AbstractsBiology & Animal Science

Pretreatment and hydrolysis of lignocellulosic biomass to fermentable sugars generate a complex mixture of microbial inhibitors such as furan aldehydes (e.g., furfural), which at sublethal concentration in the fermentation medium can be tolerated or detoxified by acetone butanol ethanol (ABE)-producing Clostridium beijerinckii 8052. The response of C. beijerinckii to furfural at the molecular level, however, has not been directly studied. Therefore, this study was to elucidate mechanism employed by C. beijerinckii to detoxify lignocellulose-derived microbial inhibitors and use this information to develop inhibitor-tolerant C. beijerinckii . Towards the long-term goal of developing inhibitor-tolerant Clostridium strains, the first objective was to evaluate ABE fermentation by C. beijerinckii using different proportions of Miscanthus giganteus hydrolysates as carbon source. Compared to the growth of C. beijerinckii in control medium, C. beijerinckii experienced different degrees of inhibition. The degree of inhibition was dose-dependent, and C. beijerinckii did not grow in P2 medium with greater than 25% (v/v) Miscanthus giganteus hydrolysates. To improve tolerance of C. beijerinckii to inhibitors, supplementation of P2 medium with undiluted (100%) Miscanthus giganteus hydrolysates with 4 g/L CaCO3 resulted in successful growth of and ABE production by C. beijerinckii . Spectrophotometric and HPLC analyses revealed that C. beijerinckii transformed lignocellulose-derived furan aldehydes such as furfural and hydroxymethylfurfural to furfuryl alcohol and 2, 5-bis-hydroxymethylfuran, respectively and at a rate of 0.15 and 0.08 g/L/h, respectively.The next study aimed to compare differential gene expressions between C. beijerinckii cultures grown in P2 medium supplemented with and without furfural during acidogenic and solventogenic growth phases. The genomic microarray was used to comprehensively evaluate the inhibitory effects of furfural on C. beijerinckii , and potential adaptation mechanisms to furfural stress. Functional gene group analysis showed that increased expression of genes related to redox balancing may be responsible for the reduction of toxic effects of furfural and alleviation of furfural induced oxidative stress in C. beijerinckii during acidogenic growth phase. However, ABE accumulation, redox balance perturbations, and repression of phosphotransferase system may have caused the termination of the growth of C. beijerinckii following furfural challenge at the solventogenic growth phase. The last objective was to accelerate biotransformation of furfural to furfuryl alcohol by overexpression of furfural-reducting enzymes in C. beijerinckii . Based on results obtained from the transcriptomic analysis of C. beijerinckii , two candidate genes, aldo/keto reductase (AKR) and short-chain dehydrogenase/reductase (SDR) encoded by Cbei_3974 and Cbei_3904 respectively, were…