Uptake of choline from salmon flesh and its conversion to glycine betaine in response to salt stress in Shewanella putrefaciens

When cultured in M63 minimal medium plus 0.6 M NaCl, the growth of Shewanel la putrefaciens was strongly inhibited. The addition of an extract from smo ked salmon to this medium restored the growth almost to the unstressed leve l. A comparison of the C-13 NMR spectra of intracellular solutes extracted from S. putrefaciens cells cultured in both conditions revealed the accumul ation of glycine betaine (GB) from the smoked salmon extract (SSE). Analysi s of the osmoprotective properties of this extract for several strains of E scherichia coli (which differ from each other in their ability to accumulat e GB (i) from the surrounding environment, and (ii) from its hydroxylated p recursor choline), demonstrated the absence of GB in the SSE. From the over all results, we inferred that salt-stressed S. putrefaciens cells accumulat ed GB from choline present in the SSE. Furthermore, the use of [C-14]-label ed betaines gave evidence that S. putrefaciens (i) oxidised choline to GB, (ii) accumulated GB as a non-metabolisable osmolyte (up to 1300 nmol (mg dw )(-1) when cultured in a medium containing 0.5 M NaCl and either 1 mM choli ne or 1 mM GB), and (iii) both choline and GB uptake activities were osmoti cally upregulated (both activities were increased more than 50-fold in medi a containing 0.4 to 0.6 M NaCl). In all, our results suggest that in salted smoked salmon, S. putrefaciens imports and oxidises choline, leading to th e intracellular accumulation of GB. (C) 2001 Elsevier Science B.V. All righ ts reserved.