Genus Spirogyra – An Overview

Spirogyra is a genus of filamentous green algae that belongs to the phylum Chlorophyta and the class Zygnematophyceae. The name Spirogyra comes from the Greek words "spira" meaning coil and "gyros" meaning ring, referring to the spiral arrangement of the chloroplasts inside the cells. Spirogyra is also known by various common names, such as water silk, mermaid`s tresses, and blanket weed .

Spirogyra is a unicellular organism, but it forms long chains of cells that are attached end-to-end, creating multicellular filaments. These filaments can grow up to several centimeters in length and can form dense mats or clumps on the surface of freshwater habitats. Spirogyra is widely distributed around the world and can be found in ponds, lakes, streams, rivers, and ditches.

Spirogyra is a photosynthetic organism that uses chlorophyll as the main pigment to capture light energy and convert it into chemical energy. The chloroplasts in Spirogyra are ribbon-like structures that coil around the central vacuole of each cell, giving the algae a characteristic green color. The chloroplasts also contain specialized structures called pyrenoids, which are involved in starch synthesis and storage.

Spirogyra is an important part of the aquatic ecosystem, as it produces oxygen and organic matter that support other organisms. However, Spirogyra can also cause problems when it grows excessively and forms thick mats that block sunlight and reduce oxygen levels in the water. This can affect the biodiversity and water quality of the habitat. Spirogyra can also be used as a source of food, bioactive compounds, and biofuel.

Spirogyra is a fascinating organism that has a unique morphology and reproduction. In this article, we will explore the classification, habitat, morphology, cultural characteristics, life cycle, reproduction, identification, and economic importance of Spirogyra.

Spirogyra belongs to the domain Eukarya, which includes all organisms with a nucleus and other membrane-bound organelles. Within this domain, Spirogyra is classified under the kingdom Plantae, which comprises mainly multicellular photosynthetic organisms that can produce their own food using chlorophyll. Spirogyra is a member of the phylum Chlorophyta, also known as green algae, which contains about 4,300 species of mostly freshwater organisms that have chloroplasts with a characteristic green color. Spirogyra is further classified under the class Zygnematophyceae, which consists of about 4,000 species of filamentous or colonial green algae that have a unique mode of sexual reproduction involving conjugation. Spirogyra is placed in the order Zygnematales, which includes green algae with unbranched filaments that can form masses or mats on the surface of water bodies. Spirogyra belongs to the family Zygnemataceae, which is characterized by having one or more spiral chloroplasts per cell and producing zygospores as a result of conjugation. Finally, Spirogyra is the genus name for over 400 species of green algae that have a helical or spiral arrangement of the chloroplasts that gives them their common name of water silk or mermaid`s tresses.

The following table summarizes the taxonomic classification of Spirogyra according to E. Fritsch (1935) in his book "The Structure and Reproduction of the Algae":

The classification of Spirogyra can also be based on molecular methods such as DNA sequencing, which can reveal the phylogenetic relationships among different species and genera of green algae. Based on molecular data, some researchers have proposed to divide Spirogyra into several subgenera or sections based on the number and shape of the chloroplasts, the structure of the zygospores, and the type of conjugation. However, these classifications are not widely accepted and need further confirmation.

• Spirogyra is a green algae that is mostly found in freshwater habitats, such as ponds, lakes, streams, rivers and ditches.
• It can grow in a wide range of environmental conditions, such as temperature, pH, light intensity and nutrient availability.
• It is often observed as green slimy patches on the ground near water bodies, due to the mucilage that surrounds the filaments and holds them together.
• It can also form floating masses on the surface of water, buoyed by oxygen bubbles released during photosynthesis.
• It is sometimes found attached to the substratum by root-like structures called rhizoids or holdfasts.
• It is a photosynthetic organism that contains chlorophyll and can prepare its own food.

• It is an important part of the aquatic ecosystem, as it provides oxygen and organic matter to other organisms.

  Morphology of Spirogyra

Spirogyra is a filamentous green alga that has a simple vegetative structure called thallus. The thallus consists of cylindrical cells that are joined end to end to form long, unbranched filaments . The filaments can be several centimeters long and 10-100 µm wide . The filaments are surrounded by a slimy mucilage sheath that gives them a slippery texture and helps them to form clumps or mats in water .

Each cell in the filament has a cell wall, a cell membrane, a cytoplasm, a nucleus, a vacuole, and one or more chloroplasts . The cell wall is composed of two layers: an inner layer of cellulose and an outer layer of pectin . The cell membrane is located beneath the cell wall and regulates the movement of substances in and out of the cell. The cytoplasm is the fluid that fills the cell and contains various organelles and inclusions. The nucleus is the control center of the cell that contains the genetic material (DNA) and a nucleolus . The vacuole is a large, central organelle that occupies most of the cell volume and stores water, salts, and other substances . The vacuole is separated from the cytoplasm by a membrane called tonoplast.

The most distinctive feature of Spirogyra is its chloroplasts, which are ribbon-shaped organelles that contain the green pigment chlorophyll . Chlorophyll enables Spirogyra to perform photosynthesis, which is the process of converting light energy into chemical energy (sugars). The chloroplasts are arranged spirally around the vacuole, giving Spirogyra its name and appearance . The number and shape of chloroplasts vary among different species of Spirogyra. Some species have one chloroplast per cell, while others have two or more . Some species have smooth-edged chloroplasts, while others have serrated or lobed edges . Within each chloroplast, there are specialized structures called pyrenoids, which are protein-rich bodies that store starch . Pyrenoids are also involved in carbon fixation, which is the incorporation of carbon dioxide into organic molecules.

The cells in the filament are connected by transverse walls called septa . The septa have pores that allow the passage of cytoplasmic strands between adjacent cells . These strands help to maintain the continuity and coordination of the filament. The septa can also have different shapes depending on the species. Some species have plane septa, while others have replicate or colligate septa . The terminal cell of the filament may have a non-green holdfast, which is a specialized structure that anchors the filament to the substratum . Some species also have root-like rhizoids that extend from the holdfast and help to attach the filament to the surface.

The morphology of Spirogyra is important for its identification, as different species have different characteristics such as length and width of filaments, number and shape of chloroplasts, type of septa, presence or absence of holdfast and rhizoids, etc.

The following table summarizes some morphological features of some common species of Spirogyra:

Cultural characteristics of Spirogyra

Cultural characteristics of Spirogyra are the features that can be observed or measured when the organism is grown in a suitable medium under controlled conditions. These characteristics can help in the identification and classification of different species of Spirogyra.

Some of the cultural characteristics of Spirogyra are:

• Green algae, including Spirogyra, can be grown in BG-11 medium. However, Bold’s Basal Medium with triple nitrate and vitamins is also considered a suitable medium for the growth of Spirogyra species.
• It takes several weeks to get a dense Spirogyra culture from a single cell, and even longer when compared to the growth rate of bacteria.
• The algal suspension may have phosphate and nitrate added to it at varying amounts twice weekly during cultivation.
• The typical sigmoidal growth characteristics in Spirogyra consist of a short lag phase followed by exponential growth.
• As the density of the culture increases, the medium might turn dark green, and the supernatant of the centrifuged samples is found to become increasingly red and viscous, which most likely be caused by mucilage production of Spirogyra, which is a strategy of defending itself against epiphytes.
• Spirogyra grows in the form of green filaments that together form green clumps throughout the plates or bioreactors.
• Depending on the species, the length of the filaments can range from 100-600 µm with the width ranging from 10-100 µm.
• Besides, the shape of the gametangia and zygospores might also range between different species which helps in the identification of the organism.
• The size of the zygospore and the nature of the spore membrane are also studied to obtain proper identification.

Life Cycle of Spirogyra

The life cycle of Spirogyra occurs via one of the three ways; vegetative, asexual, and sexual. The vegetative and sexual cycles are more common than asexual cycles . A form of alternation of generation characterizes the life cycle of Spirogyra. It is haploidic meaning, the haploid gametophytic structure of the organism is the prolonged structure followed by a brief diploid zygospore as the sporophytic structure . This is observed during sexual reproduction where the life cycle of the organism alternated between the haploid filament and the diploid zygospore .

The zygospore is the only diploid phase in the sexual life cycle. After fusion, the female gametangia undergo decay to release the zygospore . The zygospore remains at the bottom of the pond until a favorable condition is present . The zygospore then divides meiotically to form four haploid nuclei, out of which only one survives . The zygospore then slowly grows in size and bursts to release the germ tube. It is followed by repeated transverse divisions of the germ tube to form a haploid filament .

Vegetative reproduction

Vegetative reproduction in Spirogyra is the shortest method of reproduction that occurs via fragmentation . Spirogyra can multiply by fragmentation where the vegetative filament of the organism breaks into fragments, each of which independently develops into a new filament . The fragment undergoes multiple divisions to form an elongated vegetative filament . Under favorable conditions, fragmentation is the most common method of reproduction in Spirogyra . The breakdown of the filament to form individual fragments might occur either due to mechanical injury, dissolution of the middle lamella, or the formation of H-shaped fragments .

Asexual reproduction

Asexual reproduction is less common among Spirogyra, but it occurs in some species under unfavorable conditions by means of the formation of asexual spores like aplanospores, akinetes, and zygospores .

• Aplanospores are formed under unfavorable conditions where the cytoplasm of the cell shrinks and a wall is formed around it . The aplanospore is non-motile and eventually leads to the formation of a filament once the condition is favorable . In S. aplanospora, the formation of aplanospores is the only method of reproduction.
• Akinetes are formed when some species of Spirogyra develop a thick wall around themselves to protect themselves from unfavorable conditions . Once the condition becomes favorable, the akinete develops to form a filament. It is common in S. farlowii.
• Azygospores are formed when in S. varians, sometimes the gametes fail to fuse during sexual reproduction and get enclosed by a thick cell wall forming an azygospore. Like other asexual spores, azygospores also develops to form a new filament.

Sexual reproduction

Sexual reproduction in Spirogyra occurs via alternation between a haploid filament and a diploid zygospore. Conjugation is the method of sexual reproduction in Spirogyra where the fusion of two gametes of opposite strains takes place. The entire protoplasmic content of the cell acts as the gamete. The gametes are morphologically identical, but during conjugation, one of the gametes becomes active (male gamete) while the other becomes passive or non-motile.

Conjugation in Spirogyra is of two types; Scalariform and Lateral Conjugation

• Scalariform Conjugation: It is the more common mode of conjugation that occurs between two different filaments when they come close and lie parallel to each other. Then opposite cells develop protuberances or outgrowths that extend and come in contact with one another. The top of these outgrowths then dissolves to form a conjugation tube between the two cells. This results in the formation of a ladder-like structure (scalariform) throughout the filament. Meanwhile, the protoplasm of the cells round up to form gametes, and the motile male gamete then moves through the conjugation tube to reach the female gamete. 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 often and occurs between two adjacent cells of the same filament. It might occur in two further ways; Indirect and Direct lateral conjugation.

  • Indirect lateral conjugation: During indirect lateral conjugation, outgrowths emerge on the sides of the septum, which eventually leads to the formation of an opening at the lateral side of the cells. One of the two adjacent cells acts as male gametangia, whereas the other acts as the female gametangia. The male gamete then moves through the tube and fuses with the female gamete to form a zygote. In species reproducing by indirect lateral conjugation, in every second cell of the filament, a zygospore is formed. It occurs in tenuissima, S. affinis, etc.
  • Direct lateral conjugation: During direct lateral conjugation, a pore is formed in the septum that becomes big enough for the male gametangia to pass trough. The male gamete is then transferred through the pore into the female gametangia where they fuse to form a diploid zygote. It occurs in S .jogensis.
    
    Reproduction in Spirogyra: Vegetative, Asexual and Sexual reproduction
    

Spirogyra can reproduce by three methods: vegetative, asexual and sexual reproduction. The most common mode of reproduction is vegetative reproduction by fragmentation, which occurs under favorable conditions. Asexual reproduction is rare and occurs by the formation of spores in some species. Sexual reproduction occurs by conjugation, which involves the fusion of gametes from different filaments.

Vegetative reproduction

• Vegetative reproduction in Spirogyra takes place by fragmentation under favorable conditions.
• In fragmentation, the filament breaks at cross walls into one or more segments or fragments.
• Each fragment may consist of a few living cells or even a single cell and each fragment grows into a new filament by repeated cell division and growth.
• Fragmentation can be due to mechanical injury, dissolution of the middle lamella, or the formation of H-shaped fragments.

Asexual reproduction

• Asexual reproduction is less common among Spirogyra and occurs in some species under unfavorable conditions by means of the formation of asexual spores like aplanospores, akinetes, and zygospores.
• Aplanospores are formed when the cytoplasm of the cell shrinks and a wall is formed around it. The aplanospore is non-motile and eventually leads to the formation of a filament once the condition is favorable. In S. aplanospora, the formation of aplanospores is the only method of reproduction.
• Akinetes are formed when the cell develops a thick wall around itself to protect itself from the unfavorable condition. Once the condition becomes favorable, the akinete develops to form a filament. It is common in S. farlowii.
• Zygospores are formed when the gametes fail to fuse during sexual reproduction and get enclosed by a thick cell wall forming an zygospore. Like other asexual spores, zygospores also develop to form a new filament. It occurs in S. varians.

Sexual reproduction

• Sexual reproduction in Spirogyra occurs via alternation between a haploid filament and a diploid zygospore.
• Conjugation is the method of sexual reproduction in Spirogyra where the fusion of two gametes of opposite strains takes place. The entire protoplasmic content of the cell acts as the gamete.
• The gametes are morphologically identical, but during conjugation, one of the gametes becomes active (male gamete) while the other becomes passive or non-motile (female gamete).
• Conjugation in Spirogyra is of two types; Scalariform and Lateral Conjugation.

Scalariform Conjugation

• It is the more common mode of conjugation that occurs between two different filaments when the two filaments come close and lie parallel to each other.
• Then the opposite cells develop protuberances or outgrowths that extend and come in contact with one another.
• The top of these outgrowths then dissolves to form a conjugation tube between the two cells.
• This results in the formation of a ladder-like structure (scalariform) throughout the filament.
• Meanwhile, the protoplasm of the cells round up to form gametes, and the motile male gamete then moves through the conjugation tube to reach the female gamete.
• 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 often and occurs between two adjacent cells of the same filament. It might occur in two further ways; Indirect and Direct lateral conjugation.

Indirect lateral conjugation

• During indirect lateral conjugation, outgrowths emerge on the sides of the septum, which eventually leads to the formation of an opening at the lateral side of the cells.
• One of the two adjacent cells acts as male gametangia, whereas the other acts as female gametangia.
• The male gamete then moves through the tube and fuses with female gamete to form a zygote.
• In species reproducing by indirect lateral conjugation, in every second cell of the filament, a zygospore is formed.
• It occurs in S. tenuissima, S. affinis, etc.

Direct lateral conjugation

• During direct lateral conjugation, a pore is formed in the septum that becomes big enough for the male gametangia to pass through.
• The male gamete is then transferred through the pore into the female gametangia where they fuse to form a diploid zygote.

• It occurs in S. jogensis.

  Identification of Spirogyra: Cultural and Molecular identification

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

Cultural identification

The 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), number of chloroplasts per cell, and number of turns of the chloroplast, and the type of the vegetative cells are some of the characteristics that can be used to distinguish different species.

Besides, species can also be identified based on the structure of the reproductive spores and the type of conjugation.

The size of the zygospore and the nature of the spore membrane are also studied to obtain proper identification.

Spirogyra can be cultured in different media such as BG-11 medium or Bold`s Basal Medium with triple nitrate and vitamins.

The growth characteristics, pigment composition, mucilage production, and biochemical properties of Spirogyra can also be used for cultural identification .

Molecular identification

For better and more detailed identification of the species, molecular identification methods can also be applied.

The most common method of identification of the organism using a molecular technique is DNA sequencing.

During DNA sequencing, the DNA is first extracted and purified, followed by amplification via PCR.

The purified PCR products can then be sequenced directly using various sequencing tools.

Based on the results from the molecular and molecular methods of identification, a molecular phylogeny of the species of Spirogyra can be prepared .

Molecular identification can also reveal the genetic diversity and evolutionary relationships among different species and genera of Spirogyra .

Molecular markers such as rbcL gene, ITS region, 18S rDNA gene, and trnL-F region can be used for molecular identification .

Molecular identification can also help to resolve some taxonomic uncertainties and controversies regarding some species and genera related to Spirogyra . For example, molecular analysis has shown that Sirogonium is part of a clade containing many species of Spirogyra, whereas Temnogyra might be a separate genus based on its unique morphology.

Some possible additional sentences to conclude are:

• Therefore, both cultural and molecular methods are useful for identifying Spirogyra species and understanding their diversity and evolution.

• In conclusion, Spirogyra is a diverse and complex genus that requires a combination of cultural and molecular methods for accurate identification and classification.

  Economic Importance / Applications / Uses of Spirogyra

Spirogyra is a green alga that has various economic importance, applications, and uses in different fields. Some of them are:

• Food source: Some species of Spirogyra are used as a source of food in different parts of the world as they are rich in vitamins and minerals . They are also eaten by fish and other aquatic animals.
• Aquatic ecosystem: Green algae like Spirogyra are also an important part of the aquatic ecosystems as they are photosynthetic and thus provide oxygen to other organisms in the water . They also help in maintaining the nutrient cycles and water quality in freshwater habitats.
• Bioactive compounds: Spirogyra is also considered as an essential source of various natural bioactive compounds that can be used for the antibiotic, antioxidant, and anti-inflammatory purposes. Some Spirogyra species have been found to have the potential for the treatment of cancer, liver lesions, and other diseases.
• Wastewater treatment and biofuel production: Some Spirogyra species have been found to have the potential for the treatment of municipal wastewater and biomass production for biofuel applications. They can remove pollutants like nitrogen, phosphorus, heavy metals, and organic matter from wastewater and produce biogas or biodiesel from their biomass.
• Fertilizer: Spirogyra can also be used as a fertilizer for crops as they contain nitrogen, phosphorus, potassium, and other minerals that can enhance soil fertility and crop yield. They can also improve soil structure and water retention capacity.

Cultural characteristics of Spirogyra are the features that can be observed or measured when the organism is grown in a suitable medium under controlled conditions. These characteristics can help in the identification and classification of different species of Spirogyra.

Some of the cultural characteristics of Spirogyra are:

• Green algae, including Spirogyra, can be grown in BG-11 medium. However, Bold’s Basal Medium with triple nitrate and vitamins is also considered a suitable medium for the growth of Spirogyra species.
• It takes several weeks to get a dense Spirogyra culture from a single cell, and even longer when compared to the growth rate of bacteria.
• The algal suspension may have phosphate and nitrate added to it at varying amounts twice weekly during cultivation.
• The typical sigmoidal growth characteristics in Spirogyra consist of a short lag phase followed by exponential growth.
• As the density of the culture increases, the medium might turn dark green, and the supernatant of the centrifuged samples is found to become increasingly red and viscous, which most likely be caused by mucilage production of Spirogyra, which is a strategy of defending itself against epiphytes.
• Spirogyra grows in the form of green filaments that together form green clumps throughout the plates or bioreactors.
• Depending on the species, the length of the filaments can range from 100-600 µm with the width ranging from 10-100 µm.
• Besides, the shape of the gametangia and zygospores might also range between different species which helps in the identification of the organism.
• The size of the zygospore and the nature of the spore membrane are also studied to obtain proper identification.

The life cycle of Spirogyra occurs via one of the three ways; vegetative, asexual, and sexual. The vegetative and sexual cycles are more common than asexual cycles . A form of alternation of generation characterizes the life cycle of Spirogyra. It is haploidic meaning, the haploid gametophytic structure of the organism is the prolonged structure followed by a brief diploid zygospore as the sporophytic structure . This is observed during sexual reproduction where the life cycle of the organism alternated between the haploid filament and the diploid zygospore .

The zygospore is the only diploid phase in the sexual life cycle. After fusion, the female gametangia undergo decay to release the zygospore . The zygospore remains at the bottom of the pond until a favorable condition is present . The zygospore then divides meiotically to form four haploid nuclei, out of which only one survives . The zygospore then slowly grows in size and bursts to release the germ tube. It is followed by repeated transverse divisions of the germ tube to form a haploid filament .

Vegetative reproduction

Vegetative reproduction in Spirogyra is the shortest method of reproduction that occurs via fragmentation . Spirogyra can multiply by fragmentation where the vegetative filament of the organism breaks into fragments, each of which independently develops into a new filament . The fragment undergoes multiple divisions to form an elongated vegetative filament . Under favorable conditions, fragmentation is the most common method of reproduction in Spirogyra . The breakdown of the filament to form individual fragments might occur either due to mechanical injury, dissolution of the middle lamella, or the formation of H-shaped fragments .

Asexual reproduction

Asexual reproduction is less common among Spirogyra, but it occurs in some species under unfavorable conditions by means of the formation of asexual spores like aplanospores, akinetes, and zygospores .

• Aplanospores are formed under unfavorable conditions where the cytoplasm of the cell shrinks and a wall is formed around it . The aplanospore is non-motile and eventually leads to the formation of a filament once the condition is favorable . In S. aplanospora, the formation of aplanospores is the only method of reproduction.
• Akinetes are formed when some species of Spirogyra develop a thick wall around themselves to protect themselves from unfavorable conditions . Once the condition becomes favorable, the akinete develops to form a filament. It is common in S. farlowii.
• Azygospores are formed when in S. varians, sometimes the gametes fail to fuse during sexual reproduction and get enclosed by a thick cell wall forming an azygospore. Like other asexual spores, azygospores also develops to form a new filament.

Sexual reproduction

Sexual reproduction in Spirogyra occurs via alternation between a haploid filament and a diploid zygospore. Conjugation is the method of sexual reproduction in Spirogyra where the fusion of two gametes of opposite strains takes place. The entire protoplasmic content of the cell acts as the gamete. The gametes are morphologically identical, but during conjugation, one of the gametes becomes active (male gamete) while the other becomes passive or non-motile.

Conjugation in Spirogyra is of two types; Scalariform and Lateral Conjugation

• Scalariform Conjugation: It is the more common mode of conjugation that occurs between two different filaments when they come close and lie parallel to each other. Then opposite cells develop protuberances or outgrowths that extend and come in contact with one another. The top of these outgrowths then dissolves to form a conjugation tube between the two cells. This results in the formation of a ladder-like structure (scalariform) throughout the filament. Meanwhile, the protoplasm of the cells round up to form gametes, and the motile male gamete then moves through the conjugation tube to reach the female gamete. 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 often and occurs between two adjacent cells of the same filament. It might occur in two further ways; Indirect and Direct lateral conjugation.

  • Indirect lateral conjugation: During indirect lateral conjugation, outgrowths emerge on the sides of the septum, which eventually leads to the formation of an opening at the lateral side of the cells. One of the two adjacent cells acts as male gametangia, whereas the other acts as the female gametangia. The male gamete then moves through the tube and fuses with the female gamete to form a zygote. In species reproducing by indirect lateral conjugation, in every second cell of the filament, a zygospore is formed. It occurs in tenuissima, S. affinis, etc.
  • Direct lateral conjugation: During direct lateral conjugation, a pore is formed in the septum that becomes big enough for the male gametangia to pass trough. The male gamete is then transferred through the pore into the female gametangia where they fuse to form a diploid zygote. It occurs in S .jogensis.
    
    Reproduction in Spirogyra: Vegetative, Asexual and Sexual reproduction
    

Spirogyra can reproduce by three methods: vegetative, asexual and sexual reproduction. The most common mode of reproduction is vegetative reproduction by fragmentation, which occurs under favorable conditions. Asexual reproduction is rare and occurs by the formation of spores in some species. Sexual reproduction occurs by conjugation, which involves the fusion of gametes from different filaments.

Vegetative reproduction

• Vegetative reproduction in Spirogyra takes place by fragmentation under favorable conditions.
• In fragmentation, the filament breaks at cross walls into one or more segments or fragments.
• Each fragment may consist of a few living cells or even a single cell and each fragment grows into a new filament by repeated cell division and growth.
• Fragmentation can be due to mechanical injury, dissolution of the middle lamella, or the formation of H-shaped fragments.

Asexual reproduction

• Asexual reproduction is less common among Spirogyra and occurs in some species under unfavorable conditions by means of the formation of asexual spores like aplanospores, akinetes, and zygospores.
• Aplanospores are formed when the cytoplasm of the cell shrinks and a wall is formed around it. The aplanospore is non-motile and eventually leads to the formation of a filament once the condition is favorable. In S. aplanospora, the formation of aplanospores is the only method of reproduction.
• Akinetes are formed when the cell develops a thick wall around itself to protect itself from the unfavorable condition. Once the condition becomes favorable, the akinete develops to form a filament. It is common in S. farlowii.
• Zygospores are formed when the gametes fail to fuse during sexual reproduction and get enclosed by a thick cell wall forming an zygospore. Like other asexual spores, zygospores also develop to form a new filament. It occurs in S. varians.

Sexual reproduction

• Sexual reproduction in Spirogyra occurs via alternation between a haploid filament and a diploid zygospore.
• Conjugation is the method of sexual reproduction in Spirogyra where the fusion of two gametes of opposite strains takes place. The entire protoplasmic content of the cell acts as the gamete.
• The gametes are morphologically identical, but during conjugation, one of the gametes becomes active (male gamete) while the other becomes passive or non-motile (female gamete).
• Conjugation in Spirogyra is of two types; Scalariform and Lateral Conjugation.

Scalariform Conjugation

• It is the more common mode of conjugation that occurs between two different filaments when the two filaments come close and lie parallel to each other.
• Then the opposite cells develop protuberances or outgrowths that extend and come in contact with one another.
• The top of these outgrowths then dissolves to form a conjugation tube between the two cells.
• This results in the formation of a ladder-like structure (scalariform) throughout the filament.
• Meanwhile, the protoplasm of the cells round up to form gametes, and the motile male gamete then moves through the conjugation tube to reach the female gamete.
• 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 often and occurs between two adjacent cells of the same filament. It might occur in two further ways; Indirect and Direct lateral conjugation.

Indirect lateral conjugation

• During indirect lateral conjugation, outgrowths emerge on the sides of the septum, which eventually leads to the formation of an opening at the lateral side of the cells.
• One of the two adjacent cells acts as male gametangia, whereas the other acts as female gametangia.
• The male gamete then moves through the tube and fuses with female gamete to form a zygote.
• In species reproducing by indirect lateral conjugation, in every second cell of the filament, a zygospore is formed.
• It occurs in S. tenuissima, S. affinis, etc.

Direct lateral conjugation

• During direct lateral conjugation, a pore is formed in the septum that becomes big enough for the male gametangia to pass through.
• The male gamete is then transferred through the pore into the female gametangia where they fuse to form a diploid zygote.

• It occurs in S. jogensis.

  Identification of Spirogyra: Cultural and Molecular identification

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

Cultural identification

The 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), number of chloroplasts per cell, and number of turns of the chloroplast, and the type of the vegetative cells are some of the characteristics that can be used to distinguish different species.

Besides, species can also be identified based on the structure of the reproductive spores and the type of conjugation.

The size of the zygospore and the nature of the spore membrane are also studied to obtain proper identification.

Spirogyra can be cultured in different media such as BG-11 medium or Bold`s Basal Medium with triple nitrate and vitamins.

The growth characteristics, pigment composition, mucilage production, and biochemical properties of Spirogyra can also be used for cultural identification .

Molecular identification

For better and more detailed identification of the species, molecular identification methods can also be applied.

The most common method of identification of the organism using a molecular technique is DNA sequencing.

During DNA sequencing, the DNA is first extracted and purified, followed by amplification via PCR.

The purified PCR products can then be sequenced directly using various sequencing tools.

Based on the results from the molecular and molecular methods of identification, a molecular phylogeny of the species of Spirogyra can be prepared .

Molecular identification can also reveal the genetic diversity and evolutionary relationships among different species and genera of Spirogyra .

Molecular markers such as rbcL gene, ITS region, 18S rDNA gene, and trnL-F region can be used for molecular identification .

Molecular identification can also help to resolve some taxonomic uncertainties and controversies regarding some species and genera related to Spirogyra . For example, molecular analysis has shown that Sirogonium is part of a clade containing many species of Spirogyra, whereas Temnogyra might be a separate genus based on its unique morphology.

Some possible additional sentences to conclude are:

• Therefore, both cultural and molecular methods are useful for identifying Spirogyra species and understanding their diversity and evolution.

• In conclusion, Spirogyra is a diverse and complex genus that requires a combination of cultural and molecular methods for accurate identification and classification.

  Economic Importance / Applications / Uses of Spirogyra

Spirogyra is a green alga that has various economic importance, applications, and uses in different fields. Some of them are:

• Food source: Some species of Spirogyra are used as a source of food in different parts of the world as they are rich in vitamins and minerals . They are also eaten by fish and other aquatic animals.
• Aquatic ecosystem: Green algae like Spirogyra are also an important part of the aquatic ecosystems as they are photosynthetic and thus provide oxygen to other organisms in the water . They also help in maintaining the nutrient cycles and water quality in freshwater habitats.
• Bioactive compounds: Spirogyra is also considered as an essential source of various natural bioactive compounds that can be used for the antibiotic, antioxidant, and anti-inflammatory purposes. Some Spirogyra species have been found to have the potential for the treatment of cancer, liver lesions, and other diseases.
• Wastewater treatment and biofuel production: Some Spirogyra species have been found to have the potential for the treatment of municipal wastewater and biomass production for biofuel applications. They can remove pollutants like nitrogen, phosphorus, heavy metals, and organic matter from wastewater and produce biogas or biodiesel from their biomass.
• Fertilizer: Spirogyra can also be used as a fertilizer for crops as they contain nitrogen, phosphorus, potassium, and other minerals that can enhance soil fertility and crop yield. They can also improve soil structure and water retention capacity.

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