Spirogyra Definition, Classification, and Morphology of Spirogyra

Spirogyra Definition

Spirogyra DefinitionSpirogyra is a green alga that occurs mainly in fresh water in the form of lumps. These are also known as water silk or mermaid braids.

  • It is a unicellular organism, but it can be seen in freshwater bodies when it agglomerates into a multicellular structure.
  • Spirogyra is composed of chlorophyll, which gives it a green appearance. It also allows you to prepare your food.
  • Spirogyra is a thread-like green freshwater alga that is easier to recognize by its spiraling chloroplasts.
  • Spirogyra spp. They are unbranched filamentous algae that have a unique model of sexual reproduction.

Classification of Spirogyra

About 400 species of Spirogyra are found in various freshwater bodies around the world.

The following is the taxonomic classification of Spirogyra described or suggested by E. Fritsch (1935) in his book “The Structure and Reproduction of Algae”:

Domain: Eukarya

Kingdom: Protista or Protoctista

Phylum: Chlorophyta

Class: Chlorophyceae

Order: Zygnematales

Family: Zygnemataceae

Genus: Spirogyra

Habitat of Spirogyra

  • Green algae, spirogyra (Chlorophyta), are found in a wide variety of habitats, including small standing bodies of water, rivers, and streams.
  • It is also part of the vegetation on the edges of large lakes and rivers.
  • Spirogyra exists in a filamentous form which often forms floating masses near streams and ponds, fed by oxygen bubbles released during photosynthesis.
  • Some species of Spirogyra are found in streams and rivers with low flow, where they appear as green tufts.
  • They are also found in temporary ponds, which have a short lifespan, where they bloom in wet weather and dry out later.
  • These are photosynthetic with chlorophyll as the photosynthetic pigment, making them an essential part of the aquatic ecosystem.

Morphology of Spirogyra

  • Spirogyra is a long, multicellular, filamentous green algae made up of cells linked end to end to form long chains. These strands or chains can be several inches long.
  • The vegetative structure of Spirogyra is called the thallus, which is the unbranched, filamentous strand made up of several cells.
  • The cells of the filament are 10 to 100 µm long and have a cylindrical structure. Each cell of the filament is connected to two cells across its width, except for the cells at each end, which are only connected to one cell at a time.
  • The terminal cell of the filament may not be green in some species and is known as retention. Some species, such as Spirogyra longata, also have root-shaped rhizoids that arise from the handle that supports the substrate filaments.
  • Cells with a filamentous structure are characterized by one or more spiral chloroplasts, which give the organism its characteristic green color.
  • The cell wall of each cell consists of two layers; the inner layer of cellulose and the outer layer of pectin. These layers are responsible for the slippery texture of the body.
  • Under the microscope, Spirogyra appears surrounded by a viscous, gelatinous substance that represents the outer wall of the body dissolved in water. In addition, the filaments are also surrounded by mud, which holds the filaments together to form clumps in the water.
  • The wall between two cells consists of the middle lamella, which can be flat, replicated or connected.
  • Most of the interior of the cell is occupied by the large central vacuole that surrounds the nucleus, which is suspended by delicate strands of cytoplasm.
  • In addition to the large vacuole, the cytoplasm also consists of the chloroplast, which wraps around the vacuole and is made up of specialized bodies, the pyrenoids. Pyrenoids are unique structures with a central protein nucleus that stores starch.
  • With the exception of the clamp, all other cells in the filament can divide and increase the length of the filament.

Cultural characteristics of Spirogyra

  • The morphological characteristics of algae are the essential characteristics to identify most algae. However, some cultural characteristics of algae may also be necessary for identification.
  • Spirogyra can be grown on BG-11 medium with other green algae. But also Bold’s base medium with triple nitrate and vitamins is considered a suitable medium for the growth of Spirogyra species.
  • Algae grow slower than bacteria, and with Spirogyra it takes several weeks to get a dense culture of algae from a single cell.
  • During cultivation, concentrations of phosphate and nitrate are added to the algae suspension twice a week as needed.
  • Typical signs of sigma growth in Spirogyra are a brief lag phase followed by exponential growth.
  • As the culture density increases, the medium may turn dark green and the supernatant from the centrifuged samples becomes more and more red and viscous, which is probably due to the production of mucus from Spirogyra, which is a defense strategy against epiphytes.
  • Spirogyra grows in the form of green filaments which together form green tufts along the plates or bioreactors.
  • The length of the filaments can vary from 100 to 600 µm with a width of 10 to 100 µm depending on the species.
  • In addition, the shape of gametangia and zygospores can also vary from species to species, which helps identify the organism.

Life Cycle of Spirogyra

Spirogyra’s life cycle unfolds in three ways; vegetative, asexual and sexual. Vegetative and sexual cycles are more frequent than asexual cycles.

A generational shift is shaping the life cycle of Spirogyra. This is the haploid sense, the organism’s haploid gametophytic structure is the elongated structure, followed by a short diploid zygospore as a sporophytic structure.

This is observed during sexual reproduction, where the life cycle of the organism alternates between the haploid filament and the diploid zygospore.

The zygospore is the only diploid phase of the sexual life cycle. After fusion, the female gametange breaks down to release the zygospore.

The zygospore remains at the bottom of the pond until a favorable condition is established.

The zygospore then divides meiotically and forms four haploid nuclei, only one of which survives.

The zygospore then slowly grows and bursts to release the germ tube. The germ tube is then divided several times crosswise to form a haploid filament.

Reproduction in Spirogyra

Vegetative and sexual reproduction in Spirogyra is common, while asexual reproduction occurs occasionally.

Vegetative reproduction

  • Vegetative reproduction in Spirogyra is the shortest method of reproduction which occurs by fragmentation.
  • Spirogyra can reproduce by fragmentation, whereby the body’s vegetative filament breaks down into fragments, each of which independently develops into a new filament.
  • The fragment passes through several divisions to form an elongated vegetative filament.
  • Under favorable conditions, fragmentation is the most common method of reproduction in Spirogyra.
  • Mechanical damage, dissolution of the central lamella, or formation of H-shaped fragments can lead to filament breaks in individual fragments.

Asexual reproduction

Asexual reproduction is less common in Spirogyra but occurs in some species under unfavorable conditions through the formation of asexual spores such as aplanospores, acynets and zygospores.

 Aplanospores

  • Aplanospores are formed under unfavorable conditions when the cytoplasm of the cell contracts and a wall forms around it.
  • Aplanospores are not motile and, under favorable conditions, ultimately lead to the formation of a filament.
  • Aplanospora is the only method of reproduction in S. aplanospora.

Akinetes

  • In some species of Spirogyra, the cell develops a thick wall around it to protect itself from adverse conditions.
  • As soon as the conditions are favorable, the Akinet develops into a filament. It is common in S. farlowii.

Azygospores

  • In S. varians, the gametes sometimes fail to fuse during sexual reproduction and are surrounded by a thick cell wall that forms an azygospore.
  • Like other asexual spores, azygospores develop into a new filament.

 Sexual reproduction

  • Sexual reproduction in Spirogyra occurs by changing from a haploid filament to a diploid zygospore.
  • Conjugation is the method of sexual reproduction in Spirogyra, which involves the fusion of two gametes of opposite strains. The entire protoplasmic content of the cell acts like a gamete.
  • Gametes are morphologically identical, but upon conjugation one of the gametes becomes active (male gametes) while the other becomes passive or immobile.
  • The conjugation in Spirogyra is of two types; Scalar form and lateral conjugation

Scalariform Conjugation

  • This is the most common type of conjugation that occurs between two different filaments when the two filaments come together and are parallel to each other.
  • Then the opposing cells develop bumps or growths that spread and come into contact with each other.
  • The top of these growths dissolves to form a mating tube between the two cells.
  • This leads to the formation of a ladder-like (scalar-shaped) structure along the filament.
  • During this time, the protoplasm of the cells is rounded to form gametes, and the motile male gametes move through the conjugation tube to reach the female gametes.
  • The fusion of these gametes results in the formation of a zygote, which is diploid. The zygote develops a thick wall to form a zygospore.

Lateral Conjugation

Lateral conjugation is less frequent and occurs between two neighboring cells of the same filament. This can be done in two other ways; Indirect and direct lateral conjugation

Indirect lateral conjugation

  • Indirect lateral conjugation creates growths on the sides of the septum which ultimately leads to the formation of an opening on the lateral side of the cells.
  • One of the two neighboring cells acts as male gametangia while the other acts as female gametangia.
  • The male gamete then moves through the tube and merges with the female gamete to form a zygote.
  • In species that reproduce by indirect lateral conjugation, a zygospore forms in all other cells of the filament.
  • It occurs in Tenuissima, S. affinis, etc.

Direct lateral conjugation

With direct lateral conjugation, a pore is formed in the septum which is large enough for the passage of male gametangia.

The male gametes are then transferred through the pores into the female gametes, where they fuse into a diploid zygote.

It occurs in S. jogensis.

Identification of Spirogyra

The main method of identification of Spirogyra is by observing the morphological structure of the organism, but other methods of identification are also available.

Cultural identification

  • Cultural identification of Spirogyra is possible by studying various morphological and physiological characteristics of the organism.
  • The length and width of the filament, the structure of the transverse wall (septum), the number of chloroplasts per cell and the number of turns of the chloroplasts, and the type of vegetative cells are some of the characteristics.
  • In addition, the species can also be identified by the structure of the reproductive spores and the type of mating.
  • The size of the zygospore and the nature of the spore membrane are also examined for correct identification.

Molecular identification

  • Molecular identification methods can also be used for better and more detailed identification of the species.
  • The most common method of identifying the organism using a molecular technique is DNA sequencing.
  • In DNA sequencing, DNA is first extracted and purified, followed by PCR amplification.
  • Purified PCR products can be sequenced directly using a variety of sequencing tools.
  • Based on the results of molecular and molecular identification methods, a molecular phylogeny of the species Spirogyra can be established.

The following table provides some characteristics of some Spirogyra species that can be used for identification:

Economic Importance / Applications / Uses of Spirogyra

  • Some species of Spirogyra are used as a food source in different parts of the world because they are rich in vitamins and minerals.
  • Green algae like Spirogyra are also an important part of aquatic ecosystems as they perform photosynthesis and therefore provide oxygen to other organisms in the water. They are also the producers of the ecosystem.
  • Spirogyra is also considered to be an essential source of several natural bioactive compounds which can be used for antibiotic, antioxidant and anti-inflammatory purposes.
  • Some species of Spirogyra have potential for municipal wastewater treatment and biomass production for biofuel applications.
  • A particular Himalayan species of Spirogyra, S. porticalis, has been shown to produce thirteen known bioactive chemotypes of plant protection importance, including fatty acid esters, sterols, unsaturated alcohols, and alkynes.
  • Spirogyra neglencea was found to have cancer chemopreventive compounds and activity against lesions (which are at high risk of becoming cancerous) in rat liver. This could have a significant impact on cancer research and the treatment of similar liver cancers in humans.

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Spirogyra Definition, Classification, and Morphology of Spirogyra

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