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Category: Applied and Industrial Microbiology
Molecular Aspects of Butanol Fermentation, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815547/9781555819057_Chap25-1.gif /docserver/preview/fulltext/10.1128/9781555815547/9781555819057_Chap25-2.gifAbstract:
This chapter focuses on the regulation of solvent formation in solventogenic clostridia and in particular in Clostridium acetobutylicum ATCC 824, the most widely studied solventogenic Clostridium at a genetic level, and until recently the only sequenced one. C. beijerinckii and other clostridia are also discussed to the extent that relevant molecular details are known and pertinent to the subject matter. When grown at neutral pH under conditions of high NAD(P)H availability, the culture of C. acetobutylicum is termed alcohologenic as only butanol and ethanol are produced. The chapter focuses on these and related questions with emphasis on more-recent and genomically based work that has not been previously reviewed. The five solventogenic genes on pSOL1 are organized into three operons. Solvent and acid tolerance can be classified as a complex genetic trait, and its characterization requires not only the study of the ''key players'' but also the study of the organism response as a whole. Notable among the methodological improvements in this work were the improved performances of gene inserts from serial enrichment as opposed to a single round of enrichment in batch culture. It seems likely that one or more of the 178 pSOL1 genes is responsible for increased tolerance to butanol. Early attempts relied on the first systematic use of metabolic stoichiometry in order to calculate metabolic fluxes and carry out a large-scale metabolic flux analysis on the overall primary metabolism of C. acetobutylicum.
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Metabolic pathways leading to acid and solvent formation in clostridia. The gene names shown correspond to those in C. acetobutylicum ATCC 824. Genes belonging to the same transcriptional unit share the same background (i.e., shaded or unshaded) on the left-hand table. The two boxes correspond to the genes encoding the proteins shown in the graph. Systematic gene names are shown according to the genome annotation of C. acetobutylicum ATCC 824 ( Nölling et al., 2001 ) whereby CAC is used for genes located on the chromosome and CAP is used for genes located on the pSOL1 megaplasmid.
Schematic depiction of the morphological changes during sporulation and solventogenesis in clostridia. Each stage is named after the equivalent one in B. subtilis, and the main sporulation sigma factors expressed at each stage are also indicated.
Effects of substrates and medium composition on solvent production