can be improved by changing a conventional six-blade turbine impeller into a rod impeller as the agitation impeller. The volumetric oxygen-transfer coefficient, k _L a, in the mechanical foam-control method (MFM) using a six-blade vaned disk as the foam-breaking impeller in the STF with the rod impeller was approximately five times greater than that of the chemical foam-control method (CFM) adding an anti-foaming agent in the STF with the six-blade turbine impeller. Application of the present method to the cultivation of Saccharomyces cerevisiae K-7 demonstrated that the cultivation time up to the maximum cell concentration was remarkably shorter than that achieved using a conventional CFM.     

Conidiation ofNeurospora crassa in submerged culture without mycelial phase

Summary Conidia ofNeurospora crassa shaken in liquid cultures at 46°C for 15 h and then shifted-down to 25°C germinate directly into conidiophores producing new conidia (macroconidia).     

Conidiation of Hirsutella thompsonii var. synnematosa in submerged culture

Fourteen monosporal isolates of Hirsutella thompsonii grew vegetatively in various liquid media producing typical phialidic-like conidiophores. Hirsutella thompsonii var. synnematosa from Ivory Coast (HtIC) was the only pathotype which produced true conidia in submerged culture. HtIC began producing conidia after 3 days incubation reaching a peak ranging from 6.8 × 10⁵ to 9.7 × 10⁷ conidia/ml between 6 and 11 days. A concentration of 10 g/liter of corn steep liquor and 0.2% Tween 80 were essential for maximum conidiation. Submerged conidia had a smooth but somewhat rugose conidial walls, whereas aerially formed conidia were distinctly verrucose. Germination of submerged conidia ranged from 5.2 to 12.9% and were virulent causing 32.5% infection to adult citrus rust mites when sprayed on citrus foliage at 1.2 × 10⁹ conidia/ml.     

Photolithotrophic cultivation of Laminaria saccharina gametophyte cells in a stirred-tank bioreactor

Filamentous cell cultures derived from female gametophytes of the temperate brown macroalga Laminaria saccharina were photolithotrophically cultivated in artificial seawater medium within an illuminated 1.3-L stirred-tank bioreactor at 13 degrees C using CO(2) in air as the carbon source. A Monod model adequately described light-saturated growth. The apparent half-saturation constant (K(o)) was 23 muE/m(2)-s, and maximum specific growth rate was 0.15 day(-1). At a constant inoculation cell density of 50 mg DCW/L, biomass productivity after 26 days of cultivation increased from 630 mg DCW/L at 18 muE/m(2)-s to 890 mg DCW/L at 228 muE/m(2)-s. At 98 muE/m(2)-s, 1.1 vvm aeration rate, and 250 rpm impeller speed, the CO(2) transfer rates (CO(2) TRs) and CO(2) consumption rates (r(co(2) )) were determined over the cultivation period. At peak CO(2) demand, the maximum CO(2) TR was 0.19 mmol CO(2)/L-h, but r(co(2) ) was only 0.15 mmol CO(2)/L-h, implying that the culture was not CO(2) transport limited. This is the first reported bioreactor cultivation study of cell cultures derived from a macrophytic marine alga. (c) 1995 John Wiley & Sons, Inc.     

Decolorization of molasses by a new isolate of Geotrichum candidum in a jar fermenter

Decolorization of crude molasses by a newly isolated dye-decolorizing fungus, Geotrichum candidum Dec 1, was conducted in a jar fermentor system having fan-type propellers and a pressure swing adsorption oxygen generator. The oxygen-fortified air supply was effective not only to obtain a highest decolorization degree of 80% molasses but also the highest peroxidase activity which is responsible for the decolorization of the dyes. © Rapid Science Ltd. 1998     

High density cultivation of Anchusa officinalis in a stirred-tank bioreactor with in situ filtration

Previously, Su et al. [Biotechnol Bioeng 42: 884–890 (1993)] reported improved production of rosmarinic acid by Anchusa officinalis in shake-flask cultures using a cultivation strategy that involved intermittent medium exchange. Implementation of this cultivation strategy in 2.5-1 stirred-tank bioreactor cultures is investigated in the present study. Intermittent cell/medium separation in the bioreactor was accomplished by means of automated in situ culture filtration. In the bioreactor culture, rosmarinic acid production was found very sensitive to agitation and aeration conditions as well as dissolved oxygen concentration. A maximum cell density of 35 g dry weight/l and a rosmarinic acid concentration of 3.7 g/l were obtained by maintaining the dissolved oxygen concentration above 30% air saturation, gradually raising the impeller tip speed from 34 cm/s to 72 cm/s, and keeping the aeration rate at 0.44 vvm while increasing the O₂: air ratio in the gas feed stream to 4:1. This result is comparable with the data obtained from shake-flask cultures using the same culture strategy.     

Strategies to overcome foaming and wall-growth during the cultivation of Morinda elliptica cell suspension culture in a stirred-tank bioreactor

Strategies to overcome foaming and wall-growth during the cultivation of Morinda elliptica (Rubiaceae) cell suspension cultures in a stirred-tank bioreactor are described. Of all the strategies applied, only bubble-free aeration was successful in eliminating foaming by 100%. Despite the foaming effect of around 40% in G medium strategy with 0.012% (v/v) antifoam, the maximum dry cell weight attained (19.2 g l^-1) and anthraquinone (AQ) content (4.0 mg g^-1 DW) was nearly three times higher than that achieved in cultivation using 0.025% (v/v) antifoam. For continuous cell growth, the effect of inoculum age should also be considered when anti-foam is to be added. P medium strategy, without antifoam addition, not only promoted both growth (18 g l^-1) and AQ production (9.8 mg g^-1 DW), but also resulted in lower foaming and wall-growth (below 30% level), and higher foaming reduction (30–40%). This revised version was published online in June 2006 with corrections to the Cover Date.     

Dehydrogenase activity and toxinogenesis of a production strain ofCorynebacterium diphtheriae during submerged cultivation

A simple biochemical procedure was obtained for studying metabolism ofCorynebacterium diphtheriae during submerged cultivation based on the modification of the assay of dehydrogenase activity using 2,3,5-triphenyltetrazolium chloride as redox indicator. Results obtained by the estimation of the dehydrogenase activity using TTC are in a good accordance with oxygen consumption assayed manometrically. By following dehydrogenase activity in submerged cultivations of a production strain ofCorynebacterium diphtheriae PW8-Weissensee we found that a massive toxin production is connected with the decrease of the activity of cells. This fall of activity occurs yet during the exponential phase of growth. Especially a sudden fall of succindehydrogenase activity exactly indicates the beginning of a considerable toxin accumulation in the medium. The presence of inhibitory concentrations of iron ions in the medium not only increases the level of dehydrogenase activity but changes its whole kinetics. A retarded and irregular fall of the activity occurs instead of a sharp one typical for good toxin production.     

Conidiation of Neurospora crassa induced by treatment with natrium fluoride in submerged culture

Several strains of Rhizobium meliloti which have been subcultured for 23–33 years have changed from being markedly specific in their somatic agglutination reactions to become widely cross-reactive. On the other hand a fresh collection of the same species obtained from naturally nodulated, field-grown plants revealed the high degree of agglutinating specificity which had previously characterised the old-cultures. Attempts to reselect a specific substrain from old cross-agglutinating cultures by six plant passages, or to detect change to cross reactivity by ten successive subcultures of recent isolates were unsuccessful. However, one strain, isolated in 1939, was recently found to contain both specific and cross-reactive substrains. Practically all the cultures, both old and recent, showed considerable mutability in colony characteristics but none of these was consistently correlated with cross agglutinability. Instability in 6.4% (w/v) NaCl was characteristic of the cross-agglutinating cultures. Cross reactivity was associated with a shared lipopolysaccharide antigen (LPS) which appeared to be obscured by an outer antigen in most strains still showing specific agglutinability. In the exceptional case of strain SU27, agglutination could be attributed to its specific LPS.     

Influence of pH on the morphology ofTrichoderma reeseiqm 9414 in submerged culture.

The influence of pH on the germination characteristics and the microscopic morphology ofTrichoderma reesei QM 9414 has been investigated. The parameters of a kinetic model were estimated by fitting model simulations to morphological measurements during submerged cultures at different pH values. Both the tip extension rate and the branching frequency varied with the pH and had maximum values around pH 4.5. The time of spore germination was dependent on the pH, but within the used pH-range (2.2–7.6), no significant effect of pH on the fraction of viable spores was observed.     

Conidiation of Neurospora crassa induced by treatment with natrium fluoride in submerged culture.

A transient treatment of pregerminated conidia of Neurospora crassa with NaF induced young, submerged cultures to prematurely differentiate conidia. The inductive treatment decreased the rate of respiration (with lower RQ), reduced the relative concentration of nucleoside triphosphates, and inhibited leucine incorporation into protein and adenosine incorporation into RNA.     

Computer control of pH and DO in a laboratory fermenter using a neural network technique

In this contribution, the advantages of the artificial neural network approach to the identification and control of a laboratory-scale biochemical reactor are demonstrated. It is very important to be able to maintain the levels of two process variables, pH and dissolved oxygen (DO) concentration, over the course of fermentation in biosystems control. A PC-supported, fully automated, multi-task control system has been designed and built by the authors. Forward and inverse neural process models are used to identify and control both the pH and the DO concentration in a fermenter containing a Saccharomyces cerevisiae based-culture. The models are trained off-line, using a modified back-propagation algorithm based on conjugate gradients. The inverse neural controller is augmented by a new adaptive term that results in a system with robust performance. Experimental results have confirmed that the regulatory and tracking performances of the control system proposed are good.     

High concentration cultivation of Bifidobacterium longum in fermenter with cross-flow filtration

Summary High concentration cultivation of Bifidobacterium longum in a fermenter with cross-flow filtration using a ceramic filter is described. Continuous cross-flow filtration allowed complete recycling of the cells to the fermenter and also continuous separation of inhibitory metabolites. The final cell concentration attained in the cultivation was 54.4 g dry wt./l; this was seven times as high as that without cross-flow filtration. The time course of the cultivation with cross-flow filtration was predicted, based on the assumption that the specific growth rate can be expressed only as a function of concentrations of metabolites (acetate and lactate) in a culture broth.Nomenclature D dilution rate (h^-1) - m maintenance coefficient (h^-1) - OD ₅₇₀ optimal density at 570 nm - P _A acetate concentration (g/l) - P _A0 initial acetate concentration (g/l) - P _L lactate concentration (g/l) - P _L0 initial lactate concentration (g/l) - S lactose (substrate) concentration (g/l) - S ₀ initial lactose (substrate) concentration (g/l) - t cultivation time (h) - Y _x/s growth yield (g/g) - X dry cell concentration (g/l) - X ₀ initial dry cell concentration (g/l) - constant - constant     

Factors affecting the production of various gibberellins during submerged cultivation ofGibberella fujikuroi

Влияние условий культивирования на образование гиббереллинов при глубиннои ферментации Gibberella fujikuroi изучали с помощью хроматографии на бумаге гибберелловой кислоты и гиббе-реллина А прямо в ферментационной среде и путем определения характера выделенных кристаллических продуктов. При благоприятных условиях применявшийся нами продуктивный щтамм способен образовать и одну только гиббелловую кислоту, и ее смесь с гиббереллином А и В обоих случаях дает сравнительно высокий выход. Из факторов, определяющих качество возникаюшего активного метаболита, наиболее выразительное влияние оказывает состав ферментационной среды, в особенности качество источника азота. Наблюдалося однако и влияние некоторых других факторов, напр., исходного pH культуры и интенсивности аэрации. Кукурузный экстракт как источник азота в ферментационной среде окзывает выразительное влияние на образование гибберелловой кислоты. В средах с суспензией соевой или арашидовой муки, в условиях, благоприьтных для получения максимальной общей продук-ции гиббереллинов, наблюдается образование смеси гибберелловой кислоты и гиббереллина А.     

High concentration cultivation of Bifidobacterium bifidum in a submerged membrane bioreactor

In batch cultures, after 25 h, the maximum cell mass of Bifidobacterium bifidum BGN4 was 4.5 g/L, and the maximum cell count was 3.0 x 10(9) cfu/mL at pH 6.0 and 50 g/L sucrose. To increase the viable counts of bifidobacteria, cell retentive culture was applied using a submerged membrane bioreactor with suction and gas sparging. The maximum mass, count, and productivity of the cells after 36 h were 12.0 g/L, 2.2 x 10(10) cfu/mL, and 6.1 x 10(8) cfu/mL x h, respectively, at the feeding (dilution) rate of 120 mL/h (0.06 h-1) in the feeding medium. The accumulated levels of organic acids and ammonium ions at the end of the cultivation were 1.5 and 1.0 g/L, respectively. The viable counts and volumetric productivity of the cells after the cell retentive culture were 7.3- and 5.1-fold higher, respectively, than the values obtained during batch culture. These high viable counts and volumetric productivities were obtained by maintaining lower concentrations of organic acids and ammonium ions so that the growth of B. bifidum BGN4 was not inhibited. The submerged membrane bioreactor produced the highest viable counts of B. bifidum without membrane fouling and cell damage.     

Uptake of inorganic and organic nutrient species during cultivation of a Chlorella isolate in anaerobically digested dairy waste

A natural assemblage of microalgae from a facultative lagoon system treating municipal wastewater was enriched for growth in the effluents of an anaerobic digester processing dairy waste. A green microalga with close resemblance to Chlorella sp. was found to be dominant after multiple cycles of sub‐culturing. Subsequently, the strain (designated as LLAI) was isolated and cultivated in 20× diluted digester effluents under various incident light intensities (255–1,100 µmoles m^?2 s^?1) to systematically assess growth and nutrient utilization. Our results showed that LLAI production increased with increasing incident light and a maximum productivity of 0.34 g L^?1 d^?1 was attained when the incident irradiance was 1,100 µmoles m^?2 s^?1. Lack of growth in the absence of light indicated that the cultures did not grow heterotrophically on the organic compounds present in the medium. However, the cultures were able to uptake organic N and P under phototrophic conditions and our calculations suggest that the carbon associated with these organic nutrients contributed significantly to the production of biomass. Overall, under high light conditions, LLAI cultures utilized half of the soluble organic nitrogen and >90% of the ammonium, orthophosphate, and dissolved organic phosphorus present in the diluted waste. Strain LLAI was also found to accumulate triacylglycerides (TAG) even before the onset of nutrient limitation and a lipid productivity of 37 mg‐TAG L^?1 d^?1 was measured in cultures incubated at an incident irradiance of 1,100 µmoles m^?2 s^?1. The results of this study suggest that microalgae isolates from natural environments are well‐suited for nutrient remediation and biomass production from wastewater containing diverse inorganic and organic nutrient species. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1336–1342, 2016     

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Measurements of oxygen transfer were made during cultivation of the yeast Saccharomyces cerevisiae in a 90–250 litre working volume concentric tube airlift fermenter. Results demonstrated that the rate of oxygen transfer varies with position in the fermenter, being higher in the riser and top-section than in the downcomer and lowest near the base of the fermenter. The time for liquid circulation was generally smaller than the time constant for oxygen transfer (1/k_La) indicating that the rate of oxygen transfer was slow compared to the rate of liquid movement. Measured dissolved oxygen concentrations therefore did not represent the equilibrium arising from the balance between the rates of oxygen transfer and oxygen depletion. Hence measuredk _L a values were not representative of local oxygen transfer conditions but instead were indicators of the rate of mass transfer the liquid flow had encountered prior to reaching the point of measurement. Generally the individual rates of oxygen transfer in the vessel were found to increase with increasing vessel height.     

At-line monitoring of a submerged filamentous bacterial cultivation using near-infrared spectroscopy

The use of near infra-red spectroscopy (NIRS) to monitor a submerged filamentous bacterial bioprocess was investigated. An industrial strain of the filamentous bacterium Streptomyces fradiae was cultured in a 12 litre stirred tank reactor (STR) using a complex medium. This mycelial 4 phase (oil, water, gas and solid) system produced highly complex and variable matrices, therefore monitoring such a complex fluid with NIRS represented a considerable challenge. Nevertheless, successful models for four key analytes (methyl oleate, glucose, glutamate and ammonium) were built at-line (rapid off-line) using NIRS. In the present study, the methods used to formulate, select and validate the models for the key analytes are discussed, with particular emphasis on how the model performance can be critically evaluated. Since previous reports on NIRS in monitoring bioprocesses have either involved simpler matrices, or, in filamentous systems, have not discussed how NIRS models can be critically assessed, the emphasis in the present study on providing an insight into the modelling process in such a complex matrix, may be particularly important to the applicability of NIRS to such industrial bioprocesses.