Control of immobilized, non-growing cells for continuous production of metabolites

Summary

A technique for maintaining constant activity during continuous production with immobilized, non-growing cells has been developed. A single stage continuous system with alginate immobilized Clostridium acetobutylicum, was mainly fed with a glucose medium that supported fermentation of acetone-butanol but did not permit microbial growth. The inactivation that occured during these conditions was prevented by pulse-wise addition of nutrients to the reactor.

Using this technique the ratio of biomass to butanol was reduced to 2% (w/w) compared to 34% in a traditional batch culture. At steady state conditions butanol was the major end product with a yield coefficient of 0.20 (g/g glucose). The productivity of butanol was 16.8 g/l·day during these conditions. In a corresponding system with immobilized growing cells the ratio of biomass to butanol was 52–76% and the formation of butyric and acetic acid increased thereby reducing the yield coefficient for butanol to 0.11 (g/g). With the intermittent nutrient dosing technique constant activity from immobilized non-growing cells has been achieved for 8 weeks.