Alkene-utilizing bacteria have been employed for producing Microorganisms epoxides from gaseous alkenes in either gas-solid' or multiphase bioreactors .2,3 Such organisms contain an inducible alkene mono-oxygenase and consequently need to be cultivated on gaseous substrates such as either ethene or propeneThe isolation and characterization of the ethene-utilizing ~ycobacterium E3 and the propene-utilizing Xanthobacter Py2 used in this study has been described previously. 'OJ* when they are used for the production of 1,2-epoxyaIkanes. Growing bacteria on gaseous substrates presents some special problems and these have been discussed by Barnes Cultivation of Microorganisms et al.4 who cultivated methane-utilizing bacteria in chemostats. Particular attention must be paid to the cultivation system employed because, in case of a gaseous substrate, accurate measurements are more difficult than with either miscible liquid or solid substrates. Moreover, the kinetics of gas transfer has to be included when modelling growth kinetics on gaseous substrates. Work with chemostat systems for the growth of bacteria on gaseous substrates has been limited to methane-utilizing bacteria."' To estimate growth parameters of methane-utilizing bacteria in a chemostat culture, Nagai and co-workers' used an apparatus in which methane was supplied dissolved in the mineral salts medium, but in all other studies, fermentors were used in which methane was supplied with the air.',' In our work on bacteria that utilize gaseous alkenes, the gas is also supplied in the gas phase and the main purpose of the present study was to verify the reliability of the system used for estimation of growth parameters of alkene-utilizing bacteria and to describe, with a model, the biomass productivity of cultures growing at different dilution rates. For this we have used two alkene-utilizing bacteria, a Xanthobacter sp. lo and a Mycobacterium sp." which were grown in chemostat culture on propene and ethene, respectively. MATERIALS AND METHODS ChemicalsEthene and propene were obtained from Hoek Loos (Amsterdam, The Netherlands). All other chemicals were purchased from Janssen Chimica (Beerse, Belgium). The organisms were grown at various dilution rates in mineral salts medium'' with the omission of yeast extract, in l-dm3 working volume fermentors (Applikon, Vlaardingen, The Netherlands). In case of Xanthobacter Py2, the carbon and energy source was propene and for Mycobacterium E3 the carbon and energy source was ethene. These gases were supplied to the culture by passing a mixture of either 2.3% propene or 2.0% ethene in air at a rate of 60 cm3/min through the headspace of the vessel. The flow rates of alkene and air were maintained constant with mass flow meterskontrollers (Brooks type 5850 TR). The gas flow leaving the fermentor was also measured with a mass flowmeter (Brooks type 5850 TR). The alkene concentrations in the gas entering and leaving the vessel were determined by withdrawing samples from Hungate tubes positioned in the inlet and outlet lines, ...
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