Abstract
The main bottleneck in the return of industrial butanol production from renewable feedstock through acetone–butanol–ethanol (ABE) fermentation by clostridia, such as Clostridium beijerinckii, is the low final butanol concentration. The problem is caused by the 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 that were obtained after butanol shock and their comparison with data from standard ABE fermentation have resulted in new findings, while confirmed expected population responses. Although butanol shock resulted in upregulation of heat shock protein genes, their regulation is 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 the 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 depend on the concentration of butanol.
Highlights
Clostridia represent ancient, anaerobic, and the first bacteria on Earth able to develop a successful survival strategy (Martin & Sousa, 2016)
The main goal of the study was to capture changes elicited by the addition of approx. 0.5% v/v of butanol to the C. beijerinckii NRRL B-598 culture at the 6th hour of batch fermentation and compare them to data obtained during standard ABE fermentation without interventions
Regarding the physiological state of both cultures at the 6th h, the ratio of viable versus non-viable cells, determined using flow cytometry along with double fluorescent staining with propidium iodide (PI) and carboxyfluorescein diacetate (CFDA), was comparable
Summary
Clostridia represent ancient, anaerobic, and the first bacteria on Earth able to develop a successful survival strategy (Martin & Sousa, 2016). This is exceptional considering all massive extinction events (including the Great Oxygenation Event) in which most of the known species died out. Their fascinating adaptive mechanisms enabling them to cope with hostile environments have not been fully described and understood. The C. beijerinckii species is capable of producing butanol and hydrogen via the acetone–butanol–ethanol (ABE) fermentation pathway, which is the main method for obtaining energy from the bacteria (Lee et al, 2008). Resolving this bottleneck remains an issue to make the technology previously used at the industrial scale more competitive with chemical synthesis (Moon et al, 2016)
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