Synthesis of Poly--hydroxybutyrate by Agrobacterium radiobacter after Growth on D-Carnitine

Abstract

Agrobacterium radiobacter, isolated from soil, was cultivated on a minimal medium containing different trimethylammonium compounds. In contrast to other bacteria, A.radiobacter is able to utilise D(+)-carnitine, but not the physiologically L(-)-carnitine, as the sole source of carbon and nitrogen. D(+)-Carnitine, which does not exist in nature, is produced as a waste product in chemical procedures for L(-)-carnitine production. During growth on D(+)-carnitine, a NAD + -specific D(+)-carnitine dehydrogenase (specific activity 0.159 U) as an initial enzyme of degradation and poly-β-hydroxybutyrate (PHB) was formed as storage material. The highest PHB content was achieved at growth on a culture medium, which contains 0.5% D(+)-carnitine during the stationary growth phase (60% PHB of cell dry weight). Whereas oxygen limitation has no significant effect on the PHB production, phosphate limitation leads to an increase in PHB formation of up to 71% PHB of cell dry weight after growth on 1% D(+)-carnitine. A.radiobacter seems to be attractive for the conversion of the waste product D(+)-carnitine to PHB valuable as biodegradable and biocompatible plastic.