Role of amino acids in osmoregulation of non-halophilic bacteria

Abstract

MOST microorganisms show optimal growth at low osmotic pressures, but even so are often able to grow, though more slowly, in the presence of concentrations of environmental solutes sufficiently high to reduce the water activity to values as low as 0.86 (Table 1). The ability of osmophilic yeasts to grow at low water activities depends on the accumulation of high concentrations of polyhydric alcohols inside the cell¹, and similarly, halophilic bacteria accumulate potassium ions². Amino acids, especially proline, have been shown to stimulate growth³ and respiration⁴ of some bacteria at low water activities, and to accumulate in response to increased environmental sodium chloride⁵ and, more particularly, to osmotic dehydration (my unpublished results). I now report that growth of non-halophilic bacteria at low water activities seems to depend on the ability of the cell to balance the environmental osmotic pressure by intracellular accumulation of amino acids, and on the types of amino acid which accumulate.