Water Relations of Salmonella oranienburg; Stimulation of Respiration by Amino Acids

Abstract

The influence of amino-acids on respiration of S. oranienburg was studied over a range of water activity (aw) values. Decrease of the aw value by adding NaCl or sucrose decreased the rate of glucose oxidation and induced a lag. At relatively low values (0-970 aw) but not at high values (0.998 aw), additions of certain amino-acids (proline, aspartic acid, asparagine, glutamic acid, glutamine, cysteine) caused an appreciable synergistic increase in respiration rate. Proline was the most stimulatory amino-acid tested. At 0-960 aw, only proline and its analogue azetidine-2-car-boxylic acid gave appreciable stimulation. These were the only amino-acids which decreased the lag, and lags were not affected by the presence of chloramphenicol. Proline was also stimulatory when glucose was replaced by pyruvate or succinate. The respiration of organisms grown at low aw values was not stimulated by proline unless the organisms were first subjected to osmotic shock. The pro-line effect was also observed with bacteria of four other genera. The data are discussed in relation to the stimulation by proline of bacterial growth at low water activities.