The Relationship Between Cellular Slime Molds and Bacteria in Forest Soil

Abstract

Observations of natural and manipulated populations were used to investigate the regulation of population sizes and community structure in a group of soil amoebae, the cellular slime molds (Dictyosteliida). Correlations of slime mold abundance and distributional patterns with soil bacteria in the field suggest that food supply is a potential factor in the regulation of these species' numbers. One species, Dictyostelium mucoroides, responds most visibly to seasonal changes, spring and fall being peak seasons. When total slime mold number are partitioned into active and encysted forms, amoebae account for as much as 51% and 24% of the population in the fall and spring, respectively, vs. only 10—12% of the population during the summer and winter months. Large additions of various bacteria to field plots caused significant increases in D. mucoroides numbers. Moreover, the ability of this species to respond to a second addition of bacteria, made several days later, depended on its density. High—density populations failed to respond to additional food, whereas those which had already returned to base levels showed increases. These findings support the hypotheses that cellular slime molds are food limited in nature, and that community diversity is due, at least in part, to differential resource utilization by the species in nature.

Do Interactions of Cellular Slime Mold Species Regulate their Densities in Soil?

“…In the field, the CSM respond rapidly to bacterial food supply. For instance, Dictyostelium mucoroides quadrupled its numbers within 1 d after a pulse of Escherichia coli was added (Kuserk 1980). Such direct evidence of resource limitation strengthens the idea that competition is important.…”

“…In our area the four most commonly encountered species are: Dictyostelium mucoroides, Dictyostelium purpureum, Polysphondylium pallidum, and Polysphondylium violaceum. These co-occur on a fine scale, measured in metres (Kuserk 1980), or centimetres (Eisenberg 1976). Two additional species, Dictyostelium discoideum and Dictyostelium minutum, also occur here, but infrequently.…”

“…Two additional species, Dictyostelium discoideum and Dictyostelium minutum, also occur here, but infrequently. Based on previous sampling experience, either Dictyostelium mucoroides or Polysphondylium pallidum is the usual numerical dominant in this area (Eisenberg 1976, Olsen 1978, Kuserk 1980. During active growth the CSM are typical microbes: the single cell (ameba) consumes available resources (soil bacteria) and reproduces by binary fission when it has accumulated sufficient material to become two cells.…”

“…In laboratory cultures the CSM are capable of growth on the same species of bacteria (Anscombe and Singh 1948, Horn 1971, Kuserk 1980). This has suggested to some workers that competition is an important factor in CSM ecology (Horn 1971, Kuserk 1980. In the field, the CSM respond rapidly to bacterial food supply.…”

Advances in Microbial Ecology

“…Stability depended here on the characteristics of the particular species serving as prey, not simply on the diversity of species present. Kuserk (1980) studied. the relationship between cellular slime molds and bacteria in four soils.…”