or completely absent. However, knallgas bacteria, when growing as chemolithoautotrophs, can integrate a molecule of CO2 to produce, through the Calvin–Benson cycle, biomolecules necessary for the cell: 6H2 + 2O2 + CO2 (CH2O) + 5H2O A study of Alcaligenes eutropha, a representative knallgas bacterium, found that at low concentrations of O2 (about 10 mol %) and consequently with a low ΔH2/ΔCO2 molar ratio (3.3), the energy efficiency of CO2 fixation increases to 50%. Once assimilated, some of the carbon may be stored as polyhydroxybutyrate. Uses Given enough nutrients, H2, O2 and CO2, many knallgas bacteria can be grown quickly in vats using only a small amount of land area. This makes it possible to cultivate them as an environmentally sustainable source of food and other products. For example, the polyhydroxybutyrate the bacteria produce can be used as a feedstock to produce biodegradable plastics in various eco-sustainable applications. Solar Foods is a startup that has sought to commercialize knallgas bacteria for food production, using renewable energy to split hydrogen to grow a neutral-tasting, protein-rich food source for use in products such as artificial meat. Research studies have suggested that knallgas cultivation is more environmentally friendly than traditional agriculture. References Bacteria Hydrogen Lithotrophs