QUANTITATIVE-ANALYSIS OF GROWTH-STIMULATION BY GLYCINE BETAINE IN SALMONELLA-TYPHIMURIUM

The accumulation of compatible solutes, such as glycine betaine, is kn own to stimulate growth under conditions of osmotic stress. In Salmone lla typhimurium the accumulation of glycine betaine is mediated by two osmotically activated transport systems, prop and ProU. This study wa s undertaken to determine the quantitative relationship between glycin e betaine accumulation from the environment and growth stimulation, an d also the relative roles of the high affinity (ProU) and low affinity (ProP) transport systems. Our data show that relatively low concentra tions of glycine betaine (> 10 mu M) are sufficient to stimulate growt h and that under these conditions prop and ProU transport systems are equivalent. At external concentrations of glycine betaine below 1 mu M , cells able to express the ProU transport system possess a significan t advantage over cells that only possess prop. At high osmolarity the correlation between growth stimulation and cytoplasmic glycine betaine concentration is limited. At low glycine betaine concentrations furth er accumulation of the compatible solute stimulated growth. However, o nce the cells had accumulated 100 nmol glycine betaine per OD650 unit biomass no greater growth stimulation was observed in cells with highe r levels of the compatible solute. The implications of these data for growth and pathogenicity of bacteria in natural ecosystems, such as fo ods, are discussed.