Slime Moulds

What is Slime Mould?

Slime moulds or simply slime molds are grouped under fungi earlier, but later, they are kept in the Protista kingdom with other small multicellular and unicellular eukaryotic organisms.

They are the saprophytic type and feed on dead and decaying organic matter.

The name 'slime' is taken from the gelatinous appearance of macroscopic slime moulds. They form aggregates under any unfavourable conditions, and this is common in acellular or plasmodial slime moulds. Their size varies from some centimetres to various square metres.

When there is abundant food, they can live as a single-celled organism, primarily cellular slime moulds.

Slime Moulds Classification

Slime moulds are classified under the Protista kingdom. They resemble fungi and protozoa as well. In modern taxonomy, the true slime moulds fall under Mycetozoa. They are further classified into various classes. The main classes of slime moulds are given below.

  • Dictyostelium - These are cellular slime moulds. They don't form huge coenocytes

  • Myxomycetes - True or acellular slime moulds. They are characterised by plasmodial stage, syncytial (multinucleated).

  • Acrasia- Cellular slime moulds are similar to dictyostelids but have eruptive pseudopodia.

  • Protostele A - Minute, simple, and amoeboid slime moulds.

  • Labyrinthulae - These are the net slime moulds. They form a network of tubes in which amoeba without pseudopodia can swim freely. 

  • Plasmodiophomycetes - These are the parasitic slime molds. These are found as an internal parasite in cabbage roots and cause various diseases in some plants like clubroot disease of cabbage.

  • Fonticula- These are the form volcano-shaped fruiting bodies

Slime moulds are mainly classified as two types. They are Acellular, Cellular slime moulds, where acellular slime moulds are also called Plasmodial slime molds.

Acellular Slime Moulds (Also called Plasmodial)

  • The feeding stage is a multinucleate protoplasm's mass, which is, plasmodium

  • They reproduce asexually when the food is scarce, and moisture is less

  • They can be found creeping as a slimy mass over leaf litter, decaying, and moist logs. It feeds on the dead and decaying microorganisms and organic matter

  • They can grow up to 1 foot in diameter

  • Acellular slime molds examples are, Cribaria, Physarum, Lycogala, Tubifera, Fuligo

The Life Cycle of Acellular Slime Moulds

  • Drying plasmodium forms the stalked fruiting bodies, those bear sporangia

  • Haploid spores are formed in sporangia by meiosis. They also have a thick cell wall and are resistant to adverse conditions extremely

  • These spores germinate to form haploid cells under favourable conditions

  • These haploid cells act as a gamete. Different cell kinds are formed depending on the availability of moisture

  • Biflagellated swarm cells are produced when the conditions are wet. Otherwise, amoeboid myxamoebae are formed. Such cells act as gametes

  • Such haploid gametes fuse to form a diploid zygote

  • Also, the diploid zygote undergoes multiple mitotic division producing multinucleated plasmodium because it doesn't undergo cytoplasmic division (cytokinesis)

Cellular Slime Moulds

  • The feeding stage in a cellular slime moulds is a single-celled amoeboid, which lives as a solitary organism

  • Individual cells feed on the microorganisms and other food matter while creeping on freely swimming or decaying log in freshwater

  • They have a closer resemblance with amoebas

  • Just similar to an amoeba, each cell has a haploid nucleus, and it can divide mitotically

  • When there is a portion of less food, they form aggregate, but retain their individuality because of the thin plasma membrane presence and reproduces asexually by spore formation

  • The chemical then diffuses out and binds to the receptors that present on the surface of the nearby cells by resulting in the movement of cells towards the cAMP (Cyclic Adenosine Monophosphate)

  • When the moisture or food is depleted, they send out a cAMP-mediated chemical signals

  • Cellular slime molds examples are Acytostelium, Dictyostelium, Polysphondylium

The Lifecycle of Cellular Slime Moulds

  • Thousands of cells aggregate, producing a multicellular slug, that creeps for a short distance and settles.

  • Each cell in the slug retains its individuality and its plasma membrane.

  • After settling down, the fruiting bodies are formed in the slug, that contains the spores.

  • Spores are then released and germinate under the favourable conditions into a single haploid amoeboid cell, as the vegetative stage.

  • Spores formation is an asexual method of reproduction.

  • They lack sexual reproduction mostly and also the flagellated gamete stage.

General Slime Molds Characteristics

A few of the general slime molds characteristics are listed below.

  • The slime moulds are creeping on debris, decaying on twigs or leaves, in soil, on tree canopies and moist found on the tree, on the forest floor, and in cold and dark conditions.

  • In the vegetative phase, the protoplast is not surrounded by a cell wall .

  • They lack chlorophyll and saprophytic too. They feed on microorganisms like fungi, bacteria, and yeasts and decompose the dead organic matter.

  • A few of the slime moulds are parasitic and are found in the roots of cabbage and other plants that belong to Brassicaceae family.

  • The plasmodial stage resembles fruiting, and protozoa bodies form spores resembling fungi.

  • Spores have a cell wall, which is made up of cellulose and are resistant to adverse conditions. They can also survive for many years.

FAQs (Frequently Asked Questions)

1. Are Slime Molds Organisms in their Own Right?

There are many slime mold species that are cellular, maintaining their cell integrity throughout development, and others are multinuclear - developing into large single cells with many nuclei.

The cellular slime mould, Dictyostelium discoideum, became an essential model organism studied in great detail by the developmental biologists because it was the fascinating case where an organism starts out as a spore developing into a single amoeboid cell which grows and divides; and then when they are running out of food in the soil, they aggregate into a multicellular slug which differentiates into various cell types and sporulates spores eventually that will spread to other locations. And again, the developmental cycle starts all over. Every slime mould species has its own developmental process in its own right.

2. In What Form is the Food Stored in Slime Molds?

Slime moulds are the unrelated Eukaryotic organisms which can live freely as a single cell but can aggregate to produce the multicellular reproductive structures.

Slime moulds are smaller than a few centimetres, but some species remain up to several square meters and masses up to 30 gm.

Species, which are in the cellular slime mould group, are microscopic on most stages of their life cycle when they exist as haploid, single celled amoebas.

Typically, the amoebas feed on bacteria by engulfing them in a process called phagocytosis when there is a food shortage, the individual haploid amoebas of a cellular slime mould aggregate in a mass of cells known as pseudoplasmodium.

The food can be stored in the form of paramylum (a carbohydrate similar to starch), starch, chrysolaminarin (a storage polysaccharide), fat, and glycogen.