Continuous production of butanol with immobilized cells ofClostridium acetobutylicum

Spores ofClostridium acetobutylicum were immobilized in calcium alginate. An active gel preparation was obtained after outgrowth of the spores to vegetative cells within the gel matrix. A 100 mL column containing the immobilized cells was used for continuous production. At steady-state conditions the productivity of butanol was 67 g/L reactor volume/day.     

Production of poplar xyloglucan endotransglycosylase using the methylotrophic yeast <Emphasis Type="Italic">Pichia pastoris</Emphasis>

The gene XET16A encoding the enzyme xyloglucan endotransglycosylase (XET) from hybrid aspen (Populus tremula x tremuloides Mich) was transformed into Pichia pastoris GS115 and the enzyme was secreted to the medium. The influence of process conditions on the XET production, activity, and proteolytic degradation were examined. Inactivation of XET occurred in the foam, but could be decreased significantly by using an efficient antifoam. Rich medium (yeast extract plus peptone) was needed for product accumulation, but not for growth. The proteolytic degradation of the enzyme in the medium was substantially decreased by also adding yeast extract and peptone to the glycerol medium before induction with methanol. Decreasing the fermentation pH from 5.0 to 4.0 further reduced the proteolysis. The specific activity was further improved by production at 15 degrees C instead of 22 degrees C. In this way a XET production of 54 mg/L active enzyme could be achieved in the process with a specific activity of 18 Unit/mg protein after a downstream process including centrifugation, micro- and ultrafiltration, and ion exchange chromatography.     

A glucose electrode for fermentation control

An oxygen-stabilized enzyme electrode was applied to monitor the glucose concentration in a fermentor during a batch culture ofCandida utilis. The electrode contains an electrolysis circuit for generation of oxygen within the enzyme layer that keeps the oxygen activity in that layer at the same level as that of the surrounding broth. The electrolysis current is used as a measure of the glucose concentration in the broth. The glucose analysis continued without major disturbances when the dissolved oxygen pressure gradually decreased during the fermentation and also when the broth was subjected to a sudden increase in dissolved oxygen tension. The electrode could also be used in an anaerobic broth. Then the reference electrode was replaced by a constant reference potential that simulated a reference oxygen activity.     

Monitoring glucose consumption in an Escherichia coli cultivation with an enzyme electrode

An autoclavable enzyme electrode, the externally buffered glucose oxidase electrode, is used to monitor the glucose consumption during batch cultivations of E. coli. The electrode signal showed good correlation with data from a conventional procedure and was independent of the dissolved oxygen concentration in the fermentation broth.