Acetone-butanol fermentation revisited.

WhenClostridium acetobutylicum was grown in batch culture under iron limitation (0.2 mg·l−1) at a pH of 4.8, glucose was fermented, to butanol as the major fermentation end product, and small quantities of acetic acid were produced. The final conversion yield of glucose into butanol could be increased from 20% to 30% by iron limitation. The acetonebutanol ratio was changed from 3.7 (control) to 11.8. Hydrogenase specific activity was decreased by 40% and acetoacetate decarboxylase specific activity by 25% under iron limitation. Thus, iron limitation affects carbon and electron flow in addition to hydrogenase.

Iron effect on acetone-butanol fermentation

Serial enrichment was used to obtain a strain ofClostridium acetobutylicum demonstrating a 40% increase in tolerance to added butanol and a further 17% improvement in the ability to produce butanol. The glucose and the butyrate consumption were higher for the G1 variant than for the wild-type strain. In consideration of the higher butanol tolerance, a disappointly low titer of butanol was produced by the new strain. This can be explained by the higher level of autobacteriocin produced by G1. Control of autobacteriocin production appears to be one of the key factors limiting the potential of the acetone butanol fermentation.

Butanol tolerance and autobacteriocin production byClostridium acetobutylicum

Cet article de synthese aborde les points suivants: interet industriel de la production de solvants par fermentation et realisations actuelles, description des microorganismes utilises et des voies metaboliques conduisant a la production de solvants (fermentations ethanolique et acetonobutylique, production d'isopropanol, production d'acetone plus ethanol, production de butanediol), etude de l'inhibition par les produits de fermentation, aspects technologiques (pretraitement des substrats, conception et conditions de fonctionnement des bioreacteurs, techniques de recuperation des produits de fermentation, contraintes et ameliorations possibles des procedes), perspectives

Solvent production by microorganisms

Effects of butyric and acetic acids on acetone-butanol formation by Clostridium acetobutylicum

The production of acetone by Clostridium acetobutylicum was favoured when acetate was added to the culture medium. In the presence of acetate an increase of the acetone concentration from 4.2 to 10.1 g per liter was noted without any change of the butanol concentration. The coenzyme A transferase and the acetoacetate carboxylase were not limiting factors since the addition of acetic acid allowed the biosynthesis of acetone to increase. The control of acetate production by the cells, which is not coupled to the butanol formation, is the key point of the acetone biosynthesis.

H. Petitdemange

Papers

Mechanism of the acetone formation by Clostridium acetobutylicum