Protists: Eukaryotic Microbes

Protists Overview

• Protists are eukaryotic microbes that are the first to have a true nucleus.
• They exhibit vast ecological diversity with between 65,000 to 200,000 species.
• Examples of protists are amoebas, paramecium, and diatoms.
• Protists include any organism that doesn't fit into other kingdoms.
• Some protists are large enough to be seen without magnification.
• The majority are unicellular, but some are simple multicellular organisms.
• Protists reproduce asexually through binary fission, multiple fission, or mitosis, while some reproduce sexually through meiosis.
• Protists inhabit mostly aquatic enviroments, damp areas like moist soil, or within other organisms.
• Fungi, plants, and animals, are also protists.
• Protists are divided into three general groups: plant-like, fungi-like, and animal-like

Unicellular Protists

• Animal-like protists, or protozoans, include amoebas, ciliates, and flagellates, which consume other organisms and some are parasites
• Plant-like protists include euglenoids, diatoms, and dinoflagellates that produce food through photosynthesis, consume organisms when light is scarce, and some are symbionts.
• Fungus-like protists include slime molds and water molds that absorb nutrients from living or dead organisms consume other organisms, and some are parasites.

Animal-like Protists

• Often called protozoa.
• They are heterotrophs and unicellular.
• They have contractile vacuoles to eliminate excess water.
• Protists exist in aquatic habitats as predators, decomposers, or in symbiotic relationships. These relationships include parasitism, mutualism, and commensalism.
• Animal-like protists are classified by their motility.

Cercozoans (Amoebas)

• Found in moist soil, water (including human-made pipelines), and within other organisms.
• Amoebas are heterotrophic.
• They have pseudopods, also known as "fake feet".
• Pseudopods are extensions of the cytoplasm that are used to ingest food.
• Its main parts are cytoplasm, plasma membrane, and a nucleus.
• Amoebas lack Cilia and flagella.

Brain-Eating Amoeba

• A species of amoeba called Naegleria fowleri.
• Found in warm lakes/ponds, untreated swimming pools, hot springs, aquariums, and moist soil.
• Food source is bacteria, but it can feed on brain tissue, when infecting humans.
• Usually infected through the nose during water sports like diving or water skiing.
• Symptoms of infection: headache, fever, stiff neck, loss of appetite, vomiting, seizures, coma, and eventually, death.

Ciliates (Paramecium)

• Found in bodies of water mostly stagnant and within other organisms.
• Paramecium is heterotrophic.
• They use cilia for locomotion and to manipulate particles.
• They are oral grooves and gullet-like structures. Cilia move nutrients into the gullet.
• They have two nuclei and consist of macro and micro nuclei.
• The macronucleus provides the nuclear RNA for vegetative growth
• Mating cells exchange haploid micronuclei and a new macronucleus develops from a new diploid micronucleus that are involved in sexual reproduction.

Flagellates (Trichonympha)

• Found in aquatic environments, including snow, and within multicellular organisms as part of a mutualistic or parasitic relationship.
• Flagellates are heterotrophic.
• They use one or more flagella for motility.
• These protist have an elongated shape and flagella.

Sporozoans (Plasmodium)

• Mostly Parasitic
• These protist are heterotrophic
• Reproduce by binary fission, and most alternate between sexual and asexual reproduction
• Most of these protists move without flagella, cilia, or pseudopods
• They have a parasitic lifecycle that often occurs within 2 different host species, and have a spore-like stage.
• Malaria is caused by plasmodium.
• The female Anopheles mosquito bites and injects sporozoites into a human host. These sporozoites travel through the blood to the liver. Hepatocytes become infected by sporozoites that mature to schizonts that rupture and release merozoites. Released merozoites go on to infect erythrocytes and mature into gametocytes which are released. A mosquito ingests gametocytes where they undergo stages of their life cycle, and can then repeat the cycle by injecting sporozoites into a new host.

Plant-like Protists

• Commonly called algae.
• Chloroplasts enable photosynthesis, making them mostly autotrophic, though some are mixotrophic.
• Accessory pigments give them variety of colours.
• Capable of asexual and sexual reproduction.
• Live in wet or moist environments.

Diatoms

• Diatoms produce a lot of oxygen through photosynthesis, accounting from around 20–50% of the oxygen generated by photosynthesis.
• Cell walls are made of silica.
• The shells of dead diatoms make up a significant portion of the ocean floor, up to 800 meters deep.
• Important food source of aquatic organisms.
• They are mostly found in the open water, unicellular
• Most abundant type of phytoplankton living in aquatic environments
• They go through Mitosis (asexual) and Meiosis (sexual) for reproduction. These organisms float around in the water
• Cell wall coated in silica in shoebox style
• Diatoms get their name from having shape like a shoe box, with the “lid” fitting complementary to, and over the base.
• They mostly reproduce through asexual mitosis, but during unfavourable conditions they reproduce via meiosis.

Dinoflagellates

• Phytoplankton living in aquatic environments.
• They are autotrophic.
• The flagella cause them to spin through the water.
• They have two flagellum positioned 90° (perpendicular) to one another.
• Pigments give distinctive colours.
• Rapid reproduction during optimal conditions leads to algae blooms, which can cause death or increased toxicity to marine life.
• Mutualism when dinoflagellates live within coral, and in warmer temperatures, the coral expels the dinoflagellates.

Euglenoids (Euglena)

• Found in shallow water.
• Autotrophic, but can switch to heterotrophic when needed.
• Uses flagellum for mobility.
• Stigma allows them to move toward or away from light.

Algae

• Most algae are aquatic, while others are terrestrial in moist soil, trees, and rocks.
• Algae can be Unicellular and others are multicellular, it does not have tissues except for some brown algae
• All algae are autotrophic
• They reproduce using Mitosis (asexual) Meiosis (sexual)
• Algae will float, or will attach to objects within the water or on land
• Algae differs from the vascular plants by lacking true roots, stems, and leaves
• Algae includes: phylum Chlorophyta (green algae), phylum Phaeophyta (brown algae), phylum Rhodophyta (red algae), and phylum Chrysophyta (golden algae).

Fungus-like Protists

• These protists resemble fungi in appearance and lifestyle with some key differences at their cellular level, specificially the cell wall
• Fungus like protist reproduces with spores like fungus
• Fungus like protist Heterotroph feed on bacteria and rotting material
• Some of the fungis like protists includes water mould and slime mould

Plasmodial Slime Molds

• Start out as individual amoeboid cells, but join to form a multi-nucleate mass having only one cellular membrane which is called a plasmodium.
• Plasmodium moves over dead, decaying material looking for bacteria and sometimes fungi to engulf and digest.
• When plasmodium runs out of food or dries out, it forms fruiting structures called sporangia.
• Sporangia produces diploid nuclei which undergoes meiosis and produces haploid nuclei which makes/dispersal spores for aerial dispersal that makes it look like a fungus
• When the spores land, they germinate into haploid cells with two flagella.

Cellular Slime Molds

• Cellular Slime Molds are rarely visible to the naked eye
• There is One nuclei in each cellular slime mold
• At times, individuals may join to form a pseudoplasmodium