Riboflavin synthesis from gaseous nitrogen and carbon dioxide by a hybrid inorganic-biological system.

Abstract

Microbes can provide a more sustainable and energy-efficient method of food and nutrient production compared to plant and animal sources, but energy-intensive carbon (e.g., sugars) and nitrogen (e.g., ammonia) inputs are required. Gas-fixing microorganisms that can grow on H₂ from renewable water splitting and gaseous CO₂ and N₂ offer a renewable path to overcoming these limitations but confront challenges owing to the scarcity of genetic engineering in such organisms. Here, we demonstrate that the hydrogen-oxidizing carbon- and nitrogen-fixing microorganism <i>Xanthobacter autotrophicus</i> grown on a CO₂/N₂/H₂ gas mixture can overproduce the vitamin riboflavin (vitamin B₂). We identify plasmids and promoters for use in this bacterium and employ a constitutive promoter to overexpress riboflavin pathway enzymes. Riboflavin production is quantified at 15 times that of the wild-type organism. We demonstrate that riboflavin overproduction is maintained when the bacterium is grown under hybrid inorganic-biological conditions, in which H₂ from water splitting, along with CO₂ and N₂, is fed to the bacterium, establishing the viability of the approach to sustainably produce food and nutrients.