Oomycetes

Oomycetes CN. 07, 15, 12, 13, 05, 21

Introduction What are oomycetes? Oomycetes, a.k.a water molds, are fungus-like protists, that feed on decaying organic material by absorbing nutrients through their cell walls, which are made of cellulose. “Oomycetes” came from the Greek words “oion”, which means “egg”, and “mukes”, meaning “fungus”. Therefore, “oomycetes” means “egg fungi”.

Characteristics Anatomy and Functions Their cell walls are composed of cellulose. Its main purpose is to absorb food from its surroundings. Most oomycetes produce self-moving spores, which are called as zoospores. These spores swim through water in search for food. They also have two(2) flagella. These flagella have different structures and functions.

Characteristics Anatomy and Functions Oomycetes have tubular mitochondrial cristae(Cristae are the internal “rooms” formed by the inner membrane of a mitochondrion). Filamentous, coenocytic, sometimes unicellular.

Characteristics Habitat Although they (oomycetes) are commonly known for their other name, “water molds”, not all of them live near bodies of water. Most of them are terrestrial.

Characteristics Reproduction Diploid life cycle. Sexual Reproduction Oogonium (Female Gametophytes) Antheridium (Male Gametophytes) Spores: biflagellate zoospores Asexual Reproduction Spores: oospores

Life Cycle sporangium (2n) hypha oosphere (2n) mycelium (2n) zoospores Antheridium; produces fertilization tubes (n) Oogonium; containing oospores (n)

Life Cycle Life Cycle of Saprolegnia Sp.

Water Molds vs. Fungi Water molds have cellulose for their cell walls, while fungi have chitin. Water molds have diploid nuclei, whereas fungi have haploid nuclei. Self-motile spores of oomycetes usually have two(2) flagella, while fungal spores have only one(1). They both have different metabolic pathways for synthesizing lysine(an essential amino acid). Number of certain enzymes differ.

Impacts On Animals Some water molds are parasites to some animals. They can grow on scales/eggs of some fishes/amphibians. One good example is the water mold Saprolegnia. They are parasitic to organisms such as rotifers, nematodes, arthropods, and diatoms.

Impacts On Plants Some water molds affect plants, too, such as root-rotting fungi, seedling-dampening mold, blister rusts, white rusts (Albugo), and downy mildews. They invade plants like grapes, lettuces, corns, cabbages, and many other crop plants. Two water molds have had a major impact on world history: Phytophthorainfestans, which causes Late Blight of Potato, and; Plasmoparaviticola, which are the downy mildews of grapes.

Impacts On Humans The two water molds mentioned earlier, Phytophthorainfestansand Plasmoparaviticola, affected many crops (potatoes, grapes, etc.), it also affected people and some of their jobs in those early times. The Great Potato Famine, is one of the greatest problems that these water molds gave us.

Gallery Reproductive Structures of Phytophthorainfestans

Gallery Sporangium of Phytophthorainfestans

Gallery A water mold from a stream

Links http://encarta.msn.com/dictionary_561534904/oomycete.html; http://www.ucmp.berkeley.edu/chromista/oomycota.html; http://en.wikipedia.org/wiki/File:Phytophtora_reproduction.png; http://en.wikipedia.org/wiki/Oomycetes; http://www.aber.ac.uk/fungi/fungi/taxonomy.htm; http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb2pg2.htm

Oomycetes

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