Protozoa Reproduction and Characteristics

• Protozoa no longer has a taxonomic status.

Current Use of Protozoa

• Encompasses animal-like members of the Kingdom Protista or Protoctista.
• Defines a polyphyletic assemblage of primarily single-celled, heterotrophic, eukaryotic organisms.
• Protozoa are individual cells, a characteristic that sets them apart from animals.
• A single eukaryotic cell in protozoa performs all physiological processes or life functions.
• These include feeding and digestion, locomotion, excretion and osmoregulation, sensory and response behaviors, and reproduction.
• Protozoa use specialized organelles to carry out life functions.
• Protozoa are sometimes called acellular organisms, in contrast to multicellular organisms.

General Characteristics: Structural Support and Protection

• Structural support and protection are provided by:
• A cell membrane or plasmalemma, which is present alone in naked/flexible Amoebas.
• A thickened plasmalemma with protein filaments and microtubules & vesicles (alveoli), forming a pellicle, an example is Paramecium.
• A secreted shell-like covering or material, like sand particles, forms a test or lorica (skeleton).

Cytoplasm Differentiation

• Ectoplasm is the gelatinous outer layer.
• Endoplasm is the fluid inner layer.

Locomotion and Feeding Structures

• Structures used for locomotion and feeding are:
• Flagella.
• Cilia.
• Pseudopodia, which are flowing extensions of cell cytoplasm.
• The "9+2" tube of fibrils called an axoneme is seen in both Cilia & Flagella & are considered homologous structures.
• These structures are used to characterize many protozoa taxa.

Nutrition Types

• Autotrophic organisms rely on photosynthesis but not always.
• Heterotrophic organisms have different modes of feeding
• Saprobic organisms take in dissolved organic matter through diffusion, active transport or pinocytosis.
• Holozoic organisms take in solid foods (organic detritus or prey) by phagocytosis.
• Symbiotic organisms are
• Parasites like Plasmodium and Trypanosoma.
• Mutualists like Trychonympha in wood-eating insects.
• Commensals like Ciliates in rumen of ungulates.
• Digestion occurs in membrane-bounded food vacuoles.
• Food vacuoles may form on fixed sites = cell mouth = cytostome, for example Paramecium.
• Food vacuole may form on any site on cell surface, for example Amoeba.
• Undigested materials are discharged.
• Cytoproct which are permanent pores in ciliates.
• Anywhere on cell surface, for example Amoeba.

Gas Exchange

• Simple diffusion is used for O2 uptake and CO2 release.

Excretion & Osmoregulation

• Excretion and Osmoregulation:
• Are usually intimately associated.
• Excretion involves the elimination of metabolic waste products, especially excess nitrogen produced as NH3 from deamination of amino acids.
• NH3 is highly soluble but quite toxic.
• Excretion is achieved by simple diffusion.
• Osmoregulation is the regulation of of water and ionic balance. -Balancing hypertonic vs hypotonic environments poses a challenge for freshwater protozoans.
• They achieve this through active transport and contractile vacuoles that work with tubules, water tracts, and small vesicles.

Sensitivity & Response

• Protozoa show sensitivity due to:
• Conductivity of protoplasm.
• Cilia and flagella being touch-sensitive.
• Extrusomes, which are membrane-bound organelles capable of ejecting material.
• Eye spots or stigmata, that are photo-sensitive.

Reproduction

• Asexual reproduction:
• Binary fission where one cell splits into 2 similar daughter cells.
• Multiple fission where the nucleus divides repeatedly before cytokinesis, resulting in more than two progeny.
• Budding where a portion of the parent breaks off and differentiates into a new individual.
• Plasmotomy that occurs in some multinucleate species.

Common Life Stages

• Many protozoans have cyst stages which are secreted by trophic or spore stages,
• Cysts and spores have four basic functions:
• Protection against unfavorable conditions.
• Serving as sites for multiplication.
• Assisting in attachment to surfaces such as hosts.
• Aiding in transmission stage from host to host.

Sexual Reproduction

• Syngamy produces n cells that fuse to restore 2n condition,
• Isogamy where gametes are similar in size and shape.
• Anisogamy where gametes are of two distinct types.
• Autogamy where re-formation of a genetically new nucleus within a single individual.
• Conjugation where genetic mixing occurs by the exchange of nuclear material between mates.

Higher Classification & Biology

• Phylum Sarcomastigophora includes amoebas and flagellates. -Organisms that use flagella or pseudopodia or both. -Organisms that are autotrophic or heterotrophic.
• Subphylum Mastigophora includes flagellates, with the unifying feature possession of ≥1 flagella.
• It is considered polyphyletic.
• Class Phytomastigophorea includes photosynthetic flagellates.
• Class Zoomastigophorea that includes non-photosynthetic flagellates.

Phytomastigophorea specifics

• Order Euglenida:
• Commonly found in ponds rich in decaying organic matter.
• Body shape maintained by pellicle.
• Most have 2 flagella of unequal lengths
• About 1/3 of photosynthetic species store food reserves as starchy paramylon.
• About 2/3 of euglenids are heterotrophic.
• Reproduction appears to be exclusively asexual.
• Euglena and Peranema are examples.

Order Dinoflagellida

• Biflagellate, free-living or symbiotic in freshwater marine habitats.
• The body shape is maintained by pellicle which contains alveolar vesicles.
• The alveoli may be filled with cellulose.
• 50% of species are photosynthetic while the rest are heterotrophic or both.

Order Volvocida

• Volvox and Chlamydomonas

Zoomastigophora specifics

• Order Choanoflagellida:
• Uniflagellate, sessile protozoans that are either solitary or colonial.
• All free-living.
• A flagellum encircled by a protoplasmic collar, which is similar to sponge choanocytes.
• It is viewed as a transitional link to sponges or as Metazoan ancestors.
• This is supported by DNA.

Order Kinetoplastida

• Trypanosomes & relatives, with a body shape maintained by non-alveolate pellicle.
• They are uni- or bi-flagellate, and reproduce asexually through binary fission
• Trypanosomes:
• Exclusively parasitic in plants, invertebrates and vertebrates.
• Have a cell with a glycoprotein layer which protects against the host immune system, with glycoprotein composition that changes regularly. Glycoprotein composition changes regularly (coded for by ~1000 different genes).
• Vertebrate parasites that cause several serious diseases:
• Leishmaniasis, like Leishmania sp. that effects humans, phlebotomine sandflies, causes Kala-azar and skin sores and ulcers.
• Trypanosomiasis such as Trypanosoma spp. and includes Nagana (T. brucei) affecting Ungulates where the vector is a Tsetse-fly.
• sleeping sickness (T. gambiense and T. rhodesiense) affecting Humans where the vector is Tsetse-flies, and Chagas' disease (T. cruzi) affecting Humans and the vector are Kissing bugs.

Parasitic Mastigophora & Diseases

• Tissue parasites:
  • Leishmania, causes Leishmaniasis, Kala-azar/black fever which can attack the skin, liver, spleen, causing visceral, cutaneous and mucocuteneous leishmaniasis.
• Intestinal parasites such as Giardia lamblia, found in contaminated water bodies.
• Symptoms manifest within 3 to 25 days. -Symptoms include abdominal cramps, stomach bloating, and intermittent episodes of diarrhea and tiredness and are diagnosed through laboratory examination of a faecal specimen.
• Reproductive organs such as Trichomonas vaginalis four flagellates, forms a trophozoites.

Order Diplomonadida

• Symbiotic flagellates that are both commensals and parasites in vertebrate digestive tracts and have paired nuclei with each nucleus associated with a bundle of flagella. They also lack mitochondria.
• The mode of reproduction is asexual.
• An example is Giardia lamblia, a cosmopolitan symbiont in human digestive tract, causes giardiasis (diarrhea, dehydration & intestinal pain).

Order Trichomonadida

• Have ≥4 flagella, lack mitochondria, and are commensal or parasitic symbionts.
• Trichomonas vaginalis is sexually transmitted.
• Most strains have low pathenogenicity asymptomatic or other strains cause severe inflamation (itching & discharge)\
• T. tenax = oral commensal/parasite.
• Obligate mutualists, such as Trichonympha in digestive tracts of wood-eating termites & roaches.

Subphylum Sarcodina specifics

• The Amoebas have primary locomotion through pseudopodia, which take several forms.
• Lobopodia are typically broad with rounded tips (like fingers).
• Filopodia are threadlike and often branch.
• Reticulopodia always branch extensively and anastomose, forming dense pseudopodial networks.
• Axopodia have pseudopodia stiffened by an inner core of microtubules. Microtubules run along the length through its center.

Superclass Rhizopoda

• Superclass Rhizopoda:
• Organisms That use lobopodia or filopodia and are common in moist or aquatic habitats, where most are free-living; some endosymbiotic.
• The life cycle in many involves cysts and trophozoites. Class Lobosea is made up of sarcodines with lobose to filiform pseudopodia. -The Class Lobosea includes the Order Amoebida, which has naked Lobosea such Amoeba and Entamoeba, or a free-living Amoeba and Entamoeba coli a cosmopolitan commensal in human intestines, Entamoeba gingivalis a commensal in teeth & gums. Also Entamoeba histolytica, a serious parasite in humans, causes amoebic dysentery.
• The Class Lobosea also contains the Order Arcellida, which contain shelled or testate Lobosea,
• This includes Arcella secreted shell, Difflugia, a shell that is constructed from sand grains with some also using the free-living in freshwater class.
• Class Filosea includes rhizopodans with filiform pseudopodia with simple or branching filopodia, and are common in moist or aquatic habitats, where most are free-living; some endosymbiotic.

Phylum CILIOPHORA

• The ciliates maintain a higher classification that remains unchanged.
• They typically possess cilia categorized by function and structure.
• Functional cilia categories:
• Oral ciliature is associated with cytostome and surrounding area, aiding in feeding.
• Somatic ciliature is on the general body surface, used for for locomotion.
• Structural cilia categories:
• Simple cilia is categorized as one structural category
• Compound ciliature has a few types
• Cirrus is a discrete bundle of cilia in a row that tapers toward its tip..
• Membranelle is a Membranelle, cilia in several adjacent rows leaning toward each other.
• an undulating membrane is a flattened sheet of cilia that move as a unit.
• The cytostome position on the cell body varies and has taxonomic significance, and can be anteriorly, laterally or ventrally located.
• The pellicle consists of alveoli
• It’s considered homologous with that of Dinoflagellates and Apicomplexa
• a water expulsion vesicle fixed in position.

Dimorphic Nuclei

• Dimorphic nuclei or heterokaryotic:
• The macronucleus is polyploid and vegetative.
• The micronucleus is diploid and reproductive.

Lifestyle

• About 2/3 are free-living.
• Most are mobile and holozoic like Paramecium; some form temporary attachments.
• Others are permanently sessile (attach to substratum)
• 1/3 are symbiotic in or on invertebrates and vertebrates.
• Some are parasitic like Balantidium coli

Reproduction in Ciliates

• Sexual reproduction by conjugation results in two compatible mating conjugants that adhere to each other at their oral grooves.
• The pellicle then breaks down, and a cytoplasmic bridge is formed. Respective macronuclei disintegrate.
• Each micronucleus divides meiotically, resulting in 4 daughter micronuclei. Three of these newly formed micronuclei disintegrate and disappear.
• The lone surviving micronucleus divides once mitotically to form two identical gametic nuclei.
• Exchange of the male gametes then takes place across the cytoplasmic bridge to an opposing conjugant. Male and female fuse forming the zygotic nucleus.
• Conjugants separate and go independently.
• The zygotic nucleus divides mitotically forming eight daughter nuclei.
• Four transform into macronuclei and other four into micronuclei. Three daughter micronuclei degenerate, leaving only one.
• The ex-conjugants undergo binary fission.
• Two macronuclei enter each new cell, and micronucleus divides mitotically.
• Further division takes place where the two macronuclei separate with one going into a separate cell and the respective micronucleus dividing.
• As a result, there are now eight daughter cells from two separated ex-conjugants with four cells from each original ex-conjugant.

Sexual Reproduction

• Syngamy = production of n cells that fuse to restore 2n condition
• Isogamy = gametes are similar in size and shape.
• Anisogamy = gametes of two distinct types.
• Autogamy = re-formation of a genetically new nucleus inside a single individual.
• Conjugation = genetic mixing by the exchange of nuclear material between mates.

Phylum Apicomplexa

• Higher Classification splits it in two classes
• Class Gregarinea
• Class Coccidia

Gregarinea

• Parasites of invertebrates, mainly annelids and arthropods, that infect the body cavity, intestine or reproductive system of hosts.
• Most species produce a resistant spore or oocyst (sporocyst with sporozoites) and hosts are typically infected by ingesting spores.
• The life cycle usually involves one host in the following 2 phases : sporogony and gamogony.
• Examples are Monocystis lumbrici, Gregarina cuneata,and Stylocephalus longicollis.

Coccidia

• Coccidia are primarily parasites of vertebrates, in epithelium of digestive tract, liver, kidneys or blood cells.
• The parasites are intracellular
• The life cycle has 3 major phases: merogony, gamogony & sporogony . An example is Plasmodium spp which has life cycles invloving 2 hosts
• Characterized by the presence of apical complex, which is important for attaching the parasite and or facilitating entry into a host cell.
• Found at anterior end, beneath cell membrane of motile infective stages
• Sporozoites and merozoites stages, are present in cell
• Strengthened cell membrane formed in to alveolar pellicle. With a single Nucleus located interior.

Apicomplexans

• Parasites of Animals, and some are the leading causes of serious human diseases
• Have One edge, that contains the apical complex, contains that is specializeed for penetrating a host
• Hosts must have both Sexual and asexual stages that require two or more additional host species for completion. The apicomplexan Plasmodium is the parasite that causes Malaria.
• Plasmodium involves both hosts.
• Requires Both mosquitoes and humans to complete its life cycle
• Close to two-million are killed as a result each year from malaria and or are children( Mainly those under five years).

Malaria

• Characterized by an intermittent fever occurring every 48 or 72 hours, that depend on the specific species.

Prevention of malaria

• Avoid the parasite
• Ensure a Female anopheles mosquito is not present Long sleeved clothes -Use of Repellants such as Sprays -Have protection suchas, Screens on doors and windows in housing areas Isolate, Being indoors during after dusk

Other techniques:

• Use Biological techniques to remove sterlie males so the parasite cannot reproduce

Environmental

• Remove vegetation near settlements to remove areas used for the parasite Remove stagnant water
• Medication from Treatment/prophylaxis, such as Malaria Tablets or injections when going to malaria areas. -(Atovaquone/Proguanil also known as ,Malarone), Chloroquine, Doxycycline, Mefloquine, Primaquine, Tafenoquine

Explore protozoa reproduction, including conjugation and nuclear division. Learn about apicomplexans, entamoeba species, and gregarines. Understand ciliate characteristics and mastigophora subphylum features.