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.

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.