Deeper below the surface – transcriptional changes of selected Clostridium beijerinckii NRRL B-598 genes induced by butanol shock

Abstract

The main bottleneck in the return of industrial butanol production from renewable feedstock, by acetone-butanol-ethanol (ABE) fermentation by clostridia, such as Clostridium beijerinckii, is the low final butanol concentration. The problem is caused by high toxicity of butanol to the production cells, and therefore, understanding the mechanisms by which clostridia react to butanol shock is of key importance. Detailed analyses of transcriptome data obtained after butanol shock, and their comparison with data from standard ABE fermentations resulted in new findings while they confirmed expected population responses as well. Although butanol shock resulted in upregulation of heat shock protein genes, their regulation is probably different than was assumed based on standard ABE fermentation transcriptome data. While glucose uptake, glycolysis and acidogenesis genes were downregulated after butanol shock, solventogenesis genes were upregulated. Cyclopropanation of fatty acids and formation of plasmalogens seem to be significant processes involved in cell membrane stabilization in the presence of butanol. Surprisingly, one of three identified Agr quorum sensing system genes was upregulated. Upregulation of several putative butanol efflux pumps was described after butanol addition and a large putative polyketide gene cluster was found, the transcription of which seemed to be dependent on the concentration of butanol.