Introduction to Algae

What are Algae?

• Algae are eukaryotic, photosynthetic lifeforms
• Can be found in oceans, rivers, lakes, ponds, brackish waters, and even snow
• Algae are chlorophyll-containing thalloid plants
• They lack true roots, stems, leaves, or leaflike organs
• Algae are classified under the Division Thallophyta
• Algae differ from fungi due to the presence of chlorophyll and their mode of nutrition
• Most algae are autotrophic; able to make their own food

Occurrence

• Algae habitats include freshwater, seawater, snow, rocks, and on or inside plant and animal bodies
• Algae are classified into three groups based on habitat
  • Aquatic
  • Terrestrial
  • Unusual

Aquatic Algae

• Aquatic algae are found in freshwater or saline water
• Freshwater forms examples include Cladophora, Oedogonium, Ulothrix, Volvox, and Spirogyra
• Marine forms are found in saline water
  • Phaeophyceae (Ectocarpus, Sargassum, Fucus)
  • Rhodophyceae (Polysiphonia)
• Types of aquatic algae:
  • Free-floating: Chlamydomonas, Volvox, Spirogyra
  • Holdfast: Attached to a substratum via an attachment disc
    • Examples: Oedogonium, Ulothrix
  • Phytoplanktons: Free-floating colonies on the water surface
    • Euplanktophytes: Never attached and free-floating from the start
      • Examples: Diatoms, Cosmarium, Chlamydomonas, Volvox
    • Tychoplanktophytes: Initially attached but later become detached and free-floating
      • Examples: Spirogyra, Zygnema, Cladophora, Oedogonium, Microspora, Tetraspora, Rivularia, and Nostoc

Terrestrial Algae

• Terrestrial Algae are also known as Edaphophytes
• Found on or inside the surface of the earth
• Saphophytes: On the surface of the soil
  • Examples: Vaucheria, Protosiphon
• Cryptophytes: Live below the surface of the soil
  • Examples: Nostoc, Anabaena

Algae of Unusual Habitats

• Halophytic Algae: Live in salt lakes at high salt concentrations
  • Examples: Chlamydomonas, Dunaliella, Stephanoptera
• Epiphytic Algae: Grows on larger algae, bryophytes, or angiosperms
  • Coleochaete species on grasses near ponds are an example
• Epizoic Algae: Grows on living aquatic animals like snails, fishes, and tortoises
  • Cladophora crispata on snails and Stigeoclonium in fish gills are examples
• Endozoic Algae: Occurs within animal tissues
  • Zoochlorella in Hydra viridis is an example
  • Several Oscillatoriaceae species exsist in vertebrate respiratory and digestive tracts
• Symbiotic Algae: Forms symbiotic associations with fungi, bryophytes, gymnosperms, and angiosperms
  • Lichens are examples of this
  • Algal components: Cyanophyceae(Nostoc, Gloeocapsa, Microcystis) or Chlorophyceae (Соссотуха, Chlorella, Protococcus)
• Cryophytic Algae: Grows on ice or snow, coloring snow-covered mountains
  • Alpine and arctic mountains turn red with Haematococcus nivalis, Gloeocapsa, diatoms
  • Green snow in Europe is caused by Chlamydomonas yellowstonensis and Mesotaenium species
  • Black snow results from Scotiella nivalis and Raphidonema brevirostri
  • Brownish-purple snow caused from Ancyclonema nordenskioldii
• Lithophytic Algae: Grow on moist rocks and stones
  • Blue-green algae like Nostoc, Rivularia, and Gloeocapsa on moist, shady rocks
  • Scytonema can be found on moist walls during the rainy season
• Parasitic Algae: Grow as parasites on plants and animals
  • Chlorophyceae causes red rust in tea and coffee plantations
• Thermophytes (Thermal Algae): Found in hot water springs (50-70°C)
  • Examples: Oscillatoria brevis, Heterohormogonium sp
  • Survive high temperatures due to the absence of a well-organized nucleus
  • Copeland noted 153 Chroococcaeae species can survive up to 84°C; some Oscillatoriaceae up to 85°C

Cell Structure in Algae

• Cell Wall
• Flagella
• Nucleus
• Golgi Bodies or Dictyosomes
• Mitochondria
• Endoplasmic Reticulum
• Eye Spot- Stigma
• Vacuoles
• Gas Vacuoles
• Pigments
• Pyrenoids

Cell Wall

• Composed of pure or mixed carbohydrates (cellulose, mucilage, pectin)
• Substances like alginic acid, fucoidin, fucin, and hemicelluloses are present in brown algae (Phaeophyceae), pectin in red algae (Rhodophyceae), calcium carbonate in coralline algae (red algae), and silica in diatoms (Bacillariophyceae)

Flagella

• Motile vegetative or reproductive cells are in all algal groups except Cyanophyceae and Rhodophyceae
• Small, thread-like protoplasmic appendages
• Two main types:
• Whiplash or Acronematic Flagella: Smooth surface
• Tinsel or Pleuronematic Flagella: Surface covered with mastigonemes or flimmers
• A motile cell may have one or two types of flagella

Nucleus

• A well-organized eukaryotic nucleus
• Size ranges from less than 1 µm to 80 µm
• Two-layered nuclear membrane with a perinuclear space
• Contains one or more dark-stained nucleoli or endosomes
• Four types of nucleolar structures
  • A single nucleolus per nucleus
  • Two or more distinct nucleoli per nucleus
  • A complex nucleolar mass
  • A linear association of many small nucleoli
• Chromosome number varies
  • Lowest: n = 2 in Porphyra linearis (Rhodophyceae)
  • Highest: n = 592 in Netrium digitalis (Chlorophyceae)

Golgi Bodies or Dictyosomes

• Present in all algal cells except blue-green algae
• Composed of 2-20 flat vesicles arranged in stacks
• Each stack is called a dictyosome (collectively forming the Golgi apparatus)
• Associated with synthesizing cell metabolites and contributing to the plasma membrane

Mitochondria

• Well-organized mitochondria in all algal cells except blue-green algae
• Bounded by a double membrane
• Inner membrane projects into the lumen, forming finger-like projections called cristae
• Lumen filled with a granular matrix containing nucleic acids (RNA and DNA)
• Respiratory enzymes are located in mitochondria, making them respiratory centers
• Sites of enzyme action in protein synthesis and amino acid interconversions

Endoplasmic Reticulum (ER)

• A system of interconnecting tubules traverses the cytoplasm of algal cells
• The surface of ER is studded with ribosomes, which are the sites of protein synthesis in the cell

Eye-spot or Stigma

• A pigmented spot in motile vegetative and reproductive cells
• There are five types based on position and structure:

Vacuoles

• Mature cells of almost all classes of algae possess one or more vacuoles, except Cyanophyceae
• Bounded by a distinct membrane called tonoplast
• There are two types in motile algal cells
  • Simple or Contractile Vacuoles
  • Complex Vacuoles: Found in Chlorophyceae; has a tube-like cytopharynx
• Vacuoles perform osmoregulation and help regulate water/solute absorption

Gas Vacuoles

• Gas-containing cavities are characteristic of mature healthy Cyanophyceae cells
• They occur as stacks of small transparent cylinders of uniform diameter
• Walls are freely permeable to gases

Pigments

• Algal cells have characteristic colors due to specific pigment combinations
• In all classes except Cyanophyceae, pigments are present within membrane-bound organelles called plastids
• In blue-greens, pigments are concentrated in the peripheral cytoplasm and known as chromoplasm
• Two types of plastids:
  • Leucoplast: Colorless plastids
  • Chromoplast: Colored plastids
    • Chloroplasts: Contain chlorophyll a and chlorophyll b
    • Chromatophores: Lack chlorophyll a and chlorophyll b
• Types of pigments:
  • Chlorophyll: There are five types: chl a, b, c, d, and e
  • Xanthophyll: There are more than 20 types; formed by incorporating molecular oxygen into carotene molecules, fucoxanthin is the main xanthophyll
  • Carotenes: Oxygen-free alicyclic compounds composed of isoprene units with five types: A-carotene, B-carotene, C-carotene, D-carotene & E-carotene
  • Phycobilins: These are water-soluble complexes containing protein and bile pigments and are present in photosynthetic tissue
    • Red (phycoerythrin) and blue (phycocyanin) pigments
    • Light-harvesting pigments, transferring absorbed light to chlorophyll a

Pyrenoids

• Proteinaceous bodies present in chromatophores
• Used for the synthesis and storage of starch
• A chromatophore may have one or more pyrenoids
• Serve as transient structures associated with photosynthetic activity and stored food availability

Reproduction

• Propagation in algae happens through:
  • Vegetative
  • Asexual
  • Sexual

Vegetative Reproduction

• Cell Division or Fission: Simplest method
  • Found in unicellular algae like Chlamydomonas, desmids, and diatoms
  • Unicellular alga divides mitotically into two daughter cells, which then grow into independent organisms
• Fragmentation:
  • The thallus breaks into small fragments in filamentous forms
  • Each fragment can grow independently, forming a new thallus
  • Vegetative propagation by fragmentation of larger colonies occurs in colonial blue-green algae species like Spirogyra
• Budding: Bud-like structures form due to vesicle proliferation
  • A new organism develops from an outgrowth or "bud" on the parent algae
  • The bud detaches making it an independent organism
  • Allows rapid production of genetically identical offspring in species like Protosiphon

Asexual Reproduction

• Zoospores:
  • Motile, naked structures with two (Chlamydomonas, Ectocarpus), four (Ulothrix), or many (Oedogonium, Vaucheria) flagella
  • The zoospore has a bit of chloroplast and typically an eye spot
  • The cell creating the zoospore is the zoosporangium
  • The protoplast of zoosporangium forms a single zoospore or undergoes repeated divisions
  • Zoospores can be haploid or diploid
• Aplanospores: Non-motile spores
  • Commonly found in terrestrial algae; some aquatic algae (Ulothrix, Microspora) also make it during drought
  • Have a distinct wall, but no flagella
  • Each cell may form a single aplanospore, or its protoplast may divide to form many aplanospores
• Hypnospores: Some algae secrete thick walls to overcome prolonged desiccation
  • Such thick-walled spores are called hypnospores
  • Under favorable conditions, hypnospores germinate and new individuals or their protoplast may form zoospores
  • Chlamydomonas nivalis hypnospores are red due to haematochrome deposition
  • Examples: Pediastrum and Sphaerella
• Tetraspores: Non-motile spores
  • Formed within tetrasporangium by meiosis and are haploid
  • Germinate to form a haploid organism
• Autospores: Aplanospores with a similar structure to the parent cell
  • Acquire all features of the parent cell before liberation from the sporangium
  • Replicas of the parent cell that are smaller than the parent
  • Example: Chlorella
• Akinetes: Vegetative cells develop into thick-walled, spore-like structures with abundant food reserves
  • Akinetes always have additional wall layers around the protoplast and they fuse with the parent wall
  • Resistant to unfavorable environmental conditions
  • Found in many blue-green and green algae
• Exospores & Endospores: protoplast divides to form special non-motile spores in many blue-green algae.
  • The cell creating endospores enlarges and its contents divide successively, forming endospores (e.g., Dermocarpa)
  • Exospores are formed externally, with the cell protoplast coming out through a terminal pore and successively cutting spherical spores (e.g., Chamaesiphon)

Sexual Reproduction

• Autogamy:
  • Two gametes of the same mother cell fuse to form a diploid nucleus
  • Only karyogamy (fusion of two gametic nuclei) occurs
  • Forms a diploid zygote without any genetic variation
  • Common example: Diatoms
• Hologamy:
  • Unicellular forms, such as Chlamydomonas and Dunaliella, use vegetative cells of different strains (+) and (-) as gametes which fuse to form a zygote
  • Evolutionarily more advanced than autogamy due to the fusion of cells with different genetic constitutions
• Isogamy:
• Two gametes being morphologically and physiologically similar fuse to form a zygote
• Gametes are called isogametes, indistinguishable into plus and minus strains
• Gametes are motile and flagellate
• Found in algae like Ulothrix and Chlamydomonas eugametos
• Anisogamy:
• Fusion between morphologically and physiologically distinct gametes called anisogametes
• Male (microgametes) are smaller and more active while female (macrogametes) are larger and sluggish
• Found in many examples like Chlamydomonas braunii and Pandorina
• Oogamy:
  • An advanced type of sexual reproduction
  • A large, non-motile egg or ovum fuses with a small, motile sperm or antherozoid that are non-motile Rhodophyceae
  • Egg forms within the oogonium and sperms within the antheridium
• Examples: Volvox, Oedogonium, Chara, Vaucheria, Sargassum, Batrachospermum, and Polysiphonia

Thallus Structure

• Ranges from unicellular to multicellular
• Size ranges from one to several microns
• Five groups:
• Unicellular
• Colonial
• Filamentous
• Siphonaceous
• Parenchymatous

Unicellular Forms

• Simple unicellular forms are found in all groups of algae, except Charophyceae and Phaeophyceae
• Classified into four subgroups:
• Rhizopodial unicells
• Flagellated unicells
• Spiral filamentous unicells
• Non-motile coccoidal unicells

Rhizopodial Unicells

• Lack a rigid cell wall and contain a naked protoplast
• Have a soft periplasmic cell envelope, allowing extensive shape and size changes
• Use cytoplasmic projections called Pseudopodia and Rhizopoda for ameboid movement instead of flagella
• Examples: Chrysamoeba (Chrysophyceae), Rhizochloris (Xanthophyceae), and Dinophyceae

Flagellated Unicells

• Resemble motile gametes and zoospores
• Can be spherical, elongate, ovoid, or round in cross-section
• They contain one, two, or more flagella of equal or unequal length, and can be tinsel or whiplash-type
• Are present in almost all algal groups except Myxophyceae, Phaeophyceae, and Rhodophyceae

Spiral Filamentous Unicells

• Form spiral coiled structures
• Example: Spirulina

Non-motile Cocciodal Unicells

• Lack flagella and eye spots for locomotion
• Rigid cell walls
• Lack motility but can be motile during reproductive stages
• Examples: Prochloron, Aphanocapsa, and Synechococcus

Colonial Forms

• The colonial habit is achieved by aggregation of cell division products within a mucilaginous mass, aggregation of motile cells, or juxtaposition of cells after divisions
• All colony members have a similar structure
• These associations are loose and a colony may break into smaller pieces
• All members are connected by cytoplasmic connections, which means they cannot break into segments (e.g., Volvox)
• Colonial organization is divided into four types:
  • Coenobial
  • Palmelloid
  • Dendroid
  • Rhizopodial

Coenobial

• A colony with a definite shape, size, and arrangement of cells
• The number of cells is determined at the juvenile stage, and colony increases only in size
• Can be motile or non-motile; motile coenobia have flagellated cells (e.g., Pandorina, Eudorina, Volvox), while non-motile ones lack flagella (e.g., Hydrodictyon)

Palmelloid

• The cells have an indefinite number, shape, and size
• Cells remain irregularly aggregated within a common mucilaginous matrix but are independent and function as individuals
• Can be a temporary phase (e.g., Chlamydomonas) or a permanent feature (e.g., Tetraspora, Aphanotheca)

Dendroid

• Colony resembles a microscopic tree
• The cells have an indefinite, unique number, shape, and size
• Forms a branched structure, giving the colony a tree-like appearance (e.g., Chrysodendron)

Rhizopodial

• Cells are united through rhizopodia (e.g., Chrysidiastrum)

Filamentous Forms

• Daughter cells do not separate and remain attached, forming a filament.
• Filaments may be branched or unbranched, and the cells may be in a single row (uniaxial) or multiple rows (multiaxial)
• Simple unbranched filaments are found in only a few groups of algae
• Filaments may be free-floating (e.g., Spirogyra), attached to a substratum (e.g., Zygnema, Ulothrix, Oedogonium), or form a colony (e.g., Nostoc, Oscillatoria)

Branched Filaments

• Branched filaments are formed by repeated transverse divisions of lateral outgrowths of cells
• Branching can be false or true.
• False branches emerge from the mucilaginous sheath, e.g., Scytonema
• True branches arise as lateral outgrowths, resulting in three types of filaments:
• Simple Branches Simple filaments that are branched
  • Remain attached to the substratum by a basal cell
  • Branches can arise from any cell except the basal cell
  • In Cladophora, branches arise just below the septa between adjacent cells
• Heterotrichous Thallus: is highly evolved and differentiated into prostrate and erect systems (e.g., Fritschiella, Ectocarpus, Draparnaldiopsis, Coleochaete, Stigeoclonium
  • Both prostrate and erect systems may be well developed or there may be progressive elimination of either the prostrate (e.g., Draparnaldiopsis) or erect (e.g., Coleochaete) system
• Pseudoparenchymatous:One or more central or axial filaments, together with their branches, to form a 'parenchymatous' structure
  • If formed by the branches of only one filament, it is called uniaxial (e.g., Batrachospermum); if formed by branches of more than one filament, it is multiaxial (e.g., Polysiphonia)

Siphonaceous Forms

• Thallus consists of branched, aseptate, coenocytic, tubular filaments as nuclear divisions that are not accompanied by wall formation
• Examples: Vaucheria and Botrydium

Parenchymatous Forms

• Flat foliose or tubular thalli are formed by cell divisions in two or more planes
• Daughter cells do not separate, giving rise to parenchymatous thalli of different shapes, like flat (Ulva), tubular (Scytosiphon), or complex (Sargassum)
• Growth can be apical (e.g., Fucus, Dictyota), intercalary (e.g., Laminaria), or trichothallic (e.g., Porphyra)

Algal Classification and Distribution

• Carolus Linnaeus included algae with lichens and did not elaborate
• Vaucher proposed a classification of algae
• The three groups proposed by Vaucher are Conferves, Ulves, Thremelles
• Link classified algae based on the color of pigment and structure
• Harvey classified algae based on the color of pigment and habitat
• J.G Agardh divided algae into six classes: Diatomaceae, Nostochineae, Confervoideae, Ulvaceae, Floridae, Fucoideae
• Eichler grouped algae, along with fungi, under the division Thallophyta
• Engler & Prantle revised the classification of algae and included both algae and fungi and came up with the Scheme:

1. Schizophyta
2. Flagellata
3. Bacillariophyta
4. Chlorophyceae
5. Phaeophyceae
6. Eumycetes (Fungi)
7. Phytosarcodina
8. Dinoflagellata
9. Conjugatae
10. Charophyta
11. Rhodophyceae

• West divided algae into four categories based on reproductive structures and the presence or absence of flagella
• proposed a classification based on phylogeny, classified algae into eight divisions, and further subdivided into different classes, and inter-relationships among various groups
• Tilden classified algae into five classes based on reserve the food material, pigmentation, and flagellation
• Fritsch provided the most authentic and comprehensive account of algal classification, used pigments in the plastids, the number and point of flagella insertion in motile calls, chemical nature of reserve food material.and the presence or absence of an organized nucleus for the criteria:

Fritsch algae divisions

1. Chlorophyceae
2. Xanthophyceae
3. Chrysophyceae
4. Bacillariophyceae
5. Cryptophyceae
6. Dinophyceae
7. Chloromonadineae
8. Euglenophyceae
9. Phaeophyceae
10. Rhodophyceae
11. Myxophyceae

• A classification scheme:

• Class I: Chlorophyceae (Green Algae)
• Class II: Xanthophyceae (Yellow-Green)
• Class III: Chrysophyceae (Orange Algae)
• Class IV: Bacillariophyceae (Diatoms/Yellow or Golden Brown Algae)
• Class V: Cryptophyceae (Nearly Brown)
• Class VI: Dinophyceae (Dark Yellow or Brown)
• Class VII: Chloromonadinae (Bright Green)
• Class VIII: Euglenophyceae
• Class IX: Phaeophyceae (Brown Algae)
• Class X: Rhodophyceae (Red Algae)
• Class XI: Myxophyceae (Blue Green Algae)

Media for Cultivation of Algae

• Cultivation is the technique of growing algae in an artificial medium
• It supports the study of morphology and reproduction, life cycle phases, morphological, reproductive, ultrastructural characteristics, physiology, biochemistry, genetics, the rate of algae productivity, chemical composition, algicides effects, and relationships with water quality

Culture Media for Freshwater & Soil Algae

• Chu No. 10 (Modified) medium is suited for many freshwater and soil algae
• The main ingredients of it are:

Allen and Arnon's (Modified) Medium:

• Most suitable for nitrogen-fixing blue-green algae
• Adding Calcium Nitrate [Ca(NO3)2] makes it suited for non-nitrogen-fixing blue-green algae
  • The main ingredients of the medium are:

Chu No. 10 Medium

• Main ingredients of the medium are:

• M-1 Medium
• Most for freshwater planktonic green algae has ingredients:

Rodhe Medium (1948)

• Used for Diatoms & Green Algae, (stock solutions)

• Proportions added to one liter of water or nutrient medium:

Gerloff, Fitzgerald, and Skoog Medium (1950)

• Suitable for blue-green algae
  • Its main ingredients are:

McLaughlin, et al. Medium (1959)

• is suitable for Dinoflagellates and requires main Ingredients:

Culture Medium for Marine Algae

• The media solidified with 1% agar. Liquid culture has a small volume and the mineral salts' medium is taken in an Erlenmeyer flask or in a test tube
• Ingredients include:

Culturing of Algae

• Used to culture