Microbiology lesson 1-6

Characterize each of the following aspects of the protozoa. Habitats

They inhabit a wide bariety of habitats, both aquatic and terrestrial. Many are free living, while others are parasitic, carrying out a life cycle within a host or host and potentially causing illness.

Describe the unique property and/ or significance of each of the following: Giardia lamblia

This group includes Giardia lamblia (also known as G. intestinalis or G. duodenalis), a widespread pathogen that causes diarrheal illness and can be spread through cysts from feces that contaminate water supplies (Figure 5.3). Parabasalia are frequent animal endosymbionts; they live in the guts of animals like termites and cockroaches. They have basal bodies and modified mitochondria (kinetoplastids). They also have a large, complex cell structure with an undulating membrane and often have many flagella. The trichomonads (a subgroup of the Parabasalia) include pathogens such as Trichomonas vaginalis, which causes the human sexually transmitted disease trichomoniasis. Trichomoniasis often does not cause symptoms in men, but men are able to transmit the infection. In women, it causes vaginal discomfort and discharge and may cause complications in pregnancy if left untreated.

Stages in life cycles: trophozoite and cyst

Trophozoite is when they are in the feeding and growth part of their life cycle. These feed on small particulate food sources such as bacteria. Some types of protozoa exist exclusively in the trophozoite form, others can develop from trophozoite to an encapsulated cyst stafe when environmental conditions are too harsh for the trophozoite. Cyst is a cell with a protective wall, and the process by which a trophozoite becomes a cyst is called encystment. When conditions become more favorable, these cysts are triggered by environmental cues to become active again through excystment.

Excavata List the distinguishing characteristic(s) of this supergroup. The third and final supergroup to be considered in this section is the Excavata,

which includes primitive eukaryotes and many parasites with limited metabolic abilities. These organisms have complex cell shapes and structures, often including a depression on the surface of the cell called an excavate. The group Excavata includes the subgroups Fornicata, Parabasalia, and Euglenozoa. The Fornicata lack mitochondria but have flagella.

Identify the three major informal groups into which the Protists are divided.

"animal like" protozoans, the "plant-like" algae, and the "fungus-like" protists such as water molds.

Cell structure: plasmalemma, pellicle, ectoplasm, endoplasm, and cytostome

All protozoans have a plasma membrane, or plasmalemma, and some have bands of protein just inside the membrane that add rigidity, forming a structure called the pellicle. Some protists, including protozoans, have distinct layers of cytoplasm under the membrane. In these protists, the outer gel layer (with microfilaments of actin) is called the ectoplasm. Inside this layer is a sol (fluid) region of cytoplasm called the endoplasm. These structures contribute to complex cell shapes in some protozoans, whereas others (such as amoebas) have more flexible shapes (Figure 5.5). Different groups of protozoans have specialized feeding structures. They may have a specialized structure for taking in food through phagocytosis, called a cytostome, and a specialized structure for the exocytosis of wastes called a cytoproct. Oral grooves leading to cytostomes are lined with hair-like cilia to sweep in food particles. Protozoans are heterotrophic. Protozoans that are holozoic ingest whole food particles through phagocytosis. Forms that are saprozoic ingest small, soluble food molecules.

Describe the unique property and/or significance of each of the following: Entamoeba histolytica

Entamoeba includes commensal or parasitic species, including the medically important E. histolytica, which is transmitted by cysts in feces and is the primary cause of amoebic dysentery. Another member of this group that is pathogenic to humans is Acanthamoeba, which can cause keratitis (corneal inflammation) and blindness.

Types of motility: flagella, cilia, and pseudopodia

Many protists have whip-like flagella or hair-like cilia made of microtubules that can be used for locomotion (Figure 5.5). Other protists use cytoplasmic extensions known as pseudopodia ("false feet") to attach the cell to a surface; they then allow cytoplasm to flow into the extension, thus moving themselves forward.

The Protists List the general characteristics of the Protists.

Microscopic eukaryotic organisms, also look at the paper that your filled out.

Reproductive mechanisms

Some reproduce sexually and other reproduce asexually. Asexual reproduction occurs by binary fission, budding, or schizogony. Schizogony the nucleus of a cell divides multiple times before the cell divides into many smaller cells. The products of schizogony are called merozoites and they are stored in structures known as schizonts. Protozoans may also reproduce sexually, which increases genetic diversity and can lead to complex life cycles. Protozoans can produce haploid gametes that fuse through syngamy. However, they can also exchange genetic material by joining to exchange DNA in a process called conjugation. This is a different process than the conjugation that occurs in bacteria. The term protist conjugation refers to a true form of eukaryotic sexual reproduction between two cells of different mating types. It is found in ciliates, a group of protozoans, and is described later in this subsection.

Trypanosoma

The Euglenozoa also include the trypanosomes, which are parasitic pathogens. The genus Trypanosoma includes T. brucei, which causes African trypanosomiasis (African sleeping sickness and T. cruzi, which causes American trypanosomiasis (Chagas disease). These tropical diseases are spread by insect bites. In African sleeping sickness, T. brucei colonizes the blood and the brain after being transmitted via the bite of a tsetse fly (Glossina spp.) (Figure 5.18). The early symptoms include confusion, difficulty sleeping, and lack of coordination. Left untreated, it is fatal.

Euglena

The Euglenozoa are common in the environment and include photosynthetic and nonphotosynthetic species. Members of the genus Euglena are typically not pathogenic. Their cells have two flagella, a pellicle, a stigma (eyespot) to sense light, and chloroplasts for photosynthesis (Figure 5.17). The pellicle of Euglena is made of a series of protein bands surrounding the cell; it supports the cell membrane and gives the cell shape.

Cellular slime molds and acellular slime molds

The Eumycetozoa are an unusual group of organisms called slime molds, which have previously been classified as animals, fungi, and plants (Figure 5.9). Slime molds can be divided into two types: cellular slime molds and plasmodial slime molds. The cellular slime molds exist as individual amoeboid cells that periodically aggregate into a mobile slug. The aggregate then forms a fruiting body that produces haploid spores. Plasmodial slime molds exist as large, multinucleate amoeboid cells that form reproductive stalks to produce spores that divide into gametes. One cellular slime mold, Dictyostelium discoideum, has been an important study organism for understanding cell differentiation, because it has both single-celled and multicelled life stages, with the cells showing some degree of differentiation in the multicelled form. Figure 5.10 and Figure 5.11 illustrate the life cycles of cellular and plasmodial slime molds, respectively.

Describe the unique property and/or significance of each of the following: Apicomplexans

The apicomplexans are intra- or extracellular parasites that have an apical complex at one end of the cell. The apical complex is a concentration of organelles, vacuoles, and microtubules that allows the parasite to enter host cells (Figure 5.12). Apicomplexans have complex life cycles that include an infective sporozoite that undergoes schizogony to make many merozoites (see the example in Figure 5.4). Many are capable of infecting a variety of animal cells, from insects to livestock to humans, and their life cycles often depend on transmission between multiple hosts. The genus Plasmodium is an example of this group.

Dinoflagellates (see page 232)

The dinoflagellates and stramenopiles fall within the Chromalveolata. The dinoflagellates are mostly marine organisms and are an important component of plankton. They have a variety of nutritional types and may be phototrophic, heterotrophic, or mixotrophic. Those that are photosynthetic use chlorophyll a, chlorophyll c2, and other photosynthetic pigments (Figure 5.35). They generally have two flagella, causing them to whirl (in fact, the name dinoflagellate comes from the Greek word for "whirl": dini). Some have cellulose plates forming a hard outer covering, or theca, as armor. Additionally, some dinoflagellates produce neurotoxins that can cause paralysis in humans or fish. Exposure can occur through contact with water containing the dinoflagellate toxins or by feeding on organisms that have eaten dinoflagellates. When a population of dinoflagellates becomes particularly dense, a red tide (a type of harmful algal bloom) can occur. Red tides cause harm to marine life and to humans who consume contaminated marine life. Major toxin producers include Gonyaulax and Alexandrium, both of which cause paralytic shellfish poisoning. Another species, Pfiesteria piscicida, is known as a fish killer because, at certain parts of its life cycle, it can produce toxins harmful to fish and it appears to be responsible for a suite of symptoms, including memory loss and confusion, in humans exposed to water containing the species.

Naegleria fowleri

The notorious "brain eating amoeba," Naegleria fowleri, is a considered a distant relative of the Amoebozoa and is classified in the phylum Percolozoa.

Diatoms (see page 232-233)

The stramenopiles include the golden algae (Chrysophyta), the brown algae (Phaeophyta), and the diatoms (Bacillariophyta). Stramenopiles have chlorophyll a, chlorophyll c1/c2, and fucoxanthin as photosynthetic pigments. Their storage carbohydrate is chrysolaminarin. While some lack cell walls, others have scales. Diatoms have frustules, which are outer cell walls of crystallized silica; their fossilized remains are used to produce diatomaceous earth, which has a range of uses such as filtration and insulation. Additionally, diatoms can reproduce sexually and asexually, and the male gametes of centric diatoms have flagella providing directed movement to seek female gametes for sexual reproduction.

Taxonomy of Protists Amoebozoa List the distinguishing characteristic(s) of this supergroup.

The supergroup Amoebozoa includes protozoans that use amoeboid movement. Actin microfilaments produce pseudopodia, into which the remainder of the protoplasm flows, thereby moving the organism

Chromalveolata List the distinguishing characteristic(s) of this supergroup.

The supergroup Chromalveolata is united by similar origins of its members' plastids and includes the apicomplexans, ciliates, diatoms, and dinoflagellates, among other groups (we will cover the diatoms and dinoflagellates in Algae). The apicomplexans are intra- or extracellular parasites that have an apical complex at one end of the cell. The apical complex is a concentration of organelles, vacuoles, and microtubules that allows the parasite to enter host cells