Replacing the Calvin cycle with the reductive glycine pathway in Cupriavidus necator.

Formate can be directly produced from CO2 and renewable electricity, making it a promising microbial feedstock for sustainable bioproduction. Cupriavidus necator is one of the few biotechnologically-relevant hosts that can grow on formate, but it uses the Calvin cycle, the high ATP cost of which limits biomass and product yields. Here, we redesign C. necator metabolism for formate assimilation via the synthetic, highly ATP-efficient reductive glycine pathway. First, we demonstrate that the upper pathway segment supports glycine biosynthesis from formate. Next, we explore the endogenous route for glycine assimilation and discover a wasteful oxidation-dependent pathway. By integrating glycine biosynthesis and assimilation we are able to replace C. necator's Calvin cycle with the synthetic pathway and achieve formatotrophic growth. We then engineer more efficient glycine metabolism and use short-term evolution to optimize pathway activity. The final growth yield we achieve (2.6 gCDW/mole-formate) nearly matches that of the WT strain using the Calvin Cycle (2.9 gCDW/mole-formate). We expect that further rational and evolutionary optimization will result in a superior formatotrophic C. necator strain, paving the way towards realizing the formate bio-economy.

Functions of Polycomb Proteins on Active Targets.

Chromatin regulators of the Polycomb group of genes are well-known by their activities as transcriptional repressors. Characteristically, their presence at genomic sites occurs with specific histone modifications and sometimes high-order chromatin structures correlated with silencing of genes involved in cell differentiation. However, evidence gathered in recent years, on flies and mammals, shows that in addition to these sites, Polycomb products bind to a large number of active regulatory regions. Occupied sites include promoters and also intergenic regions, containing enhancers and super-enhancers. Contrasting with occupancies at repressed targets, characteristic histone modifications are low or undetectable. Functions on active targets are dual, restraining gene expression at some targets while promoting activity at others. Our aim here is to summarize the evidence available and discuss the convenience of broadening the scope of research to include Polycomb functions on active targets.