Production of poly(D-3-hydroxybutyrate) from CO sub(2), H sub(2), and O sub(2) by high cell density autotrophic cultivation of Alcaligenes eutrophus

Hydrogen-oxidizing bacterium, Alcaligenes eutrophus autotrophically produces biodegradable plastic material, poly(D-3-hydroxybutyrate), P(3HB), from carbon dioxide, hydrogen, and oxygen. In autotrophic cultivation of the microorganism, it is essential to eliminate possible occurrence of gas explosions from the fermentation process. We developed a bench-plant scale, recycled-gas, closed-circuit culture system equipped with several safety features to perform autotrophic cultivation of A. eutrophus by maintaining the oxygen concentration in the substrate gas phase below the lower limit for a gas explosion (6.9%). The culture vessel utilized a basket-type agitator, resulting in a K sub(L)a value of 2970/h. Oxygen gas was also directly fed to the fermentor separately from the other gases. As a result, 91.3 g/dm super(3) of the cells and 61.9 g/dm super(3) of P(3HB) were obtained after 40 h of cultivation under this oxygen-limited condition. The results compared favorably with those reported for mass production of P(3HB) by heterotrophic fermentation.