Eukaryotes PDF

Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé MICROBIOLOGY - PROFFESOR GARLAND 15.10.2021 – CHARACTERIZING AND CLASSIFYING EUKARYOTE This lecture is an overview about eukaryotes, particularly on those involved with human disease. It will mainly focus on fungi. Eukaryotes are divided into mi...

Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé MICROBIOLOGY - PROFFESOR GARLAND 15.10.2021 – CHARACTERIZING AND CLASSIFYING EUKARYOTE This lecture is an overview about eukaryotes, particularly on those involved with human disease. It will mainly focus on fungi. Eukaryotes are divided into micro organisms and organisms: the micro organisms are protozoa, fungi, algae, water moulds, slime molds; whereas the organisms are parasitic helminths and arthropods. Eukaryotes include human pathogens such as malaria, amebiasis, toxoplasmosis… and organisms vital for human life: e.g. they produce oxygen, provide the basis of oceans’ food chains, fungi produce antibiotics; yeasts are useful for bread and alcoholic beverages production. Eukaryotes have a more complicated reproductive mechanism compared to eukaryotes: the DNA is packed as chromosomes in the nucleus, many reproduce sexually forming gametes and zygotes but others reproduce asexually with binary ssion, budding, fragmentation, spore formation, schizogony. Algae, fungi and some protozoa can reproduce both sexually and asexually. Eukaryotic nucleus has one or two complete copies of genome: haploid eukaryotes include most fungi, many algae, some protozoa; the diploid ones include fungi, algae, protozoa, plants, animals. Gametes are always haploid, zygotes are diploid. The reproductive drive is carried out through mitosis (for somatic cells) or through meiosis (sexual reproduction). MITOSIS Mitosis is a process in which the cell partitions replicated DNA equally between two cells; an important feature is that mitosis maintains ploidy of parent nucleus . Mitosis is taking place in four phases: 1. Prophase: DNA molecules are condensed in 2 chromatids joined at centromere, nuclear envelope disintegrates , 2. Metaphase: chromosomes line up on a plane in the middle of the cell and attach to spindle, 3. Anaphase: chromatids separate, 4. Telophase: chromosomes are compact, formation of the nuclear envelope MEIOSIS Meiosis is a nuclear division that partitions chromatids into four nuclei In this process, diploid nuclei produce haploid daughter nuclei. Genetic recombination provides genetic variety in the next generation. It involves two stages – meiosis I and meiosis II - and each of them is composed of prophase, metaphase, anaphase, telophase. S fi fi A A key moment in the reproduction of eukaryotes is cytokinesis, so when the cytoplasms of the two daughter cells divide. A ring of actin micro laments contracts pinching the cell in two. Typically it occurs simultaneously with telophase of mitosis. In some algae and fungi, it is postponed or does not occur at all, resulting in multinucleated cells. Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé SCHIZOGONY Some protozoa (e.g. Plasmodium, the cause of malaria) reproduce asexually within red blood cells or liver cells via schizogony: multiple mitosis, generating multinucleate schizont. When cytokinesis occurs, numerous uninucleate merozoites are released, causing fever. EUKARYOTES CLASSIFICATION Eukaryotes are classed in di erent kingdoms based on their genetic relatedness: fungi, parabasala, diplomonadida, euglenozoa, alveolata, rhizaria, amoebozoa, stramenopila, rhodophyta, plantae, animalia. The pioneer of eukaryotic classi cation was Linnaeus in the late 18th century. ff fi fi fl fi fl ff ff PROTOZOA They have di erent characteristics one from the other, but they have something in common still: they are all eukaryotic, unicellular, and lack a cell wall. Protozoa is not a currently accepted taxon. They are motile by means of cilia, agella, pseudopods. The only ones which aren’t motile are the subgroup of apicomplexans. Protozoa require moist environments, and they live in ponds, streams, lakes, and oceans (where they compose the plankton). Others live in moist soil, beach sand, and decaying organic matter. Very few protozoa are pathogens. Morphologically, they are very diverse: some have two nuclei, a macronucleus (containing many copies of the genome) and a micronucleus (involved in genetic recombination, sexual reproduction). They have a variety in number and kinds of mitochondria. Some have contractile vacuoles that pump water out of the cells. They have di erent stages in their life cycle, a motile feeding stage called trophozoite and a resting one called a cyst. The motile feeding stage is called a trophozoite. In pathogenic species, this is the feeding and reproducing stage that lives within the host. Resting stage called a cyst involves a thick capsule and low metabolic rate. There is not a reproductive structure. This is the infective form that survives in the environment and undergoes excystment when ingested, developing into trophozoite. Trophozoites undergo encystment before leaving the host in faeces. Most protozoa are chemotropic: they obtain nutrients by phagocytizing bacteria, decaying organic matter, other protozoa, or the tissues of hosts. Few absorb nutrients from surrounding water, some (dino agellates and euglenoids) are photoautotrophic (capable of using light energy to synthesize organic compounds), so once classi ed as algal plants. Most protozoa reproduce asexually, through binary ssion or schizogony; few also have a sexual reproduction: some become gametocytes that fuse to form diploid zygotes, some utilize a process called conjugation. Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé CLASSIFICATION OF PROTOZOA Protozoa are classi ed into six kingdoms, and this classi cation has been updated and revised based on 18 rRNA sequences. The groups are: 1. Parabasala: parabasal body = Golgi body-like structure; lack mitochondria. One example is trichomonas: lives in human vagina, can cause severe in ammation and sterility. 2. Diplomonadida: Have two equal-sized nuclei and multiple agella. No mitochondria or Golgi bodies. One example is giardia: diarrhea-causing pathogen for animals and human. 3. Euglenozoa: Characteristics of both plants and animals. Kinetoplastids=a single large mitochondrion, kinetoplast. Trypanosoma and Leishmania: potentially fatal diseases transmitted by bloodsucking insects. 4. Alveolates (they have cavities or alveoli beneath the cell membrane. They are divided into two categories, ciliated and apicomplexans. Ciliates use cilia to move themselves or water; all are chemoheterotrophs and have two nuclei. One example is balantidium, causing diarrhoea. The other type of alveolates are apicomplexans: chemoheterotrophic pathogens of animals. A complex of organelles allow them to penetrate host cells. Life cycles involve at least two types of hosts. Schizogony is a major feature of apicomplexan life cycles: multinucleate schizonts form before cells divide. Some examples are the plasmodium (causing malaria), the cryptosporidium causing cryptosporidiosis and the toxoplasma (pathogen causing toxoplasmosis). Dino agellates, the third type of alveolates, posses photosynthetic pigments, historically they have been classi ed as algae, they are one of the major components of plankton. Many of them are bioluminescent, and they cause the ocean to light up upon movements (may cause red tides). Some dino agellates produce neurotoxins, and they are the major cause of poisoning due to shell sh eating. 5. Rhizaria are amoebae with threadlike pseudopods extending through a porous shells composed of calcium carbonate or silica. They often live attached to the ocean oor and most are fossil species and part of thick layers of limestone. Others are part of marine plankton. Non of them is pathologic. 6. Amoebozoa are amoebae with lobe-shaped pseudopods and no shells. They are protozoa with no truly de ned shape. They move and acquire food through the use of pseudopods. They are in water sources throughout the world. fl . fl fl fi fi fl fi . fi fi fi . I fl FUNG Fungi include molds, mushrooms and yeasts. They are chemoheterotrophic. They have cell walls typically composed of a nitrogenous polysaccharide called chitin and, since they lack clorophil, they do not perform photosynthesis. They are related to animals in terms of genetic sequence. Most fungi have a bene cial impact towards the environment and human beings, since they decompose dead organisms and recycle their nutrients, associate to plant roots helping plants absorb water and minerals, they are used for food and in manufacture of foods and beverages, they are used in antibiotics production and for immunosuppressive drugs production (e.g. cyclosporine and cholesterol reducing melvinic acid), they serve as important research tools Only 30% of the fungi are pathogenic, and they cause diseases called mycoses. Only 4 fungal species constitute a serious pathogenic source for humans, and the others are opportunistic fungi, meaning they only cause disease in particular conditions These fungi can spoil fruit, pickles, jams, jellies, since they tolerate high concentrations of salt, sugar and acidity. They are also able to survive in extreme conditions such as hypertonicity Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé MORPHOLOGY OF FUNG Fungi possess a vegetative body called thallus. In molds, the thallus is composed of long, branched, tubular laments called hyphae. Hyphe can be septed (cells are divided by cross walls called septa) or aseptate (so multinucleated, because cytokinesis did not occur properly. In yeasts, the thallus is generally small, globular, composed of single cells which may have buds. Dimorphic fungi are the third type of fungi basing on morphological classi cation, and they present yeastlike and moldlike thalli in response to environmental conditions such as temperature or CO2 concentration. Dimorphic fungi are mostly pathogenic: in the environment, when the temperature is Lower than 30 degrees celsius, they form hyphae and then from these hyphae spores; the spores later on migrate inside humans (where the temperature is 37 degrees celsius) and here they form budding yeast cells Hyphae form a tangled mass called mycelium, which can be subterranean and enormous. In fact, the so called mushrooms are actually the reproductive structure of molds and a small visible extension of vast underground micelia. I fi fi . NUTRITION OF FUNGI Fungi acquire nutrients through absorption upon secreting catabolic enzymes that brake large organic molecules in the environment. Most are saprobes: they absorb nutrients from the remnants of dead organisms. Most fungi are aerobic, whereas many yeasts are facultative anaerobes and they obtain energy from fermentation. Anaerobic fungi can be found in the digestive tract of herbivores and there they contribute to catabolism of plant material. Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé REPRODUCTION IN FUNGI All fungi have some means of asexual reproduction involving mitosis and cytokinesis, but actually most of them reproduce also sexually. Asexual and sexual reproduction occur in a di erent way. ASEXUAL REPRODUCTION It can occur through budding or spores formation. During asexual reproduction, yeasts bud in a way which is pretty similar to prokaryotes. Some of them (such as candida albicans) produce a long lament called a pseudohypha (several buds remain attached) which can invade tissues penetrating intercellular cracks. Filamentous fungi produce lighwight spores that travel long distances. Di erent types of spores can form: sporangiospores form inside a sac called sporangium born on a stalk (sporangiospore). Chlamidospores form inside hyphae. Conidia are produced on the tips of hyphae. SEXUAL REPRODUCTION It occurs through the formation of spores. In the image, the mating types have been marked with a plus or a minus since the thalli are all identical. The reproductive process occurs in four steps: 1) Haploid(n)cells from a +and – thallus fuse forming a dikaryon (n+n) with 2 nuclei, 2) After hours-years-centuries, the two nuclei fuse forming a diploid (2n) nucleus, 3) Meiosis occurs, and the fungus is in its haploid state, 4) Generation of + and – spores, 5) Mitosis takes place: generation of + and – thalli. fi ff ff In case of limited nutrients availability and unfavourable conditions, fungi tend to prefer sexual reproduction. Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé CATEGORIES OF FUNGAL AGENTS Fungi are divided into true fungal pathogens and opportunistic fungi. Only four fungi are usually considered true pathogens, whereas other fungi are opportunistic. Certain factors increase the risk of opportunistic mycoses, such as having undergone an invasive medical procedure such as surgery, medical therapies (immunosuppressive drugs, radiation, chemotherapy, antibiotics), certain diseases (immune defects, leukemia, diabetes, AIDS, chronic illnesses), speci c lifestyle problems such as malnutrition and poor hygiene. True pathogens are endemic mainly in the americas, whereas opportunistic fungi are distributed all around the world and infection a ect individuals with a poor immune defense. OPPORTUNISTIC FUNGI AND MYCOSES Mycoses can be either systemic or cutaneous/subcutaneous; they are acquired via inhalation, trauma or infection. Most of them are not contagious, and epidemics occur as a result of mass exposure to some environmental source of fungi. Dermatophytes are contagious and transmitted via fomites. Some species of candida and pneumocystis can be transmitted by contact. CLASSIFICATION OF FUNGI Fungi can be classi ed in three categories: zygomycota, ascomycota, basidiomycota, deuteromycetes. fi ff fi fi fi ZYGOMYCOTA There are 1100 known species of zygomycota, most of them are saprobes (feed on decomposing substances) and others are obligate parasites of insects or other fungi. Some zygomycota cause opportunistic infections in humans (such as Mucor), they reproduce asexually through sporangiospores. Microsporidia are a division of zygomycota that were once classi ed as protozoa, and then rede ned after genetic analysis. They are obligate intracellular parasites. They spread around in the environment as resistant spores and there are seven genera causing disease in immunocompromised patients, including Nossema, Encephalitozoon, Microsporidium. Encephalitozoon intestinal, for example, causes diarrhoea in HIV-infected patients. Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé LIFE CYCLE OF RHIZOPUS (BREAD MOLD), A ZYGOMYCETE This organism can reproduce both via sexual and asexual cycles. During the asexual cycle, the fungus reproduces via sporangiospores that germinate and produce hyphae. In the sexual cycle, the tips of + and - hyphae sure and form a diploid zygosporangium that matures, undergoes meiosis, germinates and produces a sporangium containing haploid sporangiospores, which germinate to form new mycelia. ASCOMYCOTA There are 32.000 known species of molds and yeasts, ascomycetes form ascospores in a sac called ascus or reproduce by conidiospores. They include most of the fungi spoiling food, but some other infect plants (claviceps purpurea) and humans. The ones a ecting human beings are either true pathogens or opportunistic (aspergillum fumigates, histoplasma, candida, dermatophytes…). Many ascomycota on the other hand are bene cial, such as penicillium and saccharomyces. LIFE CYCLE OF PENICILLIUM, AN ASCOMYCETE BASIDIOMYCOTA There are 22.000 known species of basidiomycota. They produce mushrooms and basidiocarps, other fruiting bodies. They a ect humans by causing decomposition and returning nutrients to the soil, by producing toxins or hallucinatory chemicals, by causing crop damage. The leading cause of fungal meningitis is a yeast called cryptococcus neoformans. LICHENS They are a union between fungi and photosynthetic microbes: the fungi provide nutrient, water and protection; whereas the microbe provides carbohydrates and oxygen. ALGAE They are simple, eukaryotic phototrophs, and they carry out oxygenic photosynthesis using chlorophyll. ff ff ff fi WATER MOLDS They are di erent from fungi, decompose animals and return nutrients to the environment. Some species are pathogens of crops. One species, phytophora infestance, caused the potato famine in Ireland. Still, they are not pathogenic for humans. Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé PARASITIC HELMINTHS AND VECTORS 1. Parasitic worms (helminths) have microscopic infective and diagnostic stages (eggs and larvae-immature forms-in blood, faces, urines. 2. Arthropod vectors are animals carrying pathogens, and they are both mechanical and biological vectors since they can host microbial pathogens. They are widespread and really di cult to control. fl fl ffi HELMINTHIC PARASITES OF HUMANS Helminths are macroscopic, multicellular, eukaryotic worms. They have complex life cycles and at their larval stages they are often inserted in a host. Adult ones are either dioecious (they can be males or females) or monoecious (both sexual organs are on the same worm). There are three groups: 1. Cestodes or tapeworms, which are intestinal parasites; 2. Trematodes or ukes, which are at and leaf-shaped; Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé 3. Nematodes or roundworms, which are long, cylindrical worms, parasites of almost all vertebrates MORPHOLOGY OF A TAPEWORM Tapeworms present a scolex, which is the organ through which they attach to the intestinal wall of the host. They are monoecious so they possess both testes and a uterus. MORPHOLOGY OF FLUKES DISEASE VECTORS BELONG TO TWO CLASSES OF ARTHROPODES I. Arachnida Adult arachnids have four pairs of legs, ticks are the most important arachnid vectors. Ticks are vectors for viral, bacterial and protozoan infections and feed on blood. Some diseases that they can cause are lyme disease (Borrelia), spotted fever (rickettsiosis, Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé arboviruses). A few mite species transmit rickettsial diseases among animals and humans. II. Insecta Adult ones have three pairs of legs and three body regions ( head, thorax, abdomen). Some examples of insects: 1. Fleas: small, vertically attened, wingless. They are mostly associated with rodents, bats, birds; and they feed on blood. They can feed on humans. In cats and dogs they are pests and can serve as intermediate host for a tapeworm (Dipylidium). Rat eas transmit the plague. 2. Lice/louse: horizontally at, wingless. Live in clothing and bedding and move onto humans to feed. Pediculus humanus acts as a vector in epidemic outbreaks of typhus (Rickettsia prowazekii). 3. Flies: di erent species are bloodsuckers and transmit diseases. For example, phlebotomus transmits leishmaniasis, glossina (tsetse y) transmits African sleeping sickness (trypanosoma Bruce). 4. Mosquitoes: female ones feed on blood, they are the most important arthropods in vectoring diseases, they carry the pathogenic causes of malaria, yellow fever, lariasis, dengue fever, viral encephalitis. fl fl fl fl fi ff 5. Kissing bugs: they feed on blood near the mouth of their hosts while they sleep. They cause Chagas’ disease (trypanosoma Cruzi). Sbobinator: Caterina Rocchi Reviewer: Sebastien Wehrlé