The Effect of Ammonia on Morphogenesis in the Acrasieae

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Abstract
In order to study the effect of external conditions on the development of different spp. of Acrasieae. spores were inoculated in the center of a plate prepared by spreading washed Escherichia coli uniformly on non-nutrient agar. The presence of air at humidities ranging from 5% to 95% caused some arrest of development and dwarf forms at the lower humidities, but had no effect on the sorocarps. When Polysphondylium pallidum 15 and Dictyostelium mucoroides 43 were grown in agar slants in which the ratio of dextrose peptone was varied, a ratio of approx. 1:1 for the 2 sugars caused opt. development. P. pallidum was more sensitive to higher concns. of both sugars than D. mucoroides. In order to separate the pH factor from the metabolite effect 5 spp. covering a wide range of types were used on phosphate and phosphate-citrate buffered agars, giving a range in pH from 3.1 to 10.6 in 0.4 unit steps. In the phosphate-citrate system, which was considered more accurate, D. mucoroides and P. violaceum were acid sensitive, whereas all spp. showed normal development at an initial pH of 10.6. Guttulina-like forms appeared with P. pallidum and D. mucoroides with a final pH of 6.85 or above, and above a final pH of 8.5 P. violaceum tended to develop Dictyostelium-like fruits. Neither pH nor peptone per se seemed directly responsible for the Guttulina-like forms, but further tests in which the 3 spp. were exposed to ammonia indicated that free ammonia formed by E. coli in the absence or relative scarcity of dextrose was responsible for morphogenetic suppression or aberrancies. The spp. tested varied in sensitivity to ammonia, which produced a variety of effects ranging from complete inhibition of growth to development of plaques of vegetative amebae or of simple fructifications. CO2 was also found necessary for morphogenetic development.