D-BHB belongs to the group of ketone bodies such as acetoacetic acid which are generated in the liver as metabolites of fatty acids. D-BHB made in the liver is converted into acetoacetic acid in the mitochondria and then metabolized through the TCA cycle as an an alternative source of ATP when glucose is deficient. Ketone bodies may accumulate in metabolism during low-carb diets, and ingestion of ketone bodies have been shown to have effects on exercise capacity, prevention of diabetes, anti-aging, etc. Osaka Gas uses Halomonas sp. KM-1 When cultured for 40 hours under aerobic conditions with sugar, sodium glutamate etc., leading to production of PHB. When further cultured for 1 hour under anaerobic conditions, intracellular PHB is converted to D – BHB at concentrations of 90 g/L. Production has been scaled already to about 1 t.
http://www.osakagas.co.jp/en/rd/technical/1266922_6995.html
Osaka Gas news release 2018