Dictyostelium discoideum is a eukaryotic microbe that lives a unique lifestyle that involves changing from a unicellular to multicellular organism. Recent studies have shown that not only is it unique in this aspect, but it is unique in that it actually cultivates its own food supply, being dubbed the world’s “smallest farmer” amongst microbiologists. This article is based on a recent study led by Debra Brock at the Washington Universty of St. Louis.
Dictyostelium discoideum is a heterotrophic, soil-living amoeba, and it’s unique in the fact that is starts out as a unicellular organism, but becomes a multicellular organism later in life. This occurs when its unicellular pieces come together to from a slug that can move around in the soil. But it’s not just unique in this aspect. It is also a rare species because it has been proven to carry its bacterial prey around with it and essentially “farm” it for a larger food supply
In 2011, these characteristics of D. discoideum were observed and recorded, but recent discoveries made by Debra Brock of Washington University in St. Louis show that this process is more complex than originally thought. It turns out that the bacterial prey of D. discoideum is actually found in two forms – an edible form and an inedible, toxic form. The bacterial prey is called Pseudomonas fluorescens.
The toxic form of P. fluorescens is a result of a mutation that affects the controls of two toxic chemicals, called chromene and pyrrolnitrin. These chemicals are believed to inhibit sporulation, which is an important step in the amoeba’s life cycle.
Although the toxic form can kill D. dictyostelium, D. dictylostelium still carries both lineages in order to increase its food supply. This is actually statistically favorable because the toxic form of the bacterial prey only occurs about 10% of the time. It is believed that the original form of P. fluorescens is actually the inedible form, but it has evolved into the edible form in order to be picked up by the amoeba and to be transported to different areas in the environment with differing nutrient levels. This evolution is actually beneficial to the prey bacteria because it has a greater chance of survival if it can spread its population out. In turn, the amoeba allows its prey to grow in the new environment and can cultivate them for its own food supply.
This is a brand new discovery that allows a glimpse into mutualism, evolution, and altruism at the microbial level.