Spotlight on Spotlight on DictyosteliumDictyosteliumSolitary and Sociable Life Solitary and Sociable Life of a Cellular Slime Mold of a Cellular Slime Mold

Vegetative Cycle Vegetative Cycle • Dictyostelium discoideum, Dictyostelium discoideum, is ais a

species of cellular slime mold species of cellular slime mold included in the Amoebozoan included in the Amoebozoan group of protists. group of protists.

• It spends most of its time in the vegetative state, as an It spends most of its time in the vegetative state, as an individual haploid cell dividing by mitosis to produce new individual haploid cell dividing by mitosis to produce new haploid cells. haploid cells.

• It feeds on bacteria found in the soil or on moist fallen It feeds on bacteria found in the soil or on moist fallen leaves. leaves.

• When the bacterial supply becomes limited, the organism When the bacterial supply becomes limited, the organism transitions either to a social cycle or a sexual cycle.transitions either to a social cycle or a sexual cycle.

Social CycleSocial Cycle• In the social cycle, individual cells aggregate In the social cycle, individual cells aggregate

together, signaling each other through the together, signaling each other through the release of cyclic AMP (cAMP). release of cyclic AMP (cAMP).

• The aggregate becomes a multicellular “slug” The aggregate becomes a multicellular “slug” capable of moving toward light, heat or capable of moving toward light, heat or humidity. humidity.

• The “slug” forms a fruiting body that releases The “slug” forms a fruiting body that releases spores that form new amoeboid cells. spores that form new amoeboid cells.

• Approximately 20% of the cells form the stalk Approximately 20% of the cells form the stalk of the fruiting body, lifting the remaining cells of the fruiting body, lifting the remaining cells to a beneficial place for spore production and to a beneficial place for spore production and dispersal.dispersal.

Social CycleSocial Cycle

Sexual CycleSexual Cycle• For the sexual cycle, single cells aggregate in For the sexual cycle, single cells aggregate in

response to cAMP and sex pheromones.response to cAMP and sex pheromones.• Two cells of opposite mating types fuse, and then Two cells of opposite mating types fuse, and then

begin consuming the other aggregated cells. begin consuming the other aggregated cells. • Before they are consumed, some of the prey cells Before they are consumed, some of the prey cells

form a cellulose wall around the entire group. form a cellulose wall around the entire group. • Elimination of the prey cells leads to a large Elimination of the prey cells leads to a large

diploid cell called a macrocyst.diploid cell called a macrocyst.• The macrocyst undergoes meiosis and releases The macrocyst undergoes meiosis and releases

haploid amoeboid cells.haploid amoeboid cells.

Sexual CycleSexual Cycle

Intersecting Life Cycles of Intersecting Life Cycles of Dictyostelium discoideumDictyostelium discoideum

Questions to AnswerQuestions to Answer

1.1. What type of structure do Amoebozoans like What type of structure do Amoebozoans like “Dicty” use for movement? “Dicty” use for movement?

2.2. What is the usual food source for “Dicty” ?What is the usual food source for “Dicty” ?3.3. Under which environmental conditions does Under which environmental conditions does

the social cycle occur?the social cycle occur?4.4. What chemical signal attracts individual cells What chemical signal attracts individual cells

to aggregate during the social cycle?to aggregate during the social cycle?

Questions to AnswerQuestions to Answer

5.5. What part of the life cycle shows altruism for What part of the life cycle shows altruism for some “Dicty” cells? some “Dicty” cells?

6.6. Which part of the life cycle shows cannibalism Which part of the life cycle shows cannibalism for some “Dicty” cells?for some “Dicty” cells?

7.7. From the fruiting body, are spores produced by From the fruiting body, are spores produced by mitosis or meiosis? mitosis or meiosis?

8.8. From the macrocyst, are spores produced by From the macrocyst, are spores produced by mitosis or meiosis? mitosis or meiosis?