Conversion of gamma-butyrobetaine to L-carnitine by Achromobacter cycloclast

L -Carnitine is an ubiquitous substance that plays a major role in the transportation of long-chain fatty acids. We investigated crucial factors that influence microbial conversion of γ-butyrobetaine to L-carnitine using an Achromobacter cycloclast strain. Two-stage culture results showed that γ-butyrobetaine induced enzymes essential for the conversion, which suggests that the precursor should be present in the initial cell growth stage. The addition of yeast extract enhanced L-carnitine production whereas inorganic nitrogen sources inhibited it. Under nitrogen-limiting conditions, the cells accumulated poly-β-hydroxybutyrate instead of L-carnitine. Among the trace elements tested, nickel addition enhanced L-carnitine production by almost twice that of the control and copper strongly inhibited the conversion. L-Carnitine production was reduced when the medium contained inorganic salts of sodium, potassium, and calcium at a concentration greater than 2 g l⁻¹. A higher L-carnitine yield was achieved when cells were incubated in a lower culture volume. The optimal pH for L-carnitine production was 5 to 5.5, whereas that of growth was 7.0, indicating that a pH shift was required. Under optimal conditions, L-carnitine concentrations as high as 15 g l⁻¹ were obtained in 62 h with a 45% molar conversion yield. Journal of Industrial Microbiology & Biotechnology (2001) 26, 309–315. Received 26 November 2000/ Accepted in revised form 27 February 2001