Myxomycetes

MICROBIOLOGY

1. TOPIC Myxomycetes Presented By Samadrita Banik ST. GEORGE COLLEGE M. Sc Microbiology 1 st Semester

2. INTRODUCTION Myxomycetes , is a class of slime molds that contains 5 orders, 14 families, 62 genera and 888 species. They are colloquially known as the plasmodial or a cellular slime moulds.

3. Myxomycetes It is a group of organisms of great scientific interest. Some of these are of remarkable beauty, have delicate structure and brilliant colours . They exist in non-green slimy masses of protoplasm sending out pseudopodia. This has earned for them the name slime molds or slime fungi. They are found in cold, moist shady places in dead organic matter such as decaying logs and fallen dead leaves in the woods. The class includes the true plasmodial acellular slime molds most of which produce pigmented spores in small, delicate sporangia.

4. Characteristics of Myxomycetes The somatic phase is represented by a multinucleate apparently naked acellular slimy protoplasmic mass called the Plasmodium. The Plasmodium is the product of syngamy , hence a diploid structure. The diploid Plasmodium is holocarpic , free living and active. It contains and secretes slime. Normally at the fruiting time, the entire Plasmodium is organised into one or more plant­like reproductive structures, the sporangia ( sporophores ) or under conditions of stress and strains it becomes converted into an irregular hard structure, the sclerotium .

5. Classification of the Myxomycetes ( i ) Ceratiomyxomycetidae : It contains a single order Ceratiomyxales represented by a single family Ceratiomyxaceae . Ceratiomyxa with three exosporous species is the only genus included in this family. (ii) Stemonitomycetidae : It includes a single order Stemonitales which comprises only one family Stemonitaceae . It is endosporous . The somatic phase is of aphano -plasmodium type. (iii) Myxogastromycetidae : It comprises four orders namely Physarales , Siceales , Echinosteliales and Trichiales . All are endosporous . The somatic phase is usually of protoplasmodial or phaneroplasmodial type. The class Myxomycetes thus contains six orders. Of these Physarales belonging to the subclass Myxogastromycetidae is the most important.

6. Features of Myxomycetes The Myxomycota or slime molds, are fungus-like organisms. They are characterised by the absence of cell wall from their amoeboid,’ animal-like vegetative or assimilatory phase . The amoeboid assimilatory phase may consist of a free-living multinucleate mass of protoplasm called a plasmodium or simple uninucleate amoeboid cells, the myxamoebae . Plasmodial slime molds are the true slime molds, pseudoplasmodial slime molds the cellular slime molds and the net plasmodial slime molds are known as the net slime molds . The true slime molds are mostly saprophytic with a few parasitic ones.  The spores escape as biflagellate zoospores which after swimming for some time, lose their flagella become surrounded by delicate envelope and give rise to new net plasmodium.

7. Reproductive Phase of Myxomycetes: Normally on reaching a certain stage of maturity, the Myxomycete Plasmodium passes into the reproductive stage. During this stage the entire Plasmodium becomes converted into one or more fruit-like bodies, the sporophores or spororigia which bear the spores. This process is termed sporulation. With the exception of three species belonging to the order Ceratiomyxales which bear spores externally and are termed exosporous, all other Myxomycetes are endosporous. The latter bear spores within sporophores. The sporophores in the endosporous Myxomycetes chiefly are of three types namely sporangia, aethalia and plasmodiocarps.

8. Sporangia: Most of the endosporous Myxomycetes (order Physarales) produce fruit bodies of this type. At the fruiting time the planeroplasmodium becomes converted into a group of several stalked, sometimes sessile sac-like structures, the sporangia. The sporangia in the group remain separate from one another. Aethalia: Aethalium type of fruit body is characteristic of Lycogala and Fuligo. The Plasmodium, at the fruiting time is fairly large structure. It becomes converted into a group of sac­like sporangia that do not separate from one another.

9. Plasmodiocarp: In forms like Hemitrichia the fruit body is very much like a sessile sporangium that retains the shape of the plasmodial venation. This type of sporophore is called a plasmodiocarp. It is formed by the concentration of the plasmodial protoplasm around some of the main veins followed by the development of peridium around each 

10. Thank You