Abstract
BackgroundPlant-based cellulose presents the best source of renewable sugars for biofuel production. However, the lignin associated with plant cellulose presents a hurdle as hydrolysis of this component leads to the production of inhibitory compounds, such as ferulic acid.ResultsThe impacts of ferulic acid, a phenolic compound commonly found in lignin hydrolysates, on the growth, solvent production, and transcriptional responses of Clostridium beijerinckii NCIMB 8052 were determined. Addition of ferulic acid to growing cultures resulted in a decrease in the growth and solvent production by 30% and 25%, respectively, when compared to the control cultures. To better understand the toxicity of this compound, microarray analyses were performed using samples taken from these cultures at three different growth states. Several gene ontology terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were identified showing significant change at each status, including ATP-binding cassette (ABC) transporters, two component system, and oxidoreductase activity. Moreover, genes related with efflux systems and heat shock proteins were also strongly up-regulated. Among these, expression of the groESL operon was induced by more than fourfold and was consequently selected to improve C. beijerinckii tolerance to ferulic acid. Real-time quantitative PCR (RT-qPCR) analysis confirmed that C. beijerinckii harboring the plasmid, pSAAT-ptb_Gro, had a two- to fivefold increased groESL operon expression during growth of these cultures. Moreover, this strain was more tolerant to ferulic acid as the growth of this recombinant strain and its bioconversion of glucose into solvents were both improved.ConclusionsUsing transcriptomics, we identified numerous genes that are differentially expressed when C. beijerinckii cultures were exposed to ferulic acid for varying amounts of time. The operon expressing groESL was consistently up-regulated, suggesting that this gene cluster may contribute to strain tolerance. This was confirmed as recombinant cultures showed both an enhanced growth and solvent yield in the presence of 0.5 g/L ferulic acid.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0252-9) contains supplementary material, which is available to authorized users.
Highlights
Plant-based cellulose presents the best source of renewable sugars for biofuel production
C. beijerinckii National Collection of Industrial (NCIMB) 8052 growth and solvent production under ferulic acid stress Ferulic acid was chosen as a model lignocellulosic biomass-derived compound for this study because it has detrimental effects on fermentative microbes even when present at a small concentration [2,3]
The maximum optical density at 600 nm (OD600) for the culture exposed to ferulic acid was 10.4 after 28 h
Summary
Plant-based cellulose presents the best source of renewable sugars for biofuel production. The stress of ferulic acid, one of lignin-derived compounds, was evaluated within Escherichia coli [12] and Lactobacillus brevis [13] Biofuel, such as butanol, was produced using those strains [14,15], they were engineered to have external metabolic pathway and their substrate was limited to glucose, suggesting that non-natural biofuel-producing strains still remains under doubt about their application. It has been shown that furfural and HMF were naturally converted to less toxic alcohol type whereas the phenolic compounds including ferulic acid and syringaldehyde remained within the media [17] Due to these reasons, more studies on the effects of phenolic acid on butanol-producing Clostridium strains has been demanded to develop the new strain tolerant to lignocellulosic biomass hydrolysate
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