[R.J.MIitchell]Analysis of Clostridium beijerinckii NCIMB 8052’s Transcriptional Response to Ferulic Acid and Its Application to Enhance the Strain Tolerance

Prof. Robert J. Mitchell recently had a paper accepted to Biotechnology for Biofuels (IF 6.221 and Top 7% journal)

The title and abstract are below.

A brief synopsis of the paper:

Prof. Mitchell's team used transcriptomics, a method to determine how an organism responds to its environment, to identify responses from bioenergy-producing bacteria when exposed to plant hydrolysates. These hydrolysates are important since they contain many fermentable sugars that can be used to produce biofuels. However they contain some toxic compounds as well. We found that by slightly changing the bacteria based upon their transcriptomic responses that they are more resistant to the toxic chemicals found in plant hydrolysates leading to improved biofuel productions and yields.


Title: Analysis of Clostridium beijerinckii NCIMB 8052’s Transcriptional Response to Ferulic Acid and Its Application to Enhance the Strain Tolerance

Authors: Siseon Lee Jin Hyung Lee and Robert J. Mitchell

Abstract:

Background

Plant-based cellulose presents the best source of renewable sugars for biofuels 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.

Results

The impacts of ferulic acid, a phenolic compound commonly found in lignin hydrolysates, on the growth, solvent production and transcriptional responses of C. 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 KEGG pathways were identified showing significant change at each status, including 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 4-fold and was consequently selected to improve C. beijerinckii tolerance to ferulic acid. RT-qPCR analysis confirmed that C. beijerinckii harbouring the plasmid, pSAAT-ptb_Gro, had a 2- to 5-fold 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.

Conclusions

Using 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.