Influence of increased dissolved oxygen concentration on productivity and selectivity in cultures of a colabomycin-producing strain of Streptomyces griseoflavus.

The influence of enhanced O2 concentration on growth and formation of secondary metabolites by Streptomyces griseoflavus (strain Tü 2880) was investigated in a stirred tank and in an air-lift fermentor. At a partial pressure of O2 Po2 = 1880 mbar the growth was lowered by 50% compared to Po2 = 210 mbar, whilst substrate consumption and O2 uptake rate increased markedly. Production of the colabomycin complex reached maximum values at Po2 = 630 mbar. A similar increase of secondary metabolite formation was obtained when glycerol or acetate were fed at Po2 = 220 mbar. The portion of the derivate colabomycin A in the product mixture rose from 43% at Po2 = 210 mbar to 73% at Po2 = 1260 mbar. Since dissolved O2 concentration has a significant influence on productivity and selectivity it may be used to regulate aerobic fermentation processes.

Influence of increased dissolved oxygen concentration on the formation of secondary metabolites by manumycin-producing Streptomyces parvulus.

The influence of increased dissolved O2 concentrations (DOC) on cell growth and production of the secondary metabolite manumycin by a strain of Streptomyces parvulus (Tü 64) was investigated in a stirred tank fermentor. DOC is given as the O2 partial pressure (po2) in the gas phase in an equilibrium state with the liquid phase. Growth of S. parvulus was not influenced up to DOC equivalent to po2 = 1260 mbar. At po2 = 2205 mbar the maximum biomass concentration was lowered by 40%. Production of manumycin was markedly influenced by DOC and reached the maximal concentration at po2 = 315 mbar. At increased DOC three new metabolites were observed. Two of them, 64p-A and 64p-B, were identified as carboxamides, which represent the branched side chain of the manumycin molecule and a derivative with a shorter chain length. The third metabolite, 64p-C, was a manumycin derivative containing an aromatic ring system. Feeding of glycerol during the production phase increased the total yield and showed a similar effect of DOC. Since DOC has significant regulation effects on product formation and selectivity, it should be used as a major parameter in development strategies of aerobic microbial processes.

Influence of constant and oscillating dissolved oxygen concentrations on keto acid production by Gluconobacter oxydans subsps. melanogenum.

Gluconobacter species are known to oxidise glucose via a direct oxidation pathway which is distinct from the pentose phosphate pathway. In the present communication results of an investigation on the influence of different dissolved oxygen concentrations (DO) on the production of 2,5-diketogluconic acid in batch and chemostat cultures are given. DO of 30% relative to air at 1 bar was found as a threshold level for optimum productivity. The positive influence of continuous availability of dissolved oxygen on the process of rapid glucose oxidation was unambiguously shown as the result of induction of membrane bound dehydrogenases involved in direct glucose oxidation. Furthermore data of scale-down experiments in which the organism was cultivated under oscillations of dissolved oxygen, are given. The influences of such oscillations of DO in the region of the established threshold (30% saturation) were found to result in a prolonged lag phase for growth and product formation. The data obtained in this study revealed critical residence times at low DO that could be employed as a criterion for scale up of this aerobic process.

Influence of total and oxygen partial pressure on growth and metabolism of Methylomonas clara.

The effect of total and oxygen partial pressure on metabolic activities of Methylomonas clara has been investigated in batch and continuous cultivation experiments using a pressurizable airlift loop reactor. At Oxygen partial pressures of more than 1000 mbar growth of M. Clara is retarded and completely inhibited at 1200 mbr. However, after several hours of incubation at elevated oxygen partial pressures, biomass formation is nearly doubled in subsequent continuous operation, Cells pretreated with oxygen are characterized by a change of cytochrome content; they excrete carboxylic acids into the medium. The results indicate that, by sparging an aerobic culture intermittently with pure oxygen, formation of biomass might be enhanced.

Selective recycle of viable animal cells by coupling of airlift reactor and cell settler.

A new system for the perfusion culture of animal cells in suspension is described. It consists of an airlift loop reactor and a settling tank for cell retention. Insufficient nutrient and oxygen supply of the cells in the settling tank was prevented by cooling the cell suspension before entering the settler. As a result, the catabolic activity of the cells in the settler was reversibly reduced. Furthermore, the density gradient induced by cooling caused a liquid motion through the settler. Thus, it was not necessary to pump medium containing shear, sensitive cells. With this simple system, it was possible to prduce 2 to 5 g of antibodies in a 5.4-L reactor in continuous runs of 400 to 600 h. The productivity was increased by a factor of 17 and the cell density was 4 times higher in comparison with the corresponding batch system. The cell retention system was found to have the property of separating viable and nonviable cells. With the increasing perfusion rate, dead cells and debris were preferably washed out. For perfusion rates up to 1.3 d(-1), the retention efficiency of the settler was nearly 100% for viable cells; hence, this system may show advantages at the industrial scale.

Batch and continuous cultivation of Pseudomonas fluorescens at increased pressure.

The effect of increased total pressure and partial pressures of oxygen and carbon dioxide on the growth of Pseudomonas fluorescens was investigated in an airlift reactor. In batch cultivations bacterial growth was completely inhibited with air at 8 bars total pressure. The same effect was observed with aeration by pure oxygen at 1.15 bars. Carbon dioxide partial pressure did not show inhibitory effects. Continuous experiments confirm the assumption that growth inhibition at higher total pressure is caused by the increase in oxygen partial pressure. Incubation of P. fluorescens at higher oxygen partial pressure led to an increase of bacterial productivity during subsequent continuous cultivation at ambient pressure (1 bar) with air. Maximum productivity was increased by about 75% after aeration with pure oxygen. This effect is probably the result of metabolic adaption of the bacterial cells to high oxygen partial pressure.

Growth and product formation of actinomycetes cultivated at increased total pressure and oxygen partial pressure.

Influence of pressure (P) and oxygen partial pressure (PO2) on cultivation of various Streptomyces spp. and Micromonospora purpurea was examined in pressurized air-lift and stirred tank fermenters. The maximum PO2 was 2100 mbar. Growth and product formation of all cultures tested were markedly influenced by PO2 higher than 1000 mbar. There is evidence that wild strains are more oxygen tolerant than production strains. At a certain PO2 the metabolic activities of all cultures were inhibited. However, results obtained with S. aureofaciens and S. rimosus indicated an increase in specific product formation rate at elevated pressure. With increase in oxygen tension incorporation of oxygen into tetracycline molecules was enhanced. Since elevated oxygen tension can either show inhibiting effects or may be used for regulation of product formation and selectivity, the influence of PO2 should be determined in an appropriate experimental set-up for each process.

Effect of total and partial pressure (oxygen and carbon dioxide) on aerobic microbial processes.

In industrial bioreactors, levels and gradients of total and partial pressures are considerably higher than on the laboratory scale. In the relevant range (in general up to 2 or 3 bar, maximum approx. 10 bar), effects of total pressure on aerobic cultures are negligibly small. CO2 partial pressures of more than approx. 100 mbar may have inhibitory effects on aerobic cultures. Growth of aerobic cultures can be enhanced by O2 partial pressures higher than 210 mbar (corresponding to air at 1 bar), if oxygen transfer is limited. In many cases, however, increased O2 partial pressure (higher than approx. 1 bar) is toxic to aerobic cultures and inhibits microbial growth and product formation. Stepwise and cyclic variations of O2 partial pressure may have positive or negative effects, depending on strain of microorganism, culturing conditions, and range of dissolved oxygen concentration. Knowledge of these effects is required in process development and bioreactor scale-up.

Oxygen transfer from gas bubble into liquid.

Oxygen transfer from a gas bubble into the surrounding liquid is examined by measuring oxygen pressure with Po2-needle electrodes at different distances from the bubble. From there, the mass transfer coefficient can be calculated. First measurements yielded results in the range to be expected.