σ54 (σL) plays a central role in carbon metabolism in the industrially relevant Clostridium beijerinckii release_rev_6bc6294a-461b-478c-8622-1fbb18f50b2b

by Rémi Hocq, Maxime Bouilloux-Lafont, Nicolas Lopes Ferreira, François Wasels

Released as a post by Cold Spring Harbor Laboratory.

2018  

Abstract

Microbial production of butanol and isopropanol, two high value-added chemicals, is naturally occurring in the solventogenic <jats:italic>Clostridium beijerinckii</jats:italic> DSM 6423. Despite its ancient discovery, the precise mechanisms controlling alcohol synthesis in this microorganism are poorly understood. In this work, an allyl alcohol tolerant strain obtained by random mutagenesis was characterized. This strain, designated as the AA mutant, shows a dominant production of acids, a severely diminished butanol synthesis capacity, and produces acetone instead of isopropanol. Interestingly, this solvent-deficient strain was also found to have a limited consumption of two carbohydrates and to be still able to form spores, highlighting its particular phenotype. Sequencing of the AA mutant revealed point mutations in several genes including CIBE_0767 (<jats:italic>sigL</jats:italic>), which encodes the σ<jats:sup>54 </jats:sup> sigma factor. Complementation with the wild-type <jats:italic>sigL</jats:italic> gene fully restored solvent production and sugar assimilation, demonstrating that σ<jats:sup>54</jats:sup> plays a central role in regulating these pathways in <jats:italic>C. beijerinckii</jats:italic> DSM 6423. Genomic comparison with other strains further revealed that these functions are probably conserved among the <jats:italic>C. beijerinckii</jats:italic> strains. The importance of σ<jats:sup>54</jats:sup> in <jats:italic>C. beijerinckii</jats:italic> was further assessed by the characterization of a <jats:italic>sigL</jats:italic> deletion mutant of the model strain NCIMB 8052 obtained with a CRISPR/Cas9 tool. The resulting mutant exhibited phenotypic traits similar to the AA strain, and was subsequently complemented with the <jats:italic>sigL</jats:italic> gene from either the wild type or the AA strains. The results of this experiment confirmed the crucial role of σ<jats:sup>54</jats:sup> in the regulation of both solventogenesis and sugar consumption pathways in <jats:italic>C. beijerinckii</jats:italic>.
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Date   2018-12-26
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