Accumulation of glycinebetaine and its synthesis from radioactive precursors under salt-stress in the cyanobacterium Aphanothece halophytica

Growth in salt-stressed (2.0 M NaCl) Aphanothece halophytica was initially delayed during the first two days of cultivation and eventually attained th e same growth rate as the control (0.5 M NaCl) cells. Glycinebetaine accumu lation increased slightly in control cells but a dramatic increase of glyci nebetaine occurred in salt-stressed cells during a growth period of six day s. There was no apparent increase in the synthesis of [C-14] glycinebetaine in the control cells, in contrast to the marked increase in its synthesis in the salt-stressed cells. Increasing NaCl concentration in the growth med ium induced both the accumulation and the synthesis of glycinebetaine. Time course experiments provided evidence that [C-14] choline was first oxidize d to [C-14] betaine aldehyde which was further oxidized to [C-14] glycinebe taine in A. halophytica. The supporting data for such a pathway were obtain ed from the presence of choline and betaine aldehyde dehydrogenase activiti es found in the membrane and cytoplasmic fractions, respectively. The activ ities of these two enzymes were also enhanced upon increasing NaCl concentr ation in the growth medium from 0.5 M to 2.0 M. Under this condition an inc rease of approximately 1.5-fold was observed for choline dehydrogenase acti vity as compared to 2.5-fold for betaine aldehyde dehydrogenase activity, s uggesting a preferable induction of the latter enzyme by salt stress. A. ha lophytica was able to utilize [C-14] ethanolamine and [C-14] glycine for th e synthesis of [C-14] glycinebetaine.