Transcriptome analysis reveals reasons for the low tolerance of Clostridium tyrobutyricum to furan derivatives

Lignocellulosic biomass is considered the most abundant and renewable feedstock for biobased butyric acid production. However, the furan derivatives (FAs, mainly furfural and 5-hydroxymethylfurfural) generated from the pretreatment of lignocellulose severely inhibit the growth of Clostridium tyrobutyricum, which is the best strain for producing butyric acid. The tolerance mechanism of C. tyrobutyricum to FAs has not been investigated thus far. Here, the response of C. tyrobutyricum ATCC 25755 to FA challenge was first evaluated by using comprehensive transcriptional analysis. The results indicated that the genes related to membrane transport, heat shock proteins, and transcriptional regulation were upregulated under FA stress. However, the expression of almost all genes encoding reductases was not changed, and only the ad gene CTK_RS02625 and the bud gene CTK_RS07810 showed a significant increase of 1.05-fold. Then, the enzyme activity assays indicated that BUD could catalyze the reduction of FAs with relatively low activity and that AD could not participate in the conversion of FAs, indicating that the inability to rapidly convert FAs to their low-toxicity alcohols may be the main reason for the low FA tolerance of C. tyrobutyricum. This research provides insights into the development of FA-tolerant strains, thereby enhancing the bioconversion of lignocellulosic biomass to butyric acid.

Automated summary

Lignocellulosic biomass is a rich and renewable feedstock for biobased butyric acid production. However, the presence of furan derivatives from the pretreatment of lignocellulose severely inhibits the growth of the best strain for producing butyric acid, Clostridium tyrobutyricum. This study investigated the tolerance mechanism of C. tyrobutyricum to furan derivatives and found that upregulation of genes related to membrane transport, heat shock proteins, and transcriptional regulation occurs under furan derivative stress. Additionally, it was discovered that C. tyrobutyricum is unable to rapidly convert furan derivatives to low-toxicity alcohols, leading to its low tolerance. These findings provide insights into the development of furan derivative-tolerant strains for enhanced bioconversion of lignocellulosic biomass to butyric acid.