Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 5, 2013
Publication Date: June 28, 2013
Citation: Liu, S., Bischoff, K.M., Leathers, T.D., Qureshi, N., Rich, J.O., Hughes, S.R. 2013. Butyric acid from anaerobic fermentation of lignocellulosic biomass hydrolysates by Clostridium tyrobutyricum strain RPT-4213. Bioresource Technology. 143(2013):322-329. Interpretive Summary: Butyric acid is a short-chain fatty acid; it has been produced from petroleum and used in animal feeds, perfumes, pharmaceuticals and also a feedstock for plastics, plasticizers, surfactants and textile auxiliaries. We have discovered a new strain of Clostridium sp RPT-4213 that produces butyric acid from anaerobic fermentation. Flask fermentation using MRS media produced 9.47 g L-1 butyric acid from glucose (0.48 g/g glucose). This strain can convert wheat straw (WSH) and switchgrass (SGH) hydrolysate into butyric acid (9.87 g L-1 for WSH and 7.05 g L-1 for SGH). These results can be used to improve the titer and productivity of butyric acid fermentation through process engineering and further scale-up fermentation for profitable production.
Technical Abstract: A newly isolated Clostridium sp. strain RPT-4213 was found to produce butyrate under anaerobic conditions. Fermentations using Lactobacilli MRS Broth produced 9.47 g L-1 butyric acid from glucose (0.48 g/g glucose). However, the strain was not capable of utilizing five carbon sugars. To assess the ability of this strain to convert lignocellulosic materials to butyric acid, biomass feedstocks from agricultural residues including wheat straw, corn fiber, corn stover, and rice hull as well as straw from the energy crop switchgrass were examined in this study. The lignocellulosic materials were pretreated by dilute acid and enzyme hydrolysis to release a majority of the fermentable sugars. Fermentations of wheat straw hydrolysate (WSH), corn fiber hydrolysate (CFH), corn stover hydrolysate (CSH), rice hull hydrolysate (RHH), and switchgrass hydrolysate (SGH) under strict anaerobic conditions indicated that among the conditions tested, 50% WSH with a Clostridia medium (Ct) produced the most butyric acid (8.06 g L-1, 0.46 g/g), followed by 50% SGH with Ct (6.01 g L-1, 0.44 g/g glucose). The data showed that 50% CSH Ct was inhibitory to the fermentation, although 40% CSH Ct yielded 0.43 g/g, suggesting that strain RPT-4213 can tolerate the amount of inhibitors present in 40% CSH. WSH and SGH were then used in pH-controlled bioreactor fermentations using Clostridium sp. RPT-4213 and it was observed that this strain can ferment at least 60% WSH and 60% SGH with a dilute (0.2x) Ct medium. Under these conditions strain RPT-4213 produced 9.87 g L-1 butyric acid in WSH (yield 0.44 g/g) and 7.05 g L-1 butyric acid in SGH (yield 0.42 g/g). These results can be used to further improve the titer and productivity of butyric acid production from pretreated biomass hydrolysates through process engineering.