Let’s know about Zygomycota. Zygomycota , or zygote fungi , are a former division or phylum of the fungal kingdom . The members are now part of two phyla Mucoromycota and Zoopagomycota. [1] About 1060 species are known. [2] They are mostly terrestrial in habitat, living in soil or on decaying plant or animal material. Some are parasites of plants, insects and small animals, while others form symbiotic relationships with plants. [3] Zygomycete hyphae can be coenocytic , forming septa only where gametesare formed or give off dead hyphae. The Zygomycota is no longer recognized because it was not thought to be truly monophyletic .
Word – medium
The name Zygomycota refers to the specially formed zygosporangia by members of this clade, in which resistant spherical spores are formed during sexual reproduction . Zygos is Greek for “joining” or ” yoke for one “, referring to the fusion of two hyphal strands which produces these spores, and -mycota is a suffix referring to a division of the fungus.
spores
The term “spore” is used to describe the structure related to diffusion and dispersal. Zygomycete spores can be formed both sexually and asexually. The spore is in a dormant state before germination. During this period, the metabolic rate is very low and can last from a few hours to several years. There are two types of sleep. Exogenous latencies are controlled by environmental factors such as temperature or nutrient availability. Endogenous or constitutional dormancy depends on the characteristics of the spore itself; For example, metabolic features. In this type of dormancy, germination can be stopped even when environmental conditions are favorable for growth.
mitospores
In zygomycetes, mitospores (sporangiospores) are formed asexually. They form into specialized structures, the mitosporangia (sporangia) that contain from a few to several thousand spores, depending on the species. Mitosporangia are carried by special hyphae, mitosporangiophores (sporangiophores). These specialized hyphae usually show negative gravity and positive phototropism allowing good spore dispersal. The wall of the sporangia is thin and easily destroyed by mechanical stimuli (eg raindrops, passing animals), leading to the spread of ripe mitospores. The walls of these spores contain sporopollenin in some species. Sporopollenin is formed from β-carotene and is very resistant to biological and chemical degradation. Zygomycete spores can also be classified with respect to their persistence:
chlamydospores
Know about Zygomycota, now know chlamydospores. Chlamydospores are asexual spores that are different from sporangiospores. The primary function of chlamydospores is the persistence of the mycelium and they are released when the mycelium is degraded. There is no mechanism for dispersal in chlamydospores. The formation of chlamydospores in zygomycetes is usually intercellular. However, it can also be terminal. According to their function, chlamydospores have a thick cell wall and are pigmented.
zygophorus
To know about Zygomycota now know zygophorus. Zygophores are chemotropic aerial hyphae that are the sex organs of Zygomycota, except for Phycomycetes in which they are not aerial but are found in the substrate. They have two different mating types (+) and (-). The opposite mating types move towards each other due to the volatile pheromones released by the opposite filaments, mainly trisporic acid and its precursors. Once two opposite mating types have made initial contact, they go through several stages to give rise to a zygospore.
The formation of zygospores is the result of a multi-step process that begins with the movement of zygophores of the corresponding mating type towards each other. Once contact is made between the zygophores, their walls stick to each other, flatten, and then the contact site is called the fusion septum. The tips of the zygophore become deformed and are called progametangia. A septum develops by gradual inward expansion until it separates the terminal gametangia from the progametangial base. At this point the zygophore is said to be in suspension. Vesicles accumulate in the fusion septum at which point it begins to dissolve. A little before the fusion septum completely dissolves, The primary outer wall begins to thicken. This can be seen as a dark spot on the primary wall as the fusion septum dissolves. These dark spots on the wall will eventually develop into warty formations that make up the wall thickness of the zygospore. As the zygospore grows, so do the wart structures until the entire cell is embedded around it. At this point, electron microscopy can no longer penetrate the wall. Eventually the warts push through the primary wall and darken which is likely due to melanin. Electron microscopy can no longer penetrate the wall. Eventually the warts push through the primary wall and darken which is likely due to melanin. Electron microscopy can no longer penetrate the wall. Eventually the warts push through the primary wall and darken which is likely due to melanin.
Meiosis usually precedes zygospore germination and there are a few main types of distinct nuclear behavior. Type 1 occurs when nuclei fuse quickly within a few days, resulting in haploid nuclei in the mature zygote. Type 2 occurs when some nuclei are not paired and instead degenerate, delaying meiosis until germination. Type 3 occurs when haploid nuclei continue to divide mitotically and then some join in clusters and some not. As a result, diploid and haploid nuclei are found in the germ sporangium.
Cell wall
To know about Zygomycota, now know about cell wall. Zygomycetes exhibit a special structure of the cell wall. Most fungi have chitin structurally as the polysaccharide whereas zygomycetes synthesise, chitosan, the deacetylated homopolymer of chitin. Chitin is composed of β-1,4 bonded N – acetyl glucosamine. Fungal hyphae grow at the ends. Therefore, specialized vesicles, the chitosome, bring chitin and its synthesis enzyme, the precursor of chitin synthetase, outside the membrane by exocytosis. The enzyme on the membrane catalyzes glycosidic binding structures from the nucleotide sugar substrate, uridine diphosph – N -acetyl-D-glucosamine. The nascent polysaccharide chain is then cleaved by the enzyme chitin deacetylase. The enzyme chitin contains N-Catalyzes the hydrolytic cleavage of the acetamido group. The chitosan polymer chain then forms microfibers. These filaments are embedded in an amorphous matrix containing proteins, glucans (which basically cross-link chitosan fibers), mannoproteins, lipids and other compounds. [5] [6]
trisporic acid
Trisporic acid is a C-18 terpenoid compound synthesized through the beta-carotene and retinol pathways in zygomycetes. It is a pheromone compound that is responsible for sexual differentiation in those fungal species. [7]
history
Trisporic acid was discovered in 1964 as a metabolite that increased carotene production in Blacksley Trispora . Later it was shown that it is the hormone that produces the zygophore in the mucor mucosa . [8]American mycologist and geneticist Albert Francis Blaxley found that some species of Mucorales were self-sterile (heterothallic), requiring the interaction of two strains, designated (+) and (-), for initiation of sexual activity. This interaction, Hans Bergaff of the University of Goettingen, found that it is caused by the exchange of low-molecular-weight substances that diffuse through the substrate and the atmosphere. This work was the first demonstration of sex hormone activity in any fungus. The elucidation of the hormonal control of sexual contact in Mucorales spans over 60 years and includes mycologists and biochemists from Germany, Italy, the Netherlands, the UK and the USA. [8]
Functions of Trisporic Acid in Mucorales
The identification of compatible sex partners in Zygomycota is based on the cooperative biosynthesis pathway of trisporic acid. Early trisporoid derivatives and trisporic acid induce the swelling of two potential hyphae, hence called zygophores, and a chemical gradient of these effector molecules results in growth towards each other. These progametangia come into contact with each other and form a strong connection. In the next stage, septa are established to delimit the developing zygospore from the vegetative mycelium and thus the zygophores become suspensor hyphae and gametangia are formed. After the fusion wall dissolves, cytoplasm and a high number of nuclei from both gametangia are mixed. A selection process (unstudied) results in the reduction of nuclei and leads to meiosis (not studied to date). multiple cell wall modifications,
Trisporic acid, as the endpoint of this recognition pathway, can be produced solely in the presence of both compatible partners, which enzymatically generate trisporoid precursors for further use by the potential sexual partner. The species specificity of these reactions is achieved by spatial isolation, physicochemical characteristics (volatility and photosensitivity) of derivatives, chemical modifications of trisporoids, and transcriptional/posttranscriptional regulation, among others.
parasexualism
Trisporoids are also used in mediating recognition between parasite and host. An example is host–parasite interactions of parasexual nature, observed between Parasitella parasitica , an alternative mycoparasite of zygomycetes, and Absidia glauca . This interaction is an example for biotrophic fusion parasitism, as genetic information is transferred to the host. Many morphological similarities are observed in comparison to zygospore formation, but the mature spore is called cyclospore and is parasitic. During this process, the host Absidia glaucaBile-like structures are produced by This, together with further evidence, has led to the notion that trisporoids are not strictly species-specific, but they may represent a general principle of mating recognition in Mucorales. [9]
phototropism
Light regulation has been investigated in the zygomycetes Phycomyces blaxlinus , Mucor circineloides and Pilobolus crystallius . For example, in Pilobolus crystallinus the light is responsible for the dispersion mechanism and the sporangiophores of Phycomyces blakeslinus move towards the light. When light, particularly blue light, is involved in the regulation of fungal growth, it directs the development of fungal structures and activates metabolic pathways. For example, Zygomycota use light as a signal to promote vegetative reproduction and the growth of aerial hyphae to facilitate spore dispersal.
Fungal phototropism has been investigated in detail using the sporangiophore , the fruiting body of Phycomyces , as a model . Phycomyces have a complex photoreceptor system. It is able to respond to different light intensities and different wavelengths. Unlike the positive response to blue light, UV light also has a negative reaction. Reactions also seen on red light
Activation of beta-carotene biosynthesis by light
Two genes for the enzymes phytoene desaturase (carB) and the bi-functional phytoin synthase/carotene cyclase (carRA in Phycomyces , carRP in Mucor ) are responsible for the synthesis of beta-carotene. The product of the gene crgA, which was found in Mucor, suppresses the formation of carotenes by inhibiting the accumulation of carB and carRP mRNAs.
Effect of light on sporulation and sexual development
The zygomycete P. bleckslinus produces two types of spongiophores , macrophores and microphores which differ in size. The formation of these sporangiophores act on different light fluxes and hence with specific photoreceptors. Light also controls asexual sporulation. In mucor , the product of the crgA gene acts as an activator. In contrast, sexual development of Phycomyces is inhibited by light due to a specialized photoreceptor system.
gravity
Gravitropism is a turning or growth movement by a plant or fungus in response to gravity. It is equally widespread in both the states. Statolytes are required in both fungi and plants for the mechanism of gravity-sensing. Zygomycota sporangiophores arise from specialized “basal hyphae” and undergo several distinct developmental stages until the release of mature asexual spores. In addition to positive phototropism, sporangiophores are directed to a position suitable for spore dispersal and distribution by a negative gravitational response. Both reactions are growth reactions i.e. the orientations are caused by differential growth on the respective opposite sides of the sporangiophore, and affect each other. PhycomycesThe only model for the mechanism of the gravitational response of the vacuole is based on the ability of the vacuole to float within the surrounding cytoplasm . [10]The resulting asymmetric distribution of cytoplasm is proposed to generate increased wall growth on the lower side of horizontally placed sporangiophores because the number of vesicles secreting cell-wall material formed in the thick cytoplasmic layer will be greater than on the upper side . , Gravitropic bending begins after approximately 15–30 min in horizontally placed sporangiophores and continues until approximately 12–14 hours after the sporangiophore tip has regained its original vertical position. Generally, the gravitational response is weaker than that of the phototrophic. However, in some situations, equilibrium can be established and the reactions are comparable. In plants and fungi, phototropism and gravitropism interact in complex ways. The sporangiophore (fruiting body) of the zygomycete fungus, during continuous irradiation with unilateral light,[11] )।
Protein crystals involved in graviperception
Phycomyces blakesleeanus The wild-type sporangiophores contain large, easily seen octahedral paracrystalline crystals with sizes up to 5 × 5 × 5 µm. Generally, they are found near the main vacuole in clusters containing more than ten crystals. They are often attached to the vacuole transept. Sedimentation with a speed of about 100 µm/s can be observed when the sporangiophores are tilted. Glide or pull on vacuolar membranes and transepts during sedimentation serves as an inter-cellular signal for a potential cytoskeleton response, And it activates receptors located in the cell membrane. These receptors in turn trigger a chain of events that eventually leads to anomalous growth of the cell wall. Studies of the inclination angle of the wild-type and mutant strain sporangiophore development have shown that the mutant strains do not have crystals that reduce the gravitational response
Lipid droplets are involved in graviperception
The complex of apical lipid globules is also involved in graviperception. These lipids are clustered into cellular structures, complexes of lipid globules, approximately 0.1 mm below the very tip of the apex. (Fig. 2) Upon formation of the sporangium, the globules move to the columella. In the mature state, this complex is believed to act as a gravity receptor due to its ability to float. Mutants that lack this lipid complex have a much lower gravitational response [10]
phylogeny
Historically, all fungi producing a zygospore were considered related and placed in the Zygomycota. The use of molecular phylogenetics has increasingly revealed this group to be paraphyletic. [1] However, the rank (i.e., phylum or subphylum) of these clades is in dispute. A phylogeny of fungi with zygomycetes subphyla obtained from Spataphora et al. is as follows. (2016) [1] with both possible phylum names.
industrial application
Many species of zygomycetes can be used in important industrial processes. One of them is presented in the resume table.
| Caste | the product | Use |
|---|---|---|
| Many Mucor and Rhizopus spp. | lipase and protease | Leather, detergent and medical industry (steroid transformation) |
| rhizopus | cellulase | Food production (ie, tempeh) |
| R. oryzae , other Rhizopus spp. | fumaric acid | Miscellaneous |
| Rhizopus spp. | Lactic acid | Miscellaneous |
| R. delamaro | biotin | Miscellaneous |
| Mortarella romaniana , Mortarella vinacea and Mucor indications | linolenic acid | Miscellaneous |
| mortirella alpina | arachidonic acid | Miscellaneous |
| Blacksley Trespora | β carotene | Miscellaneous |
state of culture
Zygomycetes are able to develop in a wide range of environments. Most of them are mesophilic (growing at 10–40 °C with an optimum 20–35 °C), but some, such as Mucor mihei or Mucor pusillus , are thermophilic, with a minimum growth temperature of around 20 °C and a maximum The temperature is rising. 60 °C. Others such as Mucor Himalis can grow at temperatures below 0 °C.
Some species of the order Mucorales are capable of growing in anaerobic conditions, while most of them require aerobic conditions. Furthermore, while most zygomycetes only develop in high water activities, some of them are capable of growing at salt concentrations of as low as 15%. Most species of Mucor grow rapidly on agar at room temperature, with Petri dishes filling with their thick aerial mycelium in 2–3 days. When incubated in liquid culture under semi-anaerobic conditions, many species develop to a yeast-like state. Zygospore formation can be stimulated at high temperatures of incubation (30–40 °C).
Zygomycota growth in solid agar can produce a low or very high fibrous colony that rapidly fills an entire Petri dish. Its color can range from pure white to gray or brown. In older cultures, deeply pigmented sporangia are seen. Everything depends on the species and the media used. In liquid culture, the zygomycota usually form a soft mass and do not produce spores. This is because they cannot develop aerial hyphae.
culture media
Zygomycetes grow well on most standard fungal culture medium such as Sabourad Dextrose Agar. They can also grow on both selective and non-selective mediums. Minimal media, supplementary media and induction media can also be used. Most zygomycetes are sensitive to cycloheximide (Actidione) and this agent should not be used in culture media.
Reproduction
A common example of a zygomycete is the black bread mold ( Rhizopus stolonifer), a member of the Mucorales. It spreads over the surface of bread and other food sources, sending the hyphae inward to absorb nutrients. In its asexual stage it develops bulbous black sporangia directly on the tips of the hyphae, each containing hundreds of haploid spores.
Like most zygomycetes, asexual reproduction is the most common form of reproduction. rhizopusSexual reproduction in stolonifers, as in other zygomycetes, occurs when haploid hyphae of different mating types are in close proximity to each other. Gametangia begin to develop after exposure to gametangia, and plasmogamy, or fusion of the cytoplasm, occurs. Karyogamy, which is the fusion of nuclei, follows closely after this. The zygosporangia are then diploid. Zygosporangia are typically thick-walled, highly resilient to environmental difficulties, and metabolically inactive. However, when conditions improve, they germinate to produce a spore or vegetative hyphae. Meiosis occurs during the germination of the zygosporangium, so the resulting spores or hyphae are haploid. Grows in warm and moist conditions.
Some zygomycetes disseminate their spores in a more precise manner than by allowing air currents to flow aimlessly. Pilobolus , a fungus that grows on animal dung, bends its sporangiophores to light with the help of a photosensitive pigment (beta-carotene) and then “fires” them with an explosive torrent of high-pressure cytoplasm . The sporangia can be launched up to 2 m, placing them far away from the dung and hopefully on vegetation that would be eaten by a herbivorous, eventually deposited with the dung elsewhere. Different mechanisms for forced spore discharge have evolved among members of the zygomycete order Entomophthorales.
development of conidia
The evolution of conidium from sporangiospore is defining the main difference between zygomycetes and Ascomycetes. [12] The development of conidia of sporangiospores typical of zygomycetes, similar to those found in ascomycetes, can be produced by a range of forms seen in zygomycetes. Many zygomycetes produce multiple sporogenic spores inside a single spore. Some have developed numerous small sporangiola containing few sporangiospores. In some cases, each sporangiolum may contain up to three spores, and some species have sporangiola that contain only one spore. choenephora, a zygomycete, has a sporangiolum containing a spore with a sporangium wall visible at the base of the sporangium. This structure is similar to that of a conidium, consisting of two, fused cell walls, an inner spore wall, and an outer spore wall.
