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A simple fed-batch system which controls substrate feeding by measuring the CO, produced during the fermentation, was developped. This Fed-batch approach allowed high production of 1,3-propanediol from glycerol by Clostridium butyricum by avoiding substrate inhibition phenomena. 65 g/l of 1,3-propanediol was produced with a productivity of 1.21 g/l.h and a yield of 0.56. The concentration of 1,3-propanediol obtained and the productivity were significantly higher than those reached in batch culture.

The effects of nitrogen (N), phosphorus (P), zinc (Zn) or iron (Fe) limitations on lipid and especially a-linolenic acid (ALA) synthesis in the oleaginous yeast Rhodotorula glutinis have been investigated. Exhaustion of the limiting element in the medium resulted in an enhancement of both the fatty acid cell content (FA/X) and the corresponding productivity. Except for Fe-limited media, lipid accumulation was always coupled with an increase in the yield of ALA synthesis, whereas in all the limiting conditions the productivity of ALA declined. Kinetic investigations showed that this decline resulted from a sharp decrease in the specific rates of ALA synthesis associated with slowing down of growth. A comparative study showed that the highest yields and specific rates of fatty acid and ALA synthesis were induced by P-limitation early in the lipid accumulation phase. However, above a F A / X of 15%, N-limiting conditions become more attractive for producing lipids. During P-limited growth a down-shift of temperature from 30°C to 25°C was shown to reduce the range of F A / X values at which the specific rate of fatty acid synthesis was maximal but without any other effect on fatty acid formation. In contrast, the decreased temperature resulted in enhanced ALA production by maintaining the specific rate of synthesis near to the maximal value of 3.6 mg gx2 h -t, where X* is free fatty acid biomass, and increased the corresponding yield by a factor of up to three.

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