Acetogenic mixotrophy for carbon-neutral and carbon-negative production of chemicals.

Microbial conversion of renewable carbon sources into valuable chemicals can significantly reduce our reliance on fossil resources and decrease the carbon footprint of chemical manufacturing. Of emerging interest is anaerobic, nonphotosynthetic mixotrophy (ANP mixotrophy) that simultaneously converts renewable carbohydrates and C1 gases (CO2 and CO) into value-added chemical products in carbon-neutral and even carbon-negative fermentations. Despite significant advances in ANP mixotrophy over the past decade, several challenges remain. We discuss key challenges for carbon-neutral/negative ANP fermentations, notably the necessity of supplying additional electrons for reduced metabolite production, the slow adoption of genetic tools, uncertainties about carbon catabolite repression, and gas transfer limitations.