Process for the biotechnological preparation of poly-d-(-)-3-hydroxybutyric acid

Process for the preparation of poly-(D)-(-)-3-hydroxybutric acid, hereinafter referred to as PHB, which comprises continuously culturing a strain of the microorganism Alcaligenes latus or a PHB-producing mutant derived from this microorganism under aerobic conditions in an aqueous culture medium containing sources of assimilable carbon, nitrogen and phosphorus and the supply of trace nutrients required for the growth of said microorganism with a complete supply of nutrients which is optimum for the growth of the microorganism, under unlimited growth conditions in the temperature range from 36.degree. to 42.degree. in two separate successive fermentation stages comprising a first fermenter and a second fermenter under sterile conditions, the PHB-containing microorganism population cultured in the first fermenter with a dissolved oxygen content of 25 to 50% of the saturation value for air being continuously transferred, together with the culture solution, into the second fermenter in which the culture is continued at a dissolved oxygen content of 8-15% of the saturation value for air, and isolating the PHB by extraction from the biomass thereby obtained.