Ethanol production by high performance bacterial fermentation
First Claim
1. A continuous process for producing ethanol by fermentation in an aqueous medium which comprises cultivating Zymomonas mobilis ATCC 29191 in two stages in order to increase ethanol concentration in the fermentation medium, as compared to ethanol concentration in a fermentation medium obtained by continuous cultivation of said Zymomonas mobilis microorganism in a single stage, said process consisting essentially of(i) producing a bacterial biomass comprising a cell suspension of said Zymomonas together with ethanol in an ethanol concentration range which does not substantially inhibit production of said Zymomonas cells in a medium containing glucose and a source of nitrogen;
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wherein in step (i) the source of nitrogen is a mineral salt medium containing NH4 + ions as the sole source or a mineral salt medium containing NH4 + ions supplemented with an organic source of nitrogen,and ethanol reaches a steady state concentration of about 10% w/v in the biomass in (ii).
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Abstract
The present invention is directed to the preparation of ethanol by bacterial fermentation. It makes use of a microorganism capable of producing ethanol and the process is carried out in two stages. In the first stage a bacterial cell suspension is produced together with ethanol in an ethanol concentration range that does not substantially inhibit production of the bacterial cells in a medium containing a source of nitrogen and a source of carbon. Ethanol is then produced in the absence of substantial bacterial cell production by the addition of fermentable sugar to the bacterial cell suspension which is produced in the first stage. The preferred microorganism is a member of the genus Zymomonas.
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10 Claims
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1. A continuous process for producing ethanol by fermentation in an aqueous medium which comprises cultivating Zymomonas mobilis ATCC 29191 in two stages in order to increase ethanol concentration in the fermentation medium, as compared to ethanol concentration in a fermentation medium obtained by continuous cultivation of said Zymomonas mobilis microorganism in a single stage, said process consisting essentially of
(i) producing a bacterial biomass comprising a cell suspension of said Zymomonas together with ethanol in an ethanol concentration range which does not substantially inhibit production of said Zymomonas cells in a medium containing glucose and a source of nitrogen; - and
(ii) producing ethanol in the absence of substantial production of said Zymomonas cells, by the addition of a medium containing glucose to the bacterial cell suspension produced in (i), wherein sugar concentration in stage (ii) does not exceed about 6% w/v; wherein in step (i) the source of nitrogen is a mineral salt medium containing NH4 + ions as the sole source or a mineral salt medium containing NH4 + ions supplemented with an organic source of nitrogen, and ethanol reaches a steady state concentration of about 10% w/v in the biomass in (ii). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification