Microbio 3: Algae Protists

Algae: The Photosynthetic Protist

General Characteristics of Algae

• Overall Morphology: Algae exhibit diverse morphologies including unicellular, colonial, filamentous, clublike, spiral, and larger forms.
• Photosynthetic Autotrophs: Algae are protists that carry out photosynthesis.
• Eukaryotic Organelles: Algal cells contain all eukaryotic organelles.
• Polyphyletic: Algae do not share a single common ancestor.
• Motility: Many algae move via flagella or gliding. Some have light-sensitive areas (eye spots) that coordinate with flagella to guide them toward light for photosynthesis.
• Cell Walls: Algae have thick cell walls or a thick cell membrane called a pellicle.
• Phycocolloids: The cell walls of many seaweeds contain phycocolloids (algal colloids) extractable with hot water. The three major phycocolloids are:
  • Alginates
  • Agars
  • Carrageenans
• Size Range: Algae range in size from microscopic unicellular phytoplanktons to large multicellular seaweeds.
• Distribution: Algae are widespread in fresh and marine waters.
• Habitats: Algae inhabit surfaces of soil, rocks, and plants, and can even live in hot springs or snowbanks.
• Plankton: Algae are part of the plankton, a large floating community of microscopic organisms.
• Ecological Role: Algae play an essential role in the aquatic food web and produce most of the Earth's oxygen.

Algal Groups

• Classification: Microscopic algae are classified into divisions or kingdoms based on:
  • Types of chlorophyll and other pigments
  • Type of cell covering
  • Nature of stored foods
  • Genetic factors
• Common Names of Groups:
  • Green Algae (Chlorophyta)
  • Red Seaweeds (Rhodophyta)
  • Brown Algae (Phaeophyta)
  • Diatoms (Chrysophyta)
  • Dinoflagellates (Pyrrophyta)
  • Euglenids (Euglenophyta)

Green Algae (Chlorophyta)

• Large diversity in freshwater habitats.
• Present in marine habitats but less important than red and brown algae.
• Close evolutionary relationship to plants.
• Similar chemistry and morphology to plants.
• Various growth forms evolved from basic Chlamydomonas cell:
  • Chlamydomonas: unicellular
  • Ulothrix: filamentous
  • Pandorina: clump
  • Ulva: sheet
• Most restricted to freshwater and terrestrial environments.
• 7000 species; 10% are marine; many are unicellular.
• Distributed mainly in bays, estuaries, and isolated tidal pools.
• Land plants may have evolved directly from green algae.

Multi-cellular Green Algae

• Spirogyra:
  • Filamentous alga found in pond water.
  • Common names: water silk, mermaid's tresses, and blanket weed.
  • Reproduces through conjugation.
• Chara

Red Algae (Rhodophyta)

• Red pigments called phycobilins mask chlorophyll.
• Largest group of seaweeds, about 4000 species; mostly marine.
• Found in most shallow water marine environments.
• Filamentous red algae and flatter branches.
• Mostly marine.
• Cell walls contain gels.
• Coralline Red Algae:
  • Smooth or rough encrusting growth on rocks.
  • Warm-water coralline red algae actively involved in the formation of coral reefs.
  • Dead man's fingers extend from tropical to temperate waters.

Secondary Products of Red Algae

• Carrageenan:
  • Used for stabilizing chocolate milk, egg nog, ice cream, sherbets, instant puddings, frostings, creamed soups, etc.
  • Similar to agar but requires higher concentrations to form gels.
  • Made from Gigartina stellata, Chondrus crispus, and Eucheuma.
• Agar (or agar-agar):
  • Used in bacteriology and mycology as a stiffening agent in growth media.
  • Used as a stabilizer for emulsions and as a constituent of cosmetic skin preparations, ointments, and lotions.
  • Made from Gelidium, Gracilaria, Pterocladia, and Ahnfeltia.

Brown Algae (Phaeophyta)

• Phylum Heterokontophyta, Class Phaeophyta.
• Brown algae exhibit the most complexly differentiated thalli.
• Fucoxanthin dominates over chlorophyll.
• Primary producers on temperate and polar rocky coasts.
• Almost 1500 marine species.
• Include the largest and most complex seaweeds.
• Kelps:
  • Found in deeper water below the lowest tide level.
  • Great abundance in temperate and sub-polar latitudes, forming kelp beds or kelp forests.
  • Can grow at least 50 cm per day in optimal conditions, reaching 100 m.
  • Among the richest, most productive environments in the marine realm.
  • Giant kelp (Macrocystis pyrifera) is a good source of Algin.
• Algin (alginate or alginic acid):
  • Anionic polysaccharide distributed widely in the cell walls of brown algae.
  • Used as thickening agent in ice cream, toothpaste, shaving creams, hair sprays, and lotions.

Golden Brown Algae (Chrysophyta)

• 'Chryso' means 'color of gold'.
• Three types: yellow-green algae, golden brown algae, diatoms.
• Diatoms are most abundant and are found in seawater and freshwater habitats.
• Diatom shells are made of silica.
• Major food source for many aquatic organisms.
• Fossil diatom shells form thick deposits on the sea floor known as 'diatomaceous earth'.

Dinoflagellates - Fire Algae (Pyrrophyta)

• Phylum Pyrrophyta.
• Dinoflagellate means 'spinning swimmers'.
• Cellulose-containing armor plates give them a sculpted appearance.
• Most species are found in saltwater environments.
• Common cause of red tides - algal blooms.

Red Tide

• Dinoflagellates causing red tides are often Gonyaulax, which contain a neurotoxin and are poisonous to marine fauna.
• Worldwide occurrence.
• Caused by dinoflagellates and diatoms.

Harmful Algal Blooms (HABS)

• Most Harmful Algal Blooms occur in coastal areas where terrestrial runoff of nutrients causes the growth and proliferation of sometimes monospecific blooms of toxic algae.
• Algae that produce toxins: Dinoflagellates, Diatoms, and Cyanobacteria.
• Very potent toxins (few cells per liter can produce toxic effects).
• Toxic effects on organisms.
• Physical impairment of fish.
• Nuisance conditions from odors or discoloration of water or habitats.
• Red Tide: Caused by algae.
• Brown Tide: Caused by Chrysophyta (golden-brown algae).

Algae Associated with HABS

• Maitotoxin
• Aureococcus
• Aureoumbra

Toxic Dinoflagellate Blooms

• Ciguatera Fish Poisoning
• Diarrhetic Shellfish Poisoning
• Neurotoxic Shellfish Poisoning
• Paralytic Shellfish Poisoning

Toxic Diatom Blooms

• Amnesic Shellfish Poisoning

Harmful Blooms (non-toxic or toxicity not confirmed)

• Pfiesteria, Chaetoceros, Heterosigma
  • Fish kills
  • Brown tides
• Aureococcus, Aureoumbra

Ciguatera Fish Poisoning

• Gambierdiscus toxicus (a dinoflagellate).
• Associated with weeds and coral reefs.
• Optimum conditions: shallow waters, 25-34°C, 25-40 ppt.
• Toxins: Ciguatoxin and maitotoxin.
• Vectors: Usually large fish, bottom dwellers, and reef fish (e.g., Red snapper, Grouper, Amber Jack, Sturgeon).
• Ciguatoxin properties:
  • Bioaccumulates
  • Stable and heat resistant
  • Lipid soluble
  • Highly potent (clinical effects from < 1 mg)

Diarrhetic Shellfish Poisoning

• Dinoflagellates: Dinophysis acuminata, Dinophysis fortii, Prorocentrum lima.
• Toxins: Okadaic acids and dinophysistoxins.
• Human Symptoms:
  • Generally mild gastrointestinal illness
  • Diarrhea, nausea, vomiting
  • Rapid onset, rapid resolution
  • No neurotoxic effects
• FDA level in shellfish - 0.2 ppm okadaic acid plus 35-methyl-okadaic acid

Neurotoxic Shellfish Poisoning

• Karenia brevis (previously Gymnodinium breve).
• Florida, Gulf of Mexico.
• Toxins: Brevetoxins.
• Human Symptoms:
  • Similar to ciguatera poisoning.
  • Early symptoms: Gastrointestinal (nausea, diarrhea, vomiting).
  • Late symptoms: Neurological (tingling, numbness).
• Ecological Impacts:
  • Massive fish kills.
  • Harmful to birds (pelican, seagulls, cormorants) and manatees.
• FDA level in fish - 0.8 ppm brevitoxin-2 equivalent.

Paralytic Shellfish Poisoning

• Dinoflagellates:
  • Alexandrium spp.
  • Gymnodinium spp.
  • Pyrodinium spp.
• Northern Atlantic and Pacific coasts.
• Temperate and tropical.
• Toxins: Saxitoxins.
• Human Symptoms:
  • Rapid onset (~30 min).
  • Absence of gastrointestinal symptoms.
  • Neurological symptoms (numbness, headache).
  • Ataxia (the loss of full control of bodily movements).
  • Weakness.
  • Cranial nerve dysfunction.
  • Diaphragmatic paralysis.
  • Death by asphyxiation.
  • Weakness can persist for weeks.
• Therapy: Not available (supportive only).
• FDA limit in fish 0.8 ppm.

Amnesic Shellfish Poisoning

• Pseudo-nitzschia spp. (diatoms).
• Discovered in 1987 (Price Edward Isl., Canada).
• Toxins: Domoic acid and Glutamic acid.

Toxic Phytoplankton & Human poisoning

• Amnesic shellfish poisoning - domoic acid
• Cyanobacterial neurotoxins - anatoxins
• Cyanobacterial hepatotoxins - microcystin, nodularin
• Dermatitis lyngbyatoxin, aplysiatoxin
• Paralytic shellfish poisoning - saxitoxin
• Neurotoxic shellfish poisoning - brevetoxin
• Ciguatera fish poisoning - ciguatoxin and maitotoxin
• Diarrhetic shellfish poisoning - okadaic acid

EUGLENIDS (EUGLENOPHYTA)

• Unicellular organisms with flagella.
• Euglena possesses features of algae and protozoa.
• Algae feature: contains chloroplasts.
• Protozoan feature: presence of primitive mouth (cytosome) and the absence of cell wall.
• Presence also of flagella.
• Structurally, they do not have a cell wall. Instead, they have a thick outer covering, known as a pellicle, that is composed of protein and gives them both strength and flexibility.
• Chloroplasts within the euglena trap sunlight that is used for photosynthesis, and can be seen as several rod like structures throughout the cell.
• Euglena also have an eyespot (stigma) at the anterior end that detects light, it can be seen near the reservoir.

Protothecosis (Algaemia)

• A disease found in dogs, cats, cattle, and humans.
• Caused by a type of green alga known as Prototheca that lacks chlorophyll and enters the bloodstream.

Summary of Algal Characteristics

Important Characteristics of Seaweed and Marine Groups