Slime Mold

Katie Krolick

external image Slime_Mold_On_Deadwood.JPG
Classification/Diagnostic characteristics

There are two different forms of [[#|slime molds]], plasmodial slime mold and cellular slime mold. The plasmodial form of slime mold covers rocks, decaying logs, and other objects as it engulfs bacteria and other food items. Plasmodial slime molds will form if the nucleus of an amoeba begins rapid mitotic division, accompanied by a tremendous increase in cytoplasm and organelles, resulting organism would resemble the multinucleate mass. Whereas the plasmodium is the basic vegetative unit of the plasmodial slime molds, an amoeboid cell is the vegetative unit of the cellular slime molds. (1)Slime molds were once thought to be fungi, but their ability to move and the lack of chitin in their [[#|cell walls]] has caused them to instead be classified as Protoctista.(3). When cellular slime molds are in nutrient-rich soils, they will reproduce quickly. When they need food, they will produce spores that will help them survive in unfavorable conditions. ([[#|Prentice Hall Biology]]). Slime molds are part of the Protista Kingdom, which include eukaryotic, mostly unicellular organisms that generally live in the water. These protistas can be autotrophs or heterotrophs. The slime mold is a heterotroph. (4).
Slime molds formed from the fusion of individual flagellated cells, meaning these cells had flagella organelle. (5).

Relationship to humans:
One of the key characteristics to human decision making is determining how much we value things. The same mechanism of decision making has been found in the slime mold.(6) Seeing as the habitat for slime mold can be in under rocks or logs, or on some damp/wet grass lands, they sometimes overtake small areas of land humans are trying to cultivate. Slime mold is a common contributor to the condition of club root, a condition in which plant roots (mainly those of cabbages, radishes, turnips etc.) are overtaken by slime mold, thus not enabling humans for efficient production of crops.(7).Physarum polycephalum has been proven to be able to solve mazes, mimic man-made transportation networks, and choose the healthiest foods out of a diverse menu, all without a brain or nervous system. These slime molds are challenging what qualifies an organism as intelligent.(8)

Habitat and niche
Plasmodial slime mold covers rocks, decaying logs, and other objects as it engulfs bacteria and food. (1)
Plasmodial slime mold is found in cool, damp, and wet areas. They can grow to become 100 millimeters in diameter and usually are a bright yellow or rusty brown color.(9) Slime mold tends to [[#|avoid]] bright light. This known niche was useful in conducting an experiment with slime mold: areas of bright light were created to mimic physical obstacle in the city of Tokyo on a small scale. Also, pieces of food were placed in the same orientation as major cities and landmarks. Then, slime mold was allowed to grow. The slime mold formed a system of shoots toward the food and avoiding the bright light, and by the end of the experiment, the slime mold resembled the existing rail system in Japan, thanks to the organism's avoidance of bright light. (10)

external image 91918-004-EC45A7B7.jpg
This image of slime mold illustrates how the species resides in moist environments and are very versatile in respect to where they can proliferate. In this picture, the slime mold is growing on a leaf and extends onto a rotting log beneath the leaf. ( [GW]

Predator avoidance

Nutrient acquisition
During the movement of cytoplasmic streaming the organism engulfs bacteria, yeasts, spores of fungi and other small organisms through endocytosis. The cellular slime molds have a lage number of cells called myxamoebas which have single haploid nuclei, and englulf bacteria and other food particles by endocytosis.(1)
When food is abundant, each slime molds cell will live alone, however, when food is in short quantity they will bunch together. They eat wet bark, dead plants and animals, and especially on little organism that live in the soil. (11)
Although slime mold is usually observed moving towards glucose food sources, studies have shown that in enviornments with higher concentrations (10 times as much) of glucose compared to lower, slime mold growth was actually better in the lower concentrated atmosphere (limit on nutrients) (12)

Reproduction and life cycle

Plasmodial slime mold can grow almost indefinitely in its plasmodial stage, as long as the food supple is adequate and other conditions such as moisture and pH, are favorable. The multinucleate mass of plasmodial slime mold is a result from rapid mitotic division of the nucleus of an amoeba. (1)
Cellular slime mold reproduce by mitosis and fission. This simple life cycle stage, consisting of swarms of independent, isolated cells, can persist idefinitely as long as food and moisture are available.(1)

Slime molds form sporangia when conditions become unfavorable. This means that the cells in the mold will change their overall shape to form stalk with fruits than send out out spores. The spores are then picked up by the wind or by passing animals and insects.(12)

Spores from sporangia are dispersed to new habitats, and germinate into small amoebae. This begins the life cycle.(13)

external image slime_mold_lifecycle.gif

Though the types of integument used by protists vary greatly between protists, there are some similarities. For example, all slime molds use cellulose as a form of integument. (14). Also, some slime mold have waxy coverings that are useful for extracting water or helping attract food/nutrients. (evan).(15)

The plasmodial slime mold moves through cytoplasmic streaming where the outer cytoplasmic region of the plasmodium becomes more fluid in places, and cytoplasm moves into those areas, which stretches the plasmodium. When the cyptolasm rushes into a new area and drains away from an older one, the plasmodium is moved over its substrate, and the streaming reverses in its direction. The movement of the streaming results from the microfilaments and a contractile protein called myxomysosin.
When the plasmodial slime mold's fruiting structure dries, it shed its spores. When these spores germinate into wall-less haploid cells, swarm cells, they can live as separate individual cells that move by means of flagella or pseudopods, or they can become walled and resistant resting cysts when conditions are unfavorable. (1)

Sensing environment

A recent study discovered that the slime mold Physarum polycephalum secretes slime as a sort of external spatial memory that enables it to comprehend where it is located in space. Although the slime mold does not possess a brain, spatial memory enhances its ability to navigate in complex environments, allowing it to avoid light and salt, find microbes for food, and determine in what direction movement should occur. By leaving behind a thick mat of nonliving, extracellular slime, the slime mold is able to pinpoint areas it has already foraged in. Since the mold strongly avoids areas covered in its own slime, it uses the slime as a means of remembering where it has already explored. (Alexander Soloviev) (16)

Gas exchange

Waste removal
As slime mold uses enzymes to digest bacteria and other prey, it continuously deposits its waste and moves away from it. Because of its basic function, slime mold does not have a need for a particularly complex mode of waste removal. (2)

Environmental physiology

Internal circulation

Chemical control

Review Questions
1. Why were slime molds thought to be part of the Fungi kingdom and what are the differences between Fungi and slime molds responsible for the change in kingdoms?
2. What do slime molds form, characterized by a cluster of spores, when conditions become unfavorable and eventually disperses to new habitats?
3. What does the slimes primitive spatial memory allow it to do?

(1) Hillis, David, David Sadava, H. Craig Heller, and Mary Price. Principles of Life. High School ed. Sunderland: Sinauer Associates, 2012. Print.
(10) (