9-34: CLOSTRIDIA TYROBUTYRICUM ADAPTED TO ACETATE FOR THE FERMENTATIONPRODUCTION OF BUTYRATE

Butyric acid, a 4-carbon carboxylic acid, produced by biological conversion of renewable resources has potential applications as a food additive or as a bulk organic commodity chemical. Microorganisms from the genus Clostridium are the most studied in terms of butyric acid fermentation and within this group, the Gram-positive anaerobic spore-former Clostridium tyrobutyricum can produce butyric acid utilizing either glucose or xylose. A source of low-cost xylose feedstock for organic acid fermentation can be obtained from lignocellulosic material by hot water extraction.  However, this auto-hydrolysis of hardwood hemicellulose generates a hydrolyzate with high levels of acetic acid affecting the subsequent fermentation. Previous work using C. tyrobutyricum has shown that 26.3 g/L acetate in the media generates a lag phase of 118 hours before log phase growth and butyric acid production.

As C. tyrobutyricum readily consumes xylose, the development of an acetate tolerant strain has the potential for use in commercial production of butyric acid using hemicellulose derived carbon sources. In this study, a C. tyrobutyricum strain was adapted to 26.3 g/L acetate equivalents in order to examine the effects of this adaptation on the acetate inhibition of xylose fermenting cultures.  Analysis of batch studies found that even in the presence of high levels of inhibitory acetate, tolerant pre-adapted cultures had similar fermentation kinetics as non-inhibited control cultures. Additional insight into the metabolic pathway of xylose consumption and conversion into butyric acid was gained by determining the specific activities of key enzymes in adapted versus control batches.