12. Algae, Protozoa, and Slime Molds

• Algae


  Familiar as the large brown kelp in coastal waters, the green scum in a puddle, and the green stains on soil or on rocks
• A few algae are responsible for food poisonings
• Forms of algae


  • Unicellular
  • Chains of cells (filamentous)
  • Thalli

  
• Phycology


  The branch of microbiology that deals with the study of algae
• Algae


  Photoautotrophs that lack the roots and stems of plants
• Historically algae were considered plants, but they lack the embryos of true plants
• Algae


  Currently grouped into super clades
• Habitats of algae


  • Aquatic
  • Soil
  • On trees
• Unusual algal habitats include the hair of both the sedentary South American sloth and the polar bear
• Water is necessary for physical support, reproduction, and the diffusion of nutrients for algae
• Generally, algae are found in cool temperate waters
• The large floating mats of the brown alga Sargassum are found in the subtropical Sargasso Sea
• Some species of brown algae grow in antarctic waters
• General features of algae

  • Relatively simple eukaryotic phototrophs lacking tissues of plants
  • Identification of unicellular and filamentous algae requires microscopic examination
  • Most algae are found in the ocean
  • Their locations depend on the availability of appropriate nutrients, wavelengths of light, and surfaces on which they can grow

  
• Thallus


  The body of a multicellular alga
• Thalli of larger multicellular algae (seaweeds)

  • Branched holdfasts (which anchor the alga to a rock)
  • Stemlike and often hollow stipes
  • Leaflike blades
• The cells covering the thallus can carry out photosynthesis
• Thallus


  • Lacks the conductive tissue (xylem and phloem) characteristic of vascular plants
  • Absorbs nutrients from the water over their entire surface
  • The stipe is not lignified or woody, not offering support
  • The surrounding water supports the algal thallus
  • Some algae are also buoyed by a floating, gas-filled bladder called a pneumatocyst
• Asexual reproduction in algae

  1. Multicellular algae with thalli and filamentous forms can fragment; each piece can form a new thallus or filament

  2. When a unicellular alga divides, its nucleus divides (mitosis), and the two nuclei move to opposite parts of the cell. The cell then divides into two complete cells (cytokinesis)
• Sexual reproduction in algae

  1. Asexual reproduction may occur for several generations and then, under different conditions, the same species reproduce sexually

  2. Other species alternate generations so that the offspring resulting from sexual reproduction reproduce asexually, and the next generation then reproduces sexually
• Oomycotes


  Fungal-like algae that are chemoheterotrophs

  
• Photosynthetic algae are found throughout the photic (light) zone of bodies of water
• Chlorophyll a (a light-trapping pigment) and accessory pigments involved in photosynthesis are responsible for the distinctive colors of many algae
• Algae are classified according to their rRNA sequences, structures, pigments, and other qualities
• Phylum Phaeophyta (brown algae or kelp)


  • Macroscopic with some reaching lengths of 50 m
  • Mostly found in coastal waters with phenomenal growth rate with some exceeding 20 cm/day growth rate and therefore can be harvested regularly
• Algin


  Can be extracted from the cell walls of brown algae and used as a thickener in many foods such as ice cream and cake decorations, and in the production of rubber tires and hand lotions
• Laminaria japonica is used to induce vaginal dilation before surgical entry into the uterus through the vagina
• Phylum Rhodophyta (red algae)

  • Members have delicately branched thalli
  • Can live at greater ocean depths than other algae
  • A few have thalli that forms crustlike coatings on rocks and shells
  • The red pigments enable red algae to absorb the blue light that penetrates deepest into the ocean
• Applications of red algae

  • The agar used in microbiological media is extracted from many red algae
  • Carrageenan comes from a species of red algae commonly called Irish moss
  • Both carrageenan and agar can be used as a thickening ingredient in evaporated milk, ice cream, and pharmaceutical agents
  • Species of genus Gracillaria are used by humans for foods but some members of this genus can produce a lethal toxin
• Featured members of Phylum Rhodophyta

  • Microcladia sp.
  • Gracillaria parvispora
• Phylum Chlorophyta (green algae)

  • Members have cellulosic cell walls, contain chlorophyll a and b, and store starch
  • Believed to have given rise to terrestrial plants
  • Most are microscopic, although they may be either unicellular or multicellular
  • Some filamentous kinds form grass-green scum in ponds
• Featured members of Phylum Chlorophyta

  • Ulva sp., a multicellular green alga
  • Spyrogyra sp., a microscopic filamentous green alga
  • Chlamydomonas sp., a unicellular and motile green alga
• Kingdom Stramenopila: Diatoms


  • Unicellular or filamentous algae with complex cell walls that consist of pectin and a layer of silica
  • Symmetrical: the two parts of the wall fit together like the halves of a Petri dish
  • The distinctive patterns of the walls are a useful tool in diatom identification
  • Diatoms store energy captured through photosynthesis in the form of oil

  
• Some diatoms produce toxins such as domoic acid, which is concentrated in the mussels causing the first reported outbreak of neurological disease caused by diatoms in 1987 in Canada
• Domoic Acid Toxicosis


  Symptoms occurred within 24 hours of eating and included diarrhea and memory loss, with a fatality rate of less than 4%
• Diatoms


  • Eunotia serra, a freshwater diatom that grows in acidic water
  • Asexual reproduction of a diatom
• Kingdom Stramenopila: Dinoflagellates


  • Collectively called as phytoplanktons, these unicellular algae are free-floating
  • Their rigid structure is due to cellulose embedded in the plasma membrane
  • In the last two decades, a worldwide increase in toxic marine algae has killed millions of fish, hundreds of marine mammals, and even some humans
• Dinoflagellate Intoxications


  • Karenia brevis releases a neurotoxin that stops the fish from breathing upon their attachment to its gills
  • Alexandrium spp. releases saxitoxins causing paralytic shellfish poisoning (PSP) in humans upon consumption of infected mollusks harvested during red tide
  • Gambierdiscus toxicus causes the endemic ciguatera in humans who consume infected large fish in the south Pacific Ocean and the Caribbean Sea
  • Pfiesteria spp. is responsible for periodic massive fish deaths along the Atlantic coast
• Dinoflagellates


  • Peridinium sp.
  • A red tide
• Kingdom Stramenopila: Oomycota (water molds or oomycetes)


  • Decomposers that form cottony masses on dead algae and animals, usually in freshwater
  • Asexually resembles zygomycete fungi as they produce spores in a sporangium (spore sac) coined as zoospores
  • Have two flagella and are previously classified with the fungi
  • Cellulosic cell walls
  • Recent DNA analyses confirmed their close relations to diatoms and dinoflagellates
  • Many terrestrial water molds are plant parasites