Ammonia can stimulate or inhibit aggregate density in Dictyostelium mucoroides: A quantitative test of the hypothesis that ammonia is the aggregation‐suppressing gas

Abstract

Ammonia, at moderate concentrations, stimulates aggregate density of Dictyostelium mucoroides. The range of stimulatory concentrations includes ammonia concentrations established by populations of amebae. At higher concentrations, ammonia inhibits aggregate density. A quantitative test of the hypothesis that ammonia is the aggregation-suppressing gas has been carried out. The concentration of ammonia established over defined populations of amebae is one or two orders of magnitude lower than the concentration of ammonia required to exert the same degree of inhibitory effect as the populations of amebae exert. An additional difference between ammonia and the aggregation-suppressing gas is the fact that increasing concentrations of the aggregation-suppressing gas cause progressively larger aggregation streams, while increasing concentrations of ammonia have no such effect. The stimulatory effect of ammonia at concentrations established by ameba populations indicates that ammonia must be included in the variables affecting the aggregation process and that this ammonia effect must be taken into account in any quantitative modelling of the aggregation process.