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

L-Carnitine is an ubiquitous substance that plays a major role in the trans portation of long-chain fatty acids. We investigated crucial factors that i nfluence microbial conversion of gamma -butyrobetaine to L-carnitine using an Achromobacter cycloclast strain. Two-stage culture results showed that g amma -butyrobetaine induced enzymes essential for the conversion, which sug gests that the precursor should be present in the initial cell growth stage . The addition of yeast extract enhanced L-carnitine production whereas ino rganic nitrogen sources inhibited it. Under nitrogen-limiting conditions, t he cells accumulated poly-beta -hydroxybutyrate instead of L-carnitine. Amo ng the trace elements tested, nickel addition enhanced L-carnitine producti on by almost twice that of the control and copper strongly inhibited the co nversion. L-Carnitine production was reduced when the medium contained inor ganic salts of sodium, potassium, and calcium at a concentration greater th an 2 g l(-1). A higher L-carnitine yield was achieved when cells were incub ated in a lower culture volume. The optimal pH for L-carnitine production w as 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.