Dissolved Oxygen Tension Levels Research Articles

Different responses in the expression of alginases, alginate polymerase and acetylation genes during alginate production by Azotobacter vinelandii under oxygen-controlled conditions.

Alginate production and gene expression of genes involved in alginate biosynthesis were evaluated in continuous cultures under dissolved oxygen tension (DOT) controlled conditions. Chemostat at 8% DOT showed an increase in the specific oxygen uptake rate [Formula: see text] from 10.9 to 45.3mmolg-1h-1 by changes in the dilution rate (D) from 0.06 to 0.10h-1, whereas under 1% DOT the [Formula: see text] was not affected. Alginate molecular weight was not affected by DOT. However, chemostat at 1% DOT showed a downregulation up to 20-fold in genes encoding both the alginate polymerase (alg8, alg44), alginate acetylases (algV, algI) and alginate lyase AlgL. alyA1 and algE7 lyases gene expressions presented an opposite behavior by changing the DOT, suggesting that A. vinelandii can use specific depolymerases depending on the oxygen level. Overall, the DOT level have a differential effect on genes involved in alginate synthesis, thus a gene expression equilibrium determines the production of alginates of similar molecular weight under DOT controlled.

Effect of Oxygen Tension and Medium Components on Monomer Distribution of Alginate.

Alginate is a natural biopolymer composed of mannuronic and guluronic acid monomers. It is produced by algae and some species of Azotobacter and Pseudomonas. This study aims to investigate the effect of dissolved oxygen tension (DOT) and growth medium substrate and calcium concentrations on the monomeric composition of alginate produced by Azotobacter vinelandii ATCC® 9046 in a fermenter. Results showed that alginate production increased with increasing DOT from 1 to 5%. The highest alginate production was obtained as 4.51g/L under 20g/L of sucrose and 50mg/L of calcium at 5% DOT. At these conditions, alginate was rich in mannuronic acid (up to 61%) and it was particularly high at low calcium concentration. On the other hand, at extreme conditions such as high DOT level (10% DOT) and low sucrose concentration (10g/L), guluronic acid was dominant (ranging between 65 and 100%).

An Integrated Control Strategy for the Fermentation of the Marine-Derived Fungus Aspergillus glaucus for the Production of Anti-cancer Polyketide

An integrated control strategy of pH, shear stress, and dissolved oxygen tension (DOT) for fermentation scale-up of the marine-derived fungus Aspergillus glaucus HB 1–19 for the production of the anti-cancer compound aspergiolide A was studied. Keeping initial pH of 6.5 and shifting pH from 6.0 to 7.0 intermittently during the production phase greatly facilitated biosynthesis of aspergiolide A in shake flask cultures. Thus, a pH-shift strategy was proposed that shifting pH to 7.0 once it went lower than 6.0 by pulsed feeding NaOH solution during the production phase in bioreactor fermentation of A. glaucus HB 1–19. As a result, aspergiolide A production in a 30-L bioreactor was increased to 37.6 mg/L, which was 48.6% higher than that in 5-L bioreactor without pH shift. Fermentation scale-up was then performed in a 500-L bioreactor on the basis of an integrated criterion of near-same impeller tip velocity of early phase, DOT levels, and pH shift. The production of aspergiolide A was successfully obtained as 32.0 mg/L, which was well maintained during the process scale-up. This work offers useful information for process development of large-scale production of marine microbial metabolites.

Effects of dissolved oxygen and pH levels on weissellin A production by Weissella paramesenteroides DX in fermentation

Experiments carried out with the dissolved oxygen tension (DOT) maintained during fermentation at 0, 10, 50, 70 and 100% showed a direct effect of the dissolved oxygen levels on weissellin A production with no correlative increase on biomass. An estimate of the yield of weissellin A per gram biomass revealed the 50% DOT level as the optimum for increased yields. The effect of pH was studied in experiments carried out without pH control, with pH initially set at 6.0, 5.0 and 4.5 and with pH controlled at 6.0, 5.0 and 4.5. The initial pH value and the pH-drop gradient appear to be the important parameters for weissellin A production. Production was significantly higher with the uncontrolled initial pH compared to that of the controlled initial pH at 6.0, while acidic initial pHs created unfavorable conditions for production. Maintaining a constant pH environment during fermentation led to decreased production levels.

Factors Affecting Poly(3-hydroxybutyrate) Production from Oil Palm Frond Juice byCupriavidus necator(CCUG52238T)

Factors influencing poly(3-hydroxybutyrate) P(3HB) production by Cupriavidus necator CCUG52238T utilizing oil palm frond (OPF) juice were clarified in this study. Effects of initial medium pH, agitation speed, and ammonium sulfate (NH4)2SO4 concentration on the production of P(3HB) were investigated in shake flasks experiments using OPF juice as the sole carbon source. The highest P(3HB) content was recorded at pH 7.0, agitation speed of 220 rpm, and (NH4)2SO4 concentration at 0.5 g/L. By culturing the wild-type strain of C. necator under the aforementioned conditions, the cell dry weight (CDW) and P(3HB) content obtained were 9.31 ± 0.13 g/L and 45 ± 1.5 wt.%, respectively. This accounted for 40% increment of P(3HB) content compared to the nonoptimized condition. In the meanwhile, the effect of dissolved oxygen tension (DOT) on P(3HB) production was investigated in a 2-L bioreactor. Highest CDW (11.37 g/L) and P(3HB) content (44 wt.%) were achieved when DOT level was set at 30%. P(3HB) produced from OPF juice had a tensile strength of 40 MPa and elongation at break of 8% demonstrated that P(3HB) produced from renewable and cheap carbon source is comparable to those produced from commercial substrate.

Effect of Various Process Parameters on Morphology, Rheology, and Polygalacturonase Production by Aspergillus sojae in a Batch Bioreactor

The effects of pH, agitation speed, and dissolved oxygen tension (DOT), significant in common fungal fermentations, on the production of polygalacturonase (PG) enzyme and their relation to morphology and broth rheology were investigated using Aspergillus sojae in a batch bioreactor. All three factors were effective on the response parameters under study. An uncontrolled pH increased biomass and PG activity by 27% and 38%, respectively, compared to controlled pH (pH 6) with an average pellet size of 1.69 +/- 0.48 mm. pH did not significantly affect the broth rheology but created an impact on the pellet morphology. Similarly, at constant agitation speed the maximum biomass obtained at 500 rpm and at 30 h was 3.27 and 3.67 times more than at 200 and 350 rpm, respectively, with an average pellet size of 1.08 +/- 0.42 mm. The maximum enzyme productivity of 0.149 U mL-1 h-1 was obtained at 200 rpm with an average pellet size of 0.71 +/- 0.35 mm. Non-Newtonian and pseudoplastic broth rheology was observed at 500 rpm agitation speed, broth rheology exhibited dilatant behavior at the lower agitation rate (200 rpm), and at the medium agitation speed (350 rpm) the broth was close to Newtonian. Furthermore, a DOT range of 30-50% was essential for maximum biomass formation, whereas only 10% DOT was required for maximum PG synthesis. Non-Newtonian shear thickening behavior (n > 1.0) was depicted at DOT levels of 10% and 30%, whereas non-Newtonian shear thinning behavior (n < 1.0) was dominant at 50% DOT. The overall fermentation duration (50-70 h) was considerably shorter compared to common fungal fermentations, revealing the economic feasibility of this particular process. As a result this study not only introduced a new strain with a potential of producing a highly commercially significant enzyme but also provided certain parameters significant in the design and mathematical modeling of fungal bioprocesses.

Improvement in Production and Quality of Gellan Gum by Sphingomonas paucimobilis Under High Dissolved Oxygen Tension Levels

The effect of agitation rate and dissolved oxygen tension (DOT) on growth and gellan production by Sphingomonas paucimobilis was studied. Higher cell growth of 5.4 g l(-1) was obtained at 700 rpm but maximum gellan (15 g l(-1)) was produced at 500 rpm. DOT levels above 20% had no effect on cell growth but gellan yield was increased to 23 g l(-1 )with increase in DOT level to 100%. Higher DOT levels improved the viscosity and molecular weight of the polymer with change in acetate and glycerate content of the polymer.

Evaluation of the effects and interactions of mixing and oxygen transfer on the production of Fab’ antibody fragments in Escherichia coli fermentation with gas blending

Fermentations carried out at 450-L and 20-L scale to produce Fab' antibody fragments indicated a serious problem to control levels of dissolved oxygen in the broth due to the large oxygen demand at high cell densities. Dissolved oxygen tension (DOT) dropped to zero during the induction phase and it was hypothesised that this could limit product formation due to inadequate oxygen supply. A gas blending system at 20-L scale was employed to address this problem and a factorial 2(2) experimental design was executed to evaluate independently the effects and interaction of two main engineering factors: agitation rate and DOT level (both related to mixing and oxygen transfer in the broth) on Fab' yields. By comparison to the non-gas blending system, results in the gas blending system at same scale showed an increase in the production of Fab' by 77% independent of the DOT level when using an agitation rate of 500 rpm level and by 50% at an agitation rate of 1,000 rpm with 30% DOT. Product localisation in the cell periplasm of >90% was obtained in all fermentations. Results obtained encourage further studies at 450-L scale initially, to evaluate the potential of gas blending for the industrial production of Fab' antibody fragments.

Synthesis of extracellular (1 → 3)- and (1 → 6)-β-glucanase activities in carbon limiting chemostat culture by the fungus Acremonium sp. IMI 383068

When Acremonium sp. IMI 383068 was grown under chemostat conditions with scleroglucan as sole carbon source, the fungus produced four (1 → 3)-β-glucanases and a single (1 → 6)-β-glucanase. Production of the (1 → 3)-β-glucanase was growth rate related while the (1 → 6)-β-glucanase was growth rate unrelated. Specific activities of both were affected by increasing agitation speed, independently of dissolved oxygen tension (DOT) or growth rates, falling at the higher speeds examined. They also increased as DOT levels increased. No evidence was obtained to substantiate any relationship between enzyme specific activities and hyphal branching frequencies.

The effect of dissolved oxygen concentrations on (1 → 3)- and (1 → 6)-β-glucanase production by Acremonium sp. IMI 383068 in batch culture

The influence of dissolved oxygen tension (DOT) on the production of extracellular (1 → 3)- and (1 → 6)-β-glucanases by the fungus Acremonium sp. IMI 383068 was investigated in batch culture. The controlled DOT levels at which cultures were grown affected the measured (1 → 3)-β-glucanase specific activities, but these effects were less marked on the measured (1 → 6)-β-glucanase specific activities. There appeared to be no direct link between the branching frequency of the fungus as reflected by its hyphal growth unit, and changing DOT levels. Whether pustulan or scleroglucan were used as the sole carbon source also affected production of these enzymes and their response to varying DOT. The measured (1 → 3)-β-glucanase specific activities were generally higher with scleroglucan, mainly because of the production of an extra active (1 → 3)-β-glucanase whereas pustulan grown cells produced a corresponding inactive protein with an identical electrophoretic mobility by SDS-PAGE and N-terminal amino acid sequence. With pustulan grown cells, DOT levels had comparatively little influence on the optimal measured specific activities of the (1 → 3)-β-glucanases, while with scleroglucan, they increased as DOT increased.

The production of hemicellulases by Thermomyces lanuginosus strain SSBP: influence of agitation and dissolved oxygen tension.

Shake-flask cultivation of T. lanuginosus strain SSBP on coarse corn cobs yielded beta-xylanase levels of 56,500 nkat/ml at 50 degrees C, whereas other hemicellulases (beta-xylosidase, beta-glucosidase, and alpha-L-arabinofuranosidase) were produced at levels less than 7 nkat/ml. Cultivation on D-xylose yielded much lower levels of xylanase (350 nkat/ml), although other hemicellulase levels were similar to those produced on corn cobs. The influence of agitation rate and dissolved oxygen tension (DOT) on hemicellulase production was studied further in a bioreactor. On xylose, xylanase activities of 4,330 nkat/ml and 4,900 nkat/ml were obtained at stirrer speeds up to 1,400 rpm to control DOT. At a constant stirrer speed of 400 rpm, xylanase activities of 10,930 nkat/ml and 15,630 nkat/ml were obtained when cultivated on xylose and beechwood xylan respectively, despite DOT levels below 5% for the duration of fermentation. The results indicate that there is an interaction between agitation rate and DOT, impacting on xylanase and accessory enzyme production. Higher agitation rates favoured the production of xylosidase, arabinofuranosidase and glucosidase by T. lanuginosus strain SSBP, whereas the lower agitation rates favoured xylanase production. Rheological difficulties precluded cultivation on corn cobs in the bioreactor. Volumetric xylanase productivities of 1,060,000 nkat/l x h and 589,000 nkat/l x h obtained on beechwood xylan and xylose indicate that T. lanuginosus strain SSBP is a hyperxylanase producer with considerable industrial potential.

Aeration and yeast extract requirements for kojic acid production by Aspergillus flavus link

Growth and kojic acid production by Aspergillus flavus Link 44-1 were studied at different levels of dissolved oxygen tension (DOT) using a 2-l stirred tank fermenter. In all experiments, agitation was fixed at 600 rpm and DOT was controlled at different levels by varying airflow rates. Single-phase DOT control at three different levels (30, 50, and 80% saturation) did not enhance kojic acid production when compared to fermentation without DOT control (13.5 g l -l). The production of kojic acid in a fermentation with single-phase DOT control at 80% was comparable to that of a fermentation without DOT control. Decreased DOT levels below 80% reduced the production of kojic acid significantly although the biomass increased. When DOT was controlled at a very high level (80%) during active growth and then decreased to a low level (30%) during the production phase (i.e., two-phase DOT control), the production of kojic acid (28.9 g l -l) was increased by about two times compared to a fermentation without DOT control; however, when yeast extract was added continuously in a fermentation with two-phase DOT control, active growth occurred during the production phase and the maximum accumulation of kojic acid was reduced significantly. High DOT during on active growth phase and no addition of yeast extract during the production phase were required to enhance kojic acid biosynthesis. The most effective control strategy for kojic acid production, therefore, was to control DOT at very high levels during active growth and not add a nitrogen source during the production phase while using low levels of DOT.

Effect of the dissolved oxygen tension during cultivation of X. campestris on the production and quality of xanthan gum

The effect of the dissolved oxygen tension (DOT) on the production and quality of xanthan gum was studied in a range of 10% to 100% of saturation. Oxygen tension was controlled by gas blending in a well-mixed bioreactor. The evolution of the power law rheological indexes, as well as the apparent yield stress of the medium, was determined. Pyruvic acid residues were quantified in the xanthan produced. The mean molecular weight (MMW) was estimated by a rheological technique and the molecular weights distribution was estimated by gel permeation chromatography. Pyruvic acid content was higher as cultivation evolved. Pyruvate was very similar when oxygen tension was high (> 40% DOT), but showed a higher value if compared with 10% DOT. DOT strongly determines the rheological behaviour of the culture medium. The quality of xanthan was influenced by the DOT level. A saturation-type behaviour exists between the oxygen tension and the mean molecular weight. Micromixing could be playing a role in determining this behaviour. MMWs of 10×10 6 kg kgmol −1 were found above 40% DOT. In general, the proportion of high molecular weight polymers was higher as DOT was higher.

D-xylose fermentation by Candida shehatae and pichia stipitis at low dissolved oxygen levels in fed-batch cultures

The fermentation of D-xylose byCandida shehatae andPichia stipitis was studied in fed-batch fermentations using dissolved oxygen tension (DOT) control in the range of 0.2 to 1.4% air saturation. The response of these two yeasts to DOT was significantly different. Whereas the ethanol yield withC. shehatae was 0.35 to 0.38 g.g−1 at all DOT levels, that ofP. stipitis decreased from 0.44 at a zero DOT reading to 0.19 g.g−1 at 1.4% DOT.

Investigations of oxygen transfer into Penicillium chrysogenum pellets by microprobe measurements

A microcoaxial needle sensor with a tip diameter of ca. 0.7 microm was used as a microprobe to measure profiles of dissolved oxygen tension (DOT) within fixed pellets of Penicillium chrysogenum as a function of the DOT level around the pellet, in the presence and absence of bulk convective flow and turbulence. The investigations indicate that the oxygen transfer mechanism is complex. The results were interpreted by assuming the penetration convective flow into the entire pellet and penetration of turbulence into the outer range. A model was developed which was able to describe the measured DOT profiles very well. The model takes into account molecular and turbulent diffusion as well as convective flow as transfer mechanisms inside of the pellet. Structures of pellets used for microprobe measurements were evaluated by histological investigations. Considerable variations of mycelial density with radius within the pellets were found.