Survival of Streptococcus lactis in Starvation Conditions

Abstract

The survival characteristics of washed S. lactis ML 3 organisms suspended in phosphate buffer were examined at the growth temperature; Mg2+ markedly prolonged survival. High bacterial concentrations extended survival times because Mg2+ was probably excreted by the bacteria. Surviving organisms in some conditions showed prolonged division lags (especially in the absence of Mg2+). Salt concentration had little effect on survival within wide limits; the optimum pH value for survival was near 7.0. Survival times considerably increased at lower temperatures. Agitation and aeration tended to decrease survival. Death was not influenced by the phase of growth at which cells were harvested from a lactose-limiting medium. Casamino acids markedly increased survival in the presence of Mg2+; arginine was almost as effective as the complete mixture of amino-acids, while other individual amino-acids tested gave only slight increases in survival times. Fermentable carbohydrates accelerated death of starving organisms irrespective of the growth phase from which they were harvested and the limiting nutrient; the accelerated death was reduced by addition of Mg2+.