Abstract
Clostridium beijerinckii NRRL B-598 is a sporulating, butanol and hydrogen producing strain that utilizes carbohydrates by the acetone-butanol-ethanol (ABE) fermentative pathway. The pathway consists of two metabolic phases, acidogenesis and solventogenesis, from which the latter one can be coupled with sporulation. Thorough transcriptomic profiling during a complete life cycle and both metabolic phases completed with flow cytometry, microscopy and a metabolites analysis helped to find out key genes involved in particular cellular events. The description of genes/operons that are closely involved in metabolism or the cell cycle is a necessary condition for metabolic engineering of the strain and will be valuable for all C. beijerinckii strains and other Clostridial species. The study focused on glucose transport and catabolism, hydrogen formation, metabolic stress response, binary fission, motility/chemotaxis and sporulation, which resulted in the composition of the unique image reflecting clostridial population changes. Surprisingly, the main change in expression of individual genes was coupled with the sporulation start and not with the transition from acidogenic to solventogenic metabolism. As expected, solvents formation started at pH decrease and the accumulation of butyric and acetic acids in the cultivation medium.
Highlights
Anaerobic bacteria represent a less well known and studied group compared to their aerobic or facultatively anaerobic counterparts
Samples for the C. beijerinckii NRRL B-598 transcriptomic profiling were taken during batch bioreactor cultivation at time-points T1–T6 to cover the complete cell cycle and both acidogenic and solventogenic phases of ABE fermentation
Prediction of affected operons may not be correct or operons may contain another internal promoter. Such a situation was already described for the strain C. beijerinckii NRRL B-598 in the sigG gene that has its own promoter but is a part of the spoIIG operon[9]
Summary
Anaerobic bacteria represent a less well known and studied group compared to their aerobic or facultatively anaerobic counterparts. The strain shares high homologies of most of the key metabolic and life cycle genes with the strain C. beijerinckii NCIMB 8052, see the comparison of homologies of selected genes[9], there are undeniable differences in the regulation of gene expressions and probably at other regulation levels. These differences are best displayed by comparison of transcriptomic data available for both strains (cf Sedlar et al.[10] and this study for C. beijerinckii NRRL B-598 with Wang et al.[11,12] for C. beijerinckii NCIMB 8052). Major events during the complete life cycle and both metabolic phases were analysed using different methods and compared with expression changes at the single gene or gene cluster levels to obtain further pieces of the mosaic and create a more complete picture of population behaviour in this strain
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