The growth rate and the maximum cell concentration of methanotrophic bacteria are limited by the transfer of methane and oxygen to the culture fluid. The operation under moderate pressure results in an increase in driving force for the mass transfer of both nutrients and, therefore, in a large increase in the attainable biomass concentration. Our laboratory pressure fermenter with a volume of 12 litres operates under a system pressure of up to 0.5 MPa. In this reactor a maximum productivity of 6 g biomass/lh is achieved. However, operating under moderate system pressure and exhaust gas recycling has also disadvantages because the concentrations of the gas phase components may inhibit the growth process. From the results of the laboratory fermenter we have developed kinetic models of the influence of dissolved oxygen and carbon dioxide on the specific growth rate of the methanotrophic strain GB 25. These models are the basis for processing under increased system pressure and exhaust gas recycling.
Addition of oxygen-containing C1-compounds to chemostat cultures of GB 25 increases both the yield of biomass and the specific growth rate. At optimum concentrations the catalytic activity of these compounds increases with increasing growth rates. Their influence on maintenance coefficients and maximum yield coefficients decreases in the order CH3OH greater than CO2 greater than HCOOH greater than HCHO. This result together with spectrophotometric NADH determinations suggests that the NADH pool determines the balance between the assimilatory and oxidative utilization of formaldehyde.
The influence of different concentrations of magnesium, pot,assium, phosphorus and copper on the growth kinetics of the methanotrophic bacterium GB 25 was investigated. Diverse inhibition models were used for the mathematical description of the results. On the basis of these model equations the optimal concentrations of the investigated ions were derived. Copper causes the greatest inhibition, on the contrary, potassium practically does not inhibit the growth of bacterium GB 25. KinetischeUntersuchungen zum Bedarf an Mineralsalzen, d. h. die Untersuchung des Einflusses der Konzentration einzelner Komponenten des Nahrmediums auf die Wachstumsgeschwindigkeit oder andere Kennziffern des Kultivierungsprozesses von Mikroorganismen, stellen eine wichtige Forschungsaufgabe dar. Durch die Bearbeitung dieser Problemstellung wird es moglich, limitierende und inhibierende Einflusse auf den WachstumsprozeR quantitativ zu ermitteln und ein technologisches Regime fur eine effektive ProzeBfiihrung beziiglich der Mineralstoffversorgung der Mikroorganismen zii erarbeiten. Das Ziel der vorliegenden Arbeit bestand darin, fiir einige ausgewahlte Ionen die optimalen Konzentrationen fur das Wachstum eines methanotrophen Bakterienstammes zu ermitteln sowie die Limitations-und Inhibierungsbereiche zu charakterisieren. Die inhibierende Wirkung uberschussiger Mineralsalze auf das Wachstum methanoxidierender Kulturen wird in der Literatur diskutiert [ 11. Besondere Aufmerksamkeit wird dabei auf die Konzentration von Ammonium-und Kitrationen gelenkt [2-41. Die Limitation des Wachstums methanoxidierender Bakterien durch Kaliumionen und Phosphat wurde durch DWORKIN und FOSTER [5] und STOUTHAMER [6] dargestellt. HARRISON et al. [7] untersuchten die stimulierende und inhibierende Wirkung von sog. Mikroelementen. Die Inhibierung kann bis zur vollstandigen Unterdruckung des Wachsturns fiihren, wobei der Konzentrationsbereich zwischen Stimulierung und Inhibierung fur einige Metalle sehr klein sein kann und je nach Stamm eine unterschiedliche Empfindlichkeit gegenuber Metallionen beobachtet wird [8]. Unter den sogenannten Mikroelementen nimmt Kupfer eine exponierte Stellung ein, da es eine wesentliche Rolle im Metabolismus von Mikroorganismen spielt. ober die Notwendigkeit von Kupfer fur das Wachstum methanutilisierender Mikroorganismen gibt es Mitteilungen mit gegensatzlichem Charakter. So wurde einerseits vorgeschlagen, es wegen seiner stark wachstumshemmenden Wirkung iiberhaupt nicht als Bestandteil des
Added C1-compounds of the intermediates methanol, formaldehyde, formate and carbon dioxide show a catalytic effect on the growth rate and cell yield of CH4-assimilating bacteria GB 25 with serine pathway. Maximum stimulation is obtained by added amounts of about 20 mg C1-compound/g bacteria dry matter. The influence of C1-compounds decreases as follows: methanol greater than carbon dioxide greater than formate greater than formaldehyde.
Added C,-compounds of the intermediates methanol, formaldehyde, formate and carbon dioxide show a catalytic effect on the growth rate and cell yield of CH,-assimilating bacteria GB 25 with serine pathway.Maximum stimulation is obtained by added amounts of about 20 mg C,-compound/g bacterix dry matter. The influence of C,-compounds decreases as follows: methanol > carbon dioxide > formate > formaldehyde.
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