We've Been Slimed

Several bright red plasmodia of Raspberry Slime Mold
(Tubifera ferruginosa) on a log.  Rowan County, NC.

This spring was cool and wet, the perfect weather for slime molds.  These amazing creatures are not really Fungi as the mold in their name suggests, but are classified with amoebas.  Slime molds all have an amoeba stage in their life cycles.  There are several groups of microbes that are called slime molds.  The ones we have seen this spring are all giant amoebas.  These monstrous cells, called plasmodia, and can be several inches across.  Plasmodia are often brightly colored and they contain millions of nuclei.  These huge cells crawl across leaf litter or rotting logs and engulf any microorganism in their path.  Eventually the plasmodium produces fruiting bodies that release spores.  These reproductive cells float on the breeze and germinate into new amoebas that then grow into new plasmodia.  Slime molds were the inspiration for the classic 1950s sci fi movie, The Blob.  In this film, a giant plasmodium oozes around a Pennsylvania town consuming the citizenry. 

Close up of Raspberry slime mold showing the red
bumps that resemble a raspberry fruit. Rowan County, NC.

On a drizzly day in May, we were hiking through the woods in a local park.  As we rounded a curve in the trail, we saw brilliant red slime molds on the trunk of a downed tree.  This was a group plasmodia of the Raspberry Slime Molds (Tubifera ferruginosa).   The plasmodia had many small red bumps that mimic the compound fruits of raspberry.  The Raspberry Slime Mold was getting ready to make spores. When we returned two days later, the spore producing sporangia were mature and had turned dark brown. 

Raspberry Slime Mold with white stalks supporting
the developing sporgangia. Rowan County, NC. 

Raspberry Slime mold as the sporangia develop.
Rowan County, NC.

Raspberry Slime Mold with mature, brown sporangia. 
These structures were releasing spores. Rowan County, NC.

Another slime mold we found this spring was a bright white one, Ceratiomyxa fruticulosa, the Coral Slime Mold.  This slime mold was also growing on a log and the delicate, branched white fruiting bodies stood out against the black of the log. 

White plasmodia of Coral Slime Mold (Ceratiomyxa fruticulosa)
on a decaying log. Rowan County, NC. 

Closeup of of Coral Slime Mold plasmodia.
Rowan County, NC. 

Near the Coral Slime Mold, we found another interesting one, Arcyria cinerea.  This slime mold is one of the most common on rotting logs but does not have a common name.   Arcyria cinerea makes delicate, cylindrical, gray sporangia. 

Sporangia of Arcyria cinerea.  Rowan County. NC.

Physarum polycephalum lives in leaf litter or on rotten logs.  This common slime mold is bright yellow and the plasmodium can be a foot across.   Physarum polycephalum is the lab rat of slime molds because its large cell size makes it important in the study cell movement. 

Giant plasmodium of Physarum polycephalum.  Rowan County, NC.

This spring we also saw a beautiful yellow slime mold with an unappealing name, Dog Vomit Slime Mold (Fuligo septica).  The large, bright yellow plasmodium gives this organism another common name, Scrambled Egg Slime.   Dog Vomit Slime Mold often appears on wood chip mulch but may also show up on dead wood of many types.  Dog Vomit Slime Mold has the curious ability to concentrate the metal zinc in its plasmodium.  Russian researchers found Fuligo septica plasmodia contain more than 20 times the environmental concentration of zinc.  The reason for this hyper-accumulation of a toxic metal is unknown, but the yellow pigment of the slime mold helps sequester the zinc and make it less toxic. After crawling around consuming other microbes, the bright yellow plasmodium turns brown and produces spores.  This spore generating stage really does look like dog vomit. 

A migrating plasmodium of Dog Vomit Slime Mold (Fuligo septica).
Rowan County, NC.

Dog Vomit Slime Mold releasing spores.
Rowan County, NC. 

Leaf litter, soil and rotting logs are the natural habitat of countless protozoa, bacteria, fungi and algae.  This biodiversity is mostly invisible to us, but in the case of slime molds their giant cells let us get a glimpse of this world.