Abstract: The present invention relates to a process for the biotechnological preparation of poly-D-(-)-3-hydroxybutyric acid, herein referred to as PHB, which comprises culturing a microorganism that is a strain of Alcaligenes latus or a PHB-producing mutant thereof with unrestricted supply of nutrients, under unlimited growth conditions in the temperature range from 36.degree. to 42.degree. C. at a dissolved oxygen content of 25 to 50% of the saturation value for air and a pH value of 6.0 to 7.5. The PHB is then isolated in the customary manner from the biomass thereby obtained.

Abstract: The present invention relates to a process for the biotechnological preparation of poly-D-(-)-3-hydroxybutyric acid (PHB) which comprises continuously culturing a microorganism that is a strain of Alcaligenes latus or a PHB-producing mutant thereof, in two separate successive fermentation stages with unrestricted supply of nutrients. The PHB-containing microorganism population cultured in the first stage with a dissolved oxygen content of 25 to 50% of the saturation value for air is then continuously transferred into a second fermentation stage in which the culture is continued at a dissolved oxygen content of 8-15% of the saturation value of air. The PHB is extracted in the usual manner from the biomass thereby obtained.