Acetone-butanol fermentation by Clostridium aurantibutyricum ATCC 17777 from a model medium for palm oil mill effluent

Abstract

Acetone-butanol fermentation by Clostridium aurantibutyricum ATCC 17777 utilizing a model medium for palm oil mill effluent (POME) was investigated. The accumulation of acetone and butanol from glucose by C. aurantibutyricum ATCC 17777 was comparable with that by C. acetobutyricum OUT 8159, which is one of the most potent acetone- and butanol-producing strains. The lipase productivity of C. aurantibutyricum was 15 times higher than that of C. acetobutyricum using the model medium, while fatty acids at a concentration of less than 200 mg/ l stimulated the growth of C. aurantibutyricum in a glucose medium. In batch culture using the model medium for POME at pH 5.5, this strain hydrolysed 28% of the oil and produced 5.4 g/ l of acetone and 1.8 g/ l of butanol. At a higher pH of 6.8, however, the solvent productivities decreased markedly and cells autolysed rapidly after the exhaustion of sugars, though the rate of oil hydrolysis increased up to 46%. Commencing the culture at pH 6.2 and then switching the pH to 5.5, combined with starting glucose feeding during the cultivation, resulted in a reasonable oil hydrolysis rate between those obtained in cultures with constant pHs of 6.2 or 5.5, and higher solvent productivities than in either of the single-pH cultures. Batch culture with glucose feeding and pH switching from 6.8 to 5.5 produced butyrate and acetate instead of the solvents.