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Osmoregulation of Brevibaeterium lactofermentum was examined. Exogenous glycine betaine was found to stimulate the growth rate of the bacterium in media of inhibitory osmotic strength. The stimulation was independent of any specific solute, electrolyte, or non-electrolyte. The bacterium did not utilize glycine betaine as a sole carbon source or nitrogen source, or degrade it even in complete medium. The changes in intracellular proline and glycine betaine concentrations were measured in media of different osmolarity. Brevibacterium lactofermentum grown in media without glycine betaine did not accumulate it, but synthesized several hundred millimoles of proline inside the cells. On the other hand, when glycine betaine was added to the growth media, it accumulated in the cell instead of proline. These data indicate that glycine betaine is an osmoprotective c o m p o u n d for B. lactofermentum.

Osmoregulation in Brevibacterium lactofermentum was studied. Proline was accumulated up to approximately 35mg/g dry cell weight in the cells of a wild strain of the bacterium grown under osmotic stress. The osmotic tolerance of a proline auxotroph mutant obtained from the bacterium was lower than that in the wild strain. The activity of pyrroline-5-carboxyIate reductase, one of the enzymes in the proline biosynthetic pathway, increased about 3-fold when the cells of B. lactofermentum were grown under osmotic stress. These data indicated that proline is important in osmoregulation in the bacterium. Under osmotic stress, most bacteria accumulate potassium ions and organic solutes, which are called osmolytes, in their cytoplasm to build up the internal osmotic strength and thereby prevent osmotic dehydration of the cells.1>2) In general, the organic osmolytes used by bacteria are few kinds of organic molecules, for instance, amino acids such as proline and glutamate, sugar, and N-methylated amino acid derivatives.3) Among these organic osmolytes, the functions of proline in enteric

The growth rate, sugar consumption rate, and production rate of an L-lysine producing Brevibacteriurn laetofermentum mutant were stimulated by addition of exogenous glycine betaine. Glycine betaine stimulated the growth rate especially in media of inhibitory osmotic stress, and the stimulation was independent of any specific solute. Therefore growth stimulation by glycine betaine was considered to be an osmoprotective effect. A strong enhancement of the sugar consumption rate and the L-lysine production rate was observed even with resting cells under osmotic stress as well as in a fermentation with growing cells. These data indicated that the osmoprotective effects of glycine betaine on I~-lysine production can be independent of protein synthesis.