Introduction to Algae

Harriet Wilson, Lecture Notes

Bio. Sci. 4 - Microbiology

Sierra College

Introduction to Algae

According to the Whittaker five-kingdom system of classification, single-celled algae and

protozoa belong to the Kingdom Protista. Although sometimes divided into other

kingdoms (including Chromista, Alveolata, Parabasala, etc.), the microscopic algae and

protozoa are frequently referred to as protists, and for the sack of simplicity will be left as

protista here. The lecture information for algae and protozoa will be presented in two

parts with algae described first.

Microscopic algae (singular = alga) are plant-like organisms occurring as single cells,

thread-like filaments, or colonies of various shapes and composition. They are abundant

in water (both fresh and marine), in damp soil and on moist surfaces. Some types of algae

live inside other organisms and some form symbiotic relationships with fungi in structures

called lichens.

Phycology – The science or study of algae is called phycology (phykos = sea weed), and

initially involved the investigation of macroscopic organisms common in marine habitats.

Many types of marine algae are macroscopic, sometimes reaching nearly 100 feet in length,

but since this is a microbiology course, those organisms are not included here.

Algae are oxygenic photoautotrophs and contain green-colored pigments called

chlorophylls within folded membranous thylakoids of organelles called chloroplasts

(recall eukaryotic cell structure and function). The green chlorophyll pigments are light-

sensitive and allow algae to convert light energy into chemical energy (ATP) through a

process called photophosphorylation. Algae produce oxygen (are oxygenic) by splitting

water molecules and are sometimes credited with producing up to 70% of the oxygen

present in the earth's atmosphere (though reaching this percentage probably requires the

inclusion of oxygen produced by cyanobacteria as well). As autotrophs, algae take in

inorganic carbon (carbon dioxide) from the atmosphere and use it to form organic

compounds (sugars) that can be metabolized in a variety of ways. They are self-feeding,

but also provide food for other organisms. Algae are ecologically categorized as

producers and play an essential role at the bottom of multiple food chains (webs).

Algae cells, like those of fungi, are surrounded by rigid, non-living layers called cell walls.

Most algae have walls made of polysaccharide (cellulose or agar), but some contain

quantities of glass (silica dioxide). Walls give algae cells their characteristic shape and

allow them to live in hyportonic environments without being damaged. Though plant-like

in some ways, algae do not have stems, leaves or roots. The body of a multicellular alga is

called a thallus and may have structures resembling stems, leaves and roots. Single-celled,

filamentous, and colonial forms of algae are much simpler in composition.

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Harriet Wilson, Lecture Notes Bio. Sci. 4 - Microbiology Sierra College

According to the Whittaker five-kingdom system of classification, single-celled algae and protozoa belong to the Kingdom Protista. Although sometimes divided into other kingdoms (including Chromista, Alveolata, Parabasala, etc.), the microscopic algae and protozoa are frequently referred to as protists, and for the sack of simplicity will be left as protista here. The lecture information for algae and protozoa will be presented in two parts with algae described first. Microscopic algae (singular = alga) are plant-like organisms occurring as single cells, thread-like filaments, or colonies of various shapes and composition. They are abundant in water (both fresh and marine), in damp soil and on moist surfaces. Some types of algae live inside other organisms and some form symbiotic relationships with fungi in structures called lichens. Phycology – The science or study of algae is called phycology (phykos = sea weed), and initially involved the investigation of macroscopic organisms common in marine habitats. Many types of marine algae are macroscopic, sometimes reaching nearly 100 feet in length, but since this is a microbiology course, those organisms are not included here. Algae are oxygenic photoautotrophs and contain green-colored pigments called chlorophylls within folded membranous thylakoids of organelles called chloroplasts (recall eukaryotic cell structure and function). The green chlorophyll pigments are light- sensitive and allow algae to convert light energy into chemical energy (ATP) through a process called photophosphorylation. Algae produce oxygen (are oxygenic) by splitting water molecules and are sometimes credited with producing up to 70% of the oxygen present in the earth's atmosphere (though reaching this percentage probably requires the inclusion of oxygen produced by cyanobacteria as well). As autotrophs , algae take in inorganic carbon (carbon dioxide) from the atmosphere and use it to form organic compounds (sugars) that can be metabolized in a variety of ways. They are self-feeding, but also provide food for other organisms. Algae are ecologically categorized as producers and play an essential role at the bottom of multiple food chains (webs). Algae cells, like those of fungi, are surrounded by rigid, non-living layers called cell walls. Most algae have walls made of polysaccharide (cellulose or agar), but some contain quantities of glass (silica dioxide). Walls give algae cells their characteristic shape and allow them to live in hyportonic environments without being damaged. Though plant-like in some ways, algae do not have stems, leaves or roots. The body of a multicellular alga is called a thallus and may have structures resembling stems, leaves and roots. Single-celled, filamentous, and colonial forms of algae are much simpler in composition.

Algae Reproduction Algae reproduce both sexually and asexually, with asexual reproduction occurring more commonly. Some variation in asexual reproduction are described below. a) Fission – Fission in algae (like fission in other cells) involves mitosis (the separation of chromosomes) and cytokinesis (the division of the protoplasm into two parts). Some algae, such as Spirogyra and Oedogonium , undergo binary fission , i.e., divide in half across their long axis. Other types, such as Chlamydomonas , undergo longitudinal fission , i.e., divide in half lengthwise. b) Shrinking division – Asexual reproduction in diatoms involves a specialized type of fission called "shrinking division" which results in the formation of two cells of unequal size. Diatoms have glass walls composed of two parts called frustules or valves (depending on sources) that fit together like the two sections (lid and bottom) of a Petri plate. When a diatom undergoes fission, the two wall sections separate, and a new wall is formed on the inside of each. The diatom receiving the "lid" section of wall will be the same sized as the original cell, but the one receiving the "bottom" will be smaller. Repeating fission cycles will produce smaller and smaller diatoms until a minimum size is reached, and then stops. This explains the size variation typical of diatoms in the same species. Sometimes produce asexual spores. c) Fragmentation – Filamentous forms of algae can undergo fragmentation (like fungus hyphae), and each fragment can grow into a new filament. d) Spore formation – Algae, like fungi, produce asexual spores of various types. Sexual Reproduction Sexual reproduction as it occurs in algae is similar to that occurring in fungi in that it involves three stages or steps called plasmogamy , karyogamy and meiosis. This similarity is largely due to historical events, i.e., algae and fungi were both considered members of the kingdom Plantae, and the reproductive processes of both groups were described by botanists. Sexual reproduction requires the participation of two genetically dissimilar algae (of the same species) and typically occurs in three stages or steps as outlined below:

Plasmogamy – Plasmogamy involves the joining of the protoplasm (plasma = protoplasm, gamous = union or marriage), and requires decomposition of the cell walls separating the cells involved.
Karyogamy – Karyogamy involves the joining of two haploid nuclei (karyon = nucleus) and results in the formation of a diploid cell called a zygote. Haploid cells/nuclei have only one set of chromosomes, while diploid cells/nuclei have two.
Meiosis – Meiosis (reduction division) is a process involving separation of chromosomes and the division of the diploid nucleus into two, haploid parts. An important feature of meiosis is the formation of new genetic combinations, not possible through asexual reproduction. These stages may be separated in time, and result in the formation of two separate generations of algae known as sporophytes and gametophytes. The gametophyte generation is composed of haploid cells that can undergo plasmogamy and karyogamy to form diploid zygotes. The diploid cells form the sporophyte generation , and these can undergo meiosis to form gametophytes. Since cells of the gametophyte and sporophyte

(formerly Gonyaulax ) and Gymnodinium are commonly associated with PSP. Though multiple factors may influence eutrophication, "red tides" are most common along California's northern coast during months without the letter "r" in them.

Pfiesteria threatens both fish and fishermen. Dinoflagellates identified as Pfiesteria piscicida cause considerable damage along the eastern coast of the US by attacking and killing fish in large numbers. Though the fish being killed by these dinoflagellates are small in size, they are important to the fishing industry because they feed other, larger fish of commercial interest. Pfiesteria also produce neurotoxins that are harmful to humans, causing neurological symptoms such as headache, dizziness and memory loss. When present in high concentrations, these toxins may become airborne and cause damage to people not contacting contaminated fish or water.
Some dinoflagellates are bioluminescent. Dinoflagellates in the genus Noctiluca carry lux genes and produce luciferase enzymes involved in converting chemical energy into light energy. Like bioluminescent bacteria, these dinoflagellates produce their own light, or glow in the dark. During red tides, Noctiluca can cause waves to light up as they break on the shore, sand to sparkle under foot, and ships to leave light trails as they travel through the water.
Diatom cell walls form diatomaceous earth. Diatoms, microscopic algae with glass cell walls, are often abundant in both fresh and salt water. During earlier periods in the earth's history, diatoms inhabited inland seas that are no longer present. Their cell walls accumulated at the sea bottom, forming a sedimentary rock type called diatomite. This material now occurs as deposits on dry land and can be "mined" and ground into diatomaceous earth. Diatomaceous earth is used extensively in filters for water, honey, apple juice and other liquids. It is also used as an abrasive in car polish, toothpaste and cleansers. Diatoms have clinical significance because diatomaceous earth can be used to determine blood clotting time. Some diatoms produce a neurotoxin called domoic acid that can cause damage to humans eating seafood that was formerly feeding on diatoms.
Red algae make agar. Agar, the polysaccharide commonly used as a solidifying agent in microbiological media is made by red algae (Phylum Rhodophyta). Algae and symbiotic relationships Endophytic – The term endophytic applies to algae living inside other organisms. Though green chlorophyll pigments occur in nearly all types of algae, green-colored protista are not necessarily algae. Sometimes algae live inside other organisms, causing them to appear green. Since algae are photoautotrophs, they cannot be considered as parasites, so when they live inside another organism they are said to be endophytic. Endophytic algae can be found living inside organisms such as sea anemones, Hydra , flatworms, sponges and several types of protozoa. Lichens – Lichens are organisms made up of algae (or cyanobacteria) and fungi living together symbiotically. Though classified as individual organisms, lichens are actually

composed of two different types of organisms living together. The relationship between fungus and alga cells is mutualistic, with the algae providing food through photosynthesis (by collecting and processing carbon dioxide) and the fungi providing protection and metabolic water. Lichens are extremely hardy, often colonizing environments where few other organisms can grow (e.g., on rock surfaces). Sometimes they are the first organisms to return after a fire or volcano removes all vegetation.

Introduction to Algae - Microbiology | BIOL 0004, Study notes of Microbiology

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Introduction to Algae