Time-course transcriptome of Bacillus coagulans in the presence of 1-ethyl-3-methylimidazolium acetate

Ionic liquids are promising compounds for use in production of biorenewable fuels and chemicals because of their ability to disrupt and fractionate (i.e., pretreat) lignocellulosic feedstocks for enhanced enzymatic digestibility. An ionic liquid that has received considerable attention for its effectiveness in pretreating lignocellulosic biomass is 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). However, residual [C2mim][OAc] left unrecovered post-pretreatment can inhibit microorganisms and enzymes used downstream. A strain of Bacillus coagulans isolated from a thermophilic microbial community grown in the presence of [C2mim][OAc] exhibits tolerance to industrially relevant levels of [C2mim][OAc] and therefore presents a model bacterium for better understanding bacterial tolerance to these ionic liquids. To characterize growth kinetics in the presence of [C2mim][OAc], liquid cultures of B. coagulans were grown at 55˚C in MI media with and without 2%[C2mim][OAc]. While [C2mim][OAc] did not prevent growth at this level, significant increases in lag times were observed. mRNA were isolated from these cultures and corresponding cDNA were sequenced using the Illumina HiSeq platform. Transcriptomic data was then analyzed to identify genes with differential expression in the presence of [C2mim][OAc]. 130 genes were discovered to be upregulated in cells exposed to ionic liquid, with a major number of these genes relating to iron cationic transporters. Further investigation of these genes may provide tolerance mechanisms that may be engineered into more industrially relevant organisms to confer ionic liquid tolerance during biofuel production.