Deletion of glyceraldehyde-3-phosphate dehydrogenase (gapN) in Clostridium saccharoperbutylacetonicum N1-4(HMT) using CLEAVE™ increases the ATP pool and accelerates solvent production.

The development and advent of mutagenesis tools for solventogenic clostridial species in recent years has allowed for the increased refinement of industrially relevant strains. In this study we have utilised CLEAVE™, a CRISPR/Cas genome editing system developed by Green Biologics Ltd., to engineer a strain of Clostridium saccharoperbutylacetonicum N1-4(HMT) with potentially useful solvents titres and energy metabolism. As one of two enzymes responsible for the conversion of glyceraldehyde-3-phosphate (GAP) to 3-phosphoglyceric acid in glycolysis, it was hypothesised that deletion of gapN would increase ATP and NADH production that could in turn improve solvent production. Herein, whole genome sequencing has been used to evaluate CLEAVE™ and the successful knockout of gapN, demonstrating a clean knockout with no other detectable variations from the wild type sequence. Elevated solvent levels were detected during the first 24 h of batch fermentation, indicating an earlier shift to solventogenesis. A 2.4-fold increase in ATP concentration was observed, and quantitation of NAD(P)H derivatives revealed a more reducing cytoplasm for the gapN strain. These findings expand our understanding of clostridium carbon metabolism and report a new approach to optimising biofuel production.

The copper-responsive ScsC protein of Salmonella promotes intramacrophage survival and interacts with the arginine sensor ArtI.

The scsABCD (suppressor of copper sensitivity) locus of Salmonella encodes four proteins that resemble the disulfide folding machinery of other bacteria. Previous work has shown that Salmonella encounters toxic levels of copper during infection and the Scs system provides protection against this copper-mediated toxicity. The current work reports that expression of the soluble periplasmic protein StScsC is induced by copper and that intramacrophage survival in the presence of copper is diminished by the loss of StScsC. Using a combination of genetic and proteomic approaches, the abundance of various cysteine-containing periplasmic proteins was found to be elevated by StScsC in the Salmonella periplasm, implicating StScsC in the disulfide folding of superoxide dismutases and proteins involved in amino acid sensing and import. Co-purification and mass spectrometry approaches confirmed that the arginine-sensing periplasmic protein ArtI associates with StScsC via a disulfide interaction, and purified ArtI was shown to alter the thiol redox state of purified StScsC. This work reports the first demonstration of a redox partner for the Scs system of Salmonella and provides insights into how this bacterial pathogen responds to copper stress during infection.