Zygomycotina

Zygomycotina- General account with examples.

1. Zygomycotina Vaishali S.Patil Professor, Department of Botany Shri Shivaji College of Arts, Commerce & Science Akola

2. The fungi belonging to this group are generally terrestrial and they produce zygospore (Gr. zygos — yoke; Spora — seed, spore) after sexual reproduction. The thallus is normally haploid, consisting of coenocytic mycelium and its cell wall contains chitin and chitosan . The mycelium contains cell organelles like other fungi, except typical golgi bodies and centriole . Asexual reproduction takes place by aplanospores . Sexual reproduction takes place by gametangial copulation, resulting in the formation of zygospore .

3. Subdivision Zygomycotina divided into two classes: i . Zygomycetes -The Zygomycetes division of fungi includes mostly terrestrial fungi. Because the hyphae have no cross walls between the cells, they are said to be  coenocytic .  Sexual reproduction in these organisms occurs when sexually opposite hyphae fuse and form spores called  zygospores . A common member is the bread mold   Rhizopus stolonifer .  This fungus forms a white or gray mycelium on bread. The sporangia containing the asexual spores can be seen extending into the air. One species of  Rhizopus  is used to ferment rice to make sake, and another species is used in the production of cortisone. ii. Trichomycetes -They are obligate symbiotic organisms that typically live in the guts of arthropods. They are generally viewed as commensals , having little effect on the host, but in stressful environments they might confer an advantage to colonized hosts; in some cases they act as pathogens. Most trichomycetes colonize freshwater and marine arthropods, but some colonize terrestrial arthropods. Hosts are filter feeders, detritus feeders, or aquatic grazers, but not predators or fluid feeders (e.g., Brachycera ).

4. Mucor (“Black or Bread mould” mould) Kingdom: Mycota Division: Zygomycota Sub-division: Zygomycotina Class: Zygomycetes Order: Mucorales Family: Mucoraceae Genus: Mucor Characters- There are many species of Mucor (around 50) that are distributed worldwide. It can cause diseases particularly called mucormycosis that might affect the mucous membrane, lungs, eyes, skin etc. 

5. The hyphae are coenocytic , but septa may appear in the mature hyphae . The cytoplasm of the hypha appears granular. It lives in a habitat like organic soil, bread, jam, jellies, a dead decaying matter of fruits, vegetables and plants i.e. “ Saprophytic ” and “ Coprophilous ” (grows in cow dung or the dung of other herbivorous animals). The vegetative body of is “ Eucarpic ” ( Thallus is differentiated into vegetative and reproductive structure) The major reserve food material is in the form of glycogen and oil droplets. The cell is composed of mainly cellulose and chitin.

6. Structure- The mycelium is highly branched, multinucleate and it forms a fine network of hyphae . It is filamentous, aseptate or coenocytic . Colony is white to grey and turns to brown Sporangiophore is elongated, slightly narrow in shape. Sporangiophore swells up to form a dome-like structure called “ Columella .”  Sporangium is the round and thick outer covering which carries numerous spores inside it. It can be globose to spherical. Spores are the reproductive structures forms within the sporangium which are simple, black, motile or non-motile, flattened and variable in shape and size.

7. Reproduction: 1.Vegetative reproduction- It occurs by the fragmentation method, where a vegetative cell breaks into several fragments during some unfavourable conditions. After which, each fragment then develops into a new vegetative body. 2.Asexual reproduction- It occurs through the asexual and non-motile spores like: a) Chlamydospores -A hard wall covers these spores, and it develops inside the vegetative cell during unfavourable conditions. In unfavourable conditions, mycelium becomes septate by the

8. accumulation of nuclei and cytoplasm in a certain portion and becomes surrounded by a thick wall called chlamydospores . This spore then detaches from the mycelium and remains dormant. On favourable conditions, they form a germ tube. b) Oidiospores -When a mycelium grows in a substrate (rich in sugar), some small, thin-walled and pearl-like reproductive structures form that detaches out of the vegetative cell as in budding of yeast. Then oidospores remain dormant for some time and on favourable conditions, it forms a germination tube to form a new vegetative body.

9. c) Sporangiospores - These are the spores that form within the cell or sporangium and are non-motile. From the hyphae , first  sporangiophores  arise singly that are erect in position and unbranched . After maturation it develops a large round  sporangium and inner columella . Inside the wall of sporangium many thin-walled, multinucleate spores called “ Sporangiospores ” are developed. The sporangiospores then releases out of the sporangia after the columnella swells up due to the pressure exerted on the sporangial wall. As a result,  cell lysis   occurs. The spores remain dormant for some time, and when they obtain suitable substratum, they germinate to a new vegetative body through the germ tube.

10. Sexual reproduction-

11. First, the thallus of two opposite strains, i.e. one is (+), and other is (-), comes in contact with each other. When they come in contact, there develops a small outgrowth or protuberance from both of the thalli . After that, the outgrowth swells to form “ Progametangium ”. Then septum develops between the progametangium , and the fusion of progametangia occurs that results in the formation of gametes called “ Coenogametes ”. Then gametes of both the strains fuse to form a “ Zygote ”. The zygote then enlarges in size and get surrounded by a thick-walled structure called “ Zygospore ”. Zygospore is dark black in colour, which gets covered by the two layers, namely: Outer layer: Also called  Exosporium . Inner layer: Also called  Endosporium . The zygospore remains dormant for some time and on favourable conditions, promycelium develops out from the zygospore , forming a new vegetative body.

12. Economic Importance – Some members of the Mucorales are commonly used to ferment foods. The fermentation of foods is nutritionally important because the fungi contribute substantially to the nutritional value of the foods. • It produce important industrial products such as lactic acid, amylases, rennin and organic such as fumaric acid. Other species are used in industrial fermentations in the conversion of starch into sugar. • The preparation of Chinese cheese called sufu from soybeans with the help of the mucor Actinomucor . • Many diseases of fruits that occur during storage and transit are caused by the Mucorales . • Some species of Mucor attack stored grains. • Some species of Mucorales are known to cause the fatal diseases called Mucoromycosis in domesticated animals and man. This infects lungs, brainand other organs, particularly in man .

13. Rhizopus -(The Bread Mould) Kingdom-Fungi Division- Zygomycota Class- Zygomycetes Order- Mucorales Family- Mucoraceae Genus- Rhizopus   It is a saprophytic and parasitic fungi, found in moist or damp places,vegetables , fruits, bread, jellies, etc. The vegetative structure is made up of coenocytic (multinucleated) and branched hyphae . 

14. They are fast-growing fungi and have a cottony appearance The body consists of branched mycelium. The mycelium is  coenocytic  and composed of three types of hyphae ; stolon , rhizoids and sporangiophores Stolon   is the internodal region, it is aerial, forms an arch and touches the substratum forming nodal region Rhizoids  are formed where the stolon touches the substratum at nodes. They are branched, anchor the mycelium to the substratum and absorb food. Sporangiophores   are the aerial and reproductive mycelia. They are branched and consist of sporangiospores terminally. The cell wall is made up of chitin. The cytoplasm is multinucleated and consists of other cell organelles such as mitochondria, endoplasmic reticulum, Golgi bodies, vacuoles and oil droplets.

15. Reproduction - By vegetative, asexual and sexual methods. Vegetative reproduction   is by fragmentation and each of the fragments of a stolon develops separately making a complete mycelium Asexual reproduction   is by the formation of chlamydospores and sporangiospores . Formation of Chlamydospores :  Chlamydospores are formed during unfavourable conditions. An intercalary segment of mycelium develops due to the formation of septae and

16. Formation of Sporangiospores :   Sporangiospores are formed terminally in sporangia of aerial mycelium called sporangiophores . They are formed under favourable conditions.It develop from the upper side of the rhizoidal node.The apical part swells up forming sporangium, as nuclei and cytoplasm move apically.The cytoplasm of sporangium differentiates into the denser peripheral region with more nuclei and the central columella region with fewer nuclei and more vacuoles.Sporangiospores develop inside sporangium. They are multinucleated and non-motile The wall of sporangium ruptures after maturation and sporangiospores come out as a powdery mass.After getting suitable condition and substratum, each spore germinates into a new mycelium. accumulation of protoplasm. It is thick-walled and detaches from the mycelium once it dries. They remain dormant until the favourable conditions return and then germinate to form a new mycelium

17. Sexual reproduction   is by fusion of two compatible hyphae . The species are heterothallic, i.e. having different mycelium for + and – mating strains or homothallic.The compatible hyphae come together. In both the mycelia, a small outgrowth develops. It is known as progametangia Nuclei and cytoplasm move towards the apical region and progametangia make contact.The apical region is separated from the rest of the hyphae by septae formation. This is known as gametangia.Gametangia conjugate to form a multinucleated structure. Plasmogamy is followed by karyogamy and diploid (2n) zygote is formed. It is known as  zygospore .  Rest of the unpaired nuclei degenerate. Zygospores enlarge and become thick-walled and resistant to adverse environmental conditions. On getting favourable conditions, zygospores germinate. The inner wall of zygospore develops into promycelium forming germ sporangiophore , with germ, sporangium formed apically. Meiosis occurs and  haploid meiospores  are formed. They come out after rupture of the germ sporangium wall and develop into new mycelia.

18. Economic Importance- They are commercially used to produce various chemicals and alcoholic products. R. oryzae   is used in the production of cortisone and lactic acid. R. oryzae   is also used for biosorption of heavy metals in wastewater. R. stolonifer  is used to produce lactic acid, fumaric acid and cortisone. R. delemar  is used to produce biotin and fumaric acid. Tempeh , a traditional soybean fermented product of Asia, is prepared using  Rhizopus   species. Many traditional alcoholic beverages, e.g. Parakari (cassava product), is prepared using  Rhizopus .