Eukaryotic Microbes Flashcards
Prokaryotes versus Eukaryotes
Fungal cell
Typical eukaryotic cell structure, except: • ergosterol instead of cholesterol in plasma membrane (NB also in some protists) • very rarely flagellated • cell wall
• Composed of chitin • long chain polymer of Nacetylglucosamine • beta1,4 linkages • synthesised by chitin synthase (usually multiple paralogues in a genome)
Fungal lifestyles
• Always yeast (Saccharomyces cerevisiae) • Always hyphal (Agaricus bispora) • A mixture (Candida albicans) • Reproduction is often asexual • hyphal spread • single cell budding • asexual spores
Sexual reproduction in fungi • A nightmare!! • Classical mating involves • two mating types (alpha and a, or minus and plus), which can sometimes switch • fusion results in diploid cell that undergoes meiosis to generate haploid recombinants
for many fungi, sexual states are not known • often diploids and haploids are both stable • the morphology of mating is highly variable • mycologists give different names to the two states: • anamorphs (asexual/imperfect) & teleomorphs (sexual/perfect) • these can have different binomials, e.g. • Cryptococcus neoformans (yeast) = Filobasidiella neoformans (hyphal)
Algae
Three groups of algae: red, green and brown • brown algae are all multicellular (= seaweed), highly derived species that arose through secondary endosymbiosis • NB: ‘blue-green algae’ are not algae, but bacteria, and correctly known as cyanobacteria
Red Algae
• Some unicellular, many multicellular • Often, but not always, red - due to phycoerithrin (an ‘accessory’ pigment) • Typically marine (but some freshwater)
Green algae
Some unicellular, many multicellular • Typically freshwater (but some marine) • Evolutionarily very important as: • the ancestor of plants • an insight into the evolution of multicellularity (Volvox
Protists
A polyphyletic (and very messy!) group • Loosely defined as “unicellular eukaryotes without a cell wall”, but no shared defining feature • “Protozoa” is sometimes used interchangeably, but sometimes as a subgroup (the most ‘animaly’ protists)
No unifying morphological or biochemical feature for all protists • But within the protists, different groups are frequently characterised by a unique, shared character
Fungal Nucleus
Double membrane bound organelle ranging in size from 1-2 µm to 20-25 µm in diameter • Ploidy • most fungi haploid with 6-20 chromosomes • some fungi naturally diploid • Others alternate between haploid and diploid • Unique features of fungal nuclei • Membrane remains intact during mitosis • No clear metaphase plate
Fungal Cytoplasmic Organelles
Plasma membrane - phospholipid bilayer • Anchorage for enzymes/proteins such as chitin synthases or glucan synthases • contains ergosterol • Chitosomes • microvesicles for chitin synthesis
The Fungal Cell Wall
Structural Barrier • Environmental interface • Protects against osmotic lysis • Contains pigments for protection • Binding site for molecules • Mediates interaction with other organisms
Mannans give fungal cells a detectable signature
Filamentous Fungi
Main structure: Hyphae - rigid tubes containing cytoplasm Interconnected compartments, not individual cells
septate hyphae: joint cells have distinct separations called septa, contain pores
coenocytic hyphae: hyphae consists of fused cells, multinucleated
Filamentous Fungi - Growth
Mass of hyphae = mycelium (plural: mycelia) Vegetative hyphae • grow along the surface • obtain nutrients Aerial hyphae • stick up from the mycelium • spores for reproduction
Hyphae tips show tropism to a variety of sources: light, nutrients, etc
Yeasts
• non-filamentous, unicellular, ovaloid • facultative anaerobes • ferment carbohydrates into alcohol and carbon in absence of oxygen
Budding Yeast • Divide by producing outgrowth called bud • Bud enlarges and separates from mother cell Pseudohyphae are not true hyphae: Hyphae: cells tightly attached by shared walls, cytoplasms joined by pores pseudohyphae: daughter cells remain stuck but do not share cytoplasm
Fission Yeast
• Division by elongation of mother cell and mitosis • Daughter cells separate by formation of septa in the centre e.g Schizosaccharomyces pombe
Dimorphic Fungi
Grow as multicellular hyphal form or unicellular yeast depending on conditions
Several pathogens of humans exhibit dimorphism • Candida albicans • Histoplasma capsulatum • Mucor circinelloides
Dimorphism occurs in response to a variety of environmental factors
- Histoplasma capsulatum • 25°C = filamentous • 37°C = yeast
- Candida albicans • human body = filamentous
- Mucor circinelloides • oxygen = filamentous • hypoxia = yeast
Chytridiomycota
Most primitive fungi Approximately 1,000 species Many chytrids are aquatic The exception - motile zoospores and gametes
Glomeromycota
• Approximately 230 species • Terrestial and widespread • Members form arbuscular mycorrhizas (>80 % plants) • Fungus helps plant to capture nutrients such as phosphor, sulfur and nitrogen • Plant provides carbohydrates
Mucormycota
Approximately 1,000 species Zygosporangium with zygospores Sexual reproduction is NOT common in fungi!!!
Ascomycota
Approximately 65,000 species Ascus with ascospores
Conidiospore: asexual spore formed at end of hyphae called conidiophore; Conidia: chains of conidiospores on conidiophore
Life Cycle - e.g. Saccharomyces cerevisiae - a and alpha mating type - Mating is controlled by the MAT gene locus which is flanked by two other loci - MATa and MATalpha - a copy of one of the flanking loci is inserted into the MAT locus and determines mating type - MAT switching can occur after each budding
Saccharomyces cerevisiae Schizosaccharomyces pombe Neurospora crassa Candida albicans Aspergillus fumigatus
Basidiomycota
• > 30,000 species • Basidium with basidospores • Can form basidiocarp (fruiting body)
Agaricus bisporus Boletus edulis Cantharellus cibarius Amanita muscaria Amanita phalloides Cryptococcus neoformans
The Oomycetes
a protist (diverse group of eukaryotic microorganisms) • distinct lineage • fungal characteristics • heterotroph • morphology (water mold) • but also plant-characteristics • cellulose cell wall • some have chloroplasts
Microsporidia
Originally thought to be primitive protists • But now known to be close sister group to fungi • A derived group (i.e. they have lost many features during evolution) because… • …they are all obligate parasites of animals
Euglenozoans
• Flagellated • characteristic feature is a crystalline rod in flagellum (Why? Nobody knows!) • Two major groups: • Kinetoplastids • Euglenids
two groups
- Kinetoplastids • Contain KINETOPLAST: mass of DNA in a single large mitochondrion • Most important genus for us is Trypanosoma
- Euglenids • Facultatively phototrophic • Lose chloroplast and survive by heterotrophy in the dark
Diplomonads
Two nuclei • Mitosomes (double membrane sacs without electron transport chain) • Most important for us is Giardia intestinalis
An early branching lineage (probably!) • Flagellated and live in anaerobic environments
Alveolates
Characterised by cortical alveoli • function unknown: osmoregulation, secretion? • three important groups: • ciliates • dinoflagellates • apicomplexans
• Ciliates
• all produce cilia, used for motility and often for feeding (e.g. Paramecium) • macro and micro nucleus • anaerobic fermenters in the gut
Alveolates
- Dinoflagellates • two flagella, which drive whirling motion • aquatic and can be: • toxic (“red tides”) • bioluminescent
- Apicomplexans • all are obligate animal parasites • contain degenerate chloroplasts called APICOPLASTS, thought to originate from a red alga [Nair & Striepen, PLoS Biol, 2011] • include major human pathogens Plasmodium, Toxoplasma
Stramenopiles
Grouped based on ‘hairy’ flagella. • Major groups are: • brown algae (multicellular) • golden algae • diatoms (silica cell wall) • oomycetes…
Oomycetes
• previously classified as fungi • filamentous growth, multinucleate hyphae • but • cell wall is cellulose • they are flagellated • diploid phase is dominant • Phytophthora infestans, causes potato blight
Cercozoans & Radiolarians
Unifying feature is threadlike PSEUDOPODIAL movement (but note that amoebozoa do this too!) • some are secondarily phototrophic (chlorarachniophytes) • but most are heterotrophs that produce a shell called a ‘TEST’
Amoebozoa
• Also use PSEUDOPODIAL movement, but via bigger (lobe-like) protrusions • Diverse group, important (to us!) for two reasons: • as pathogens (e.g. Entamoeba) • as cell biology models (e.g. Dictyostelium)
Fungi as infectious agents
MYCOSIS
Primary: virulence factors that enable invasion and grow in healthy host Opportunistic: low virulence, cause of infection in a compromised host (e.g. HIV, cancer, steroid therapy, pregnancy, diabetes)
Superficial > Cutaneous > Subcutaneous > Systemic
Pathogenesis of Mycoses
Infectious agent: spores, hyphal elements and yeasts
Enter body through respiratory, mucous and cutaneous routes - primary pathogens tend to enter via respiratory route
Dermatophytes and Candida sp. part of the human normal flora
Most mycoses not communicable - Exception: Dermatophytes and Candida sp. transmissible
Fungal Diseases
Fungal diseases (mycoses) are often: • superficial, e.g. athlete’s foot (Trichophyton), dandruff (Malassezia) • opportunistic (secondary), e.g. thrush (Candida), cryptococcosis (Cryptococcus) • But serious primary mycoses exist (e.g. Coccidiodes) and boundaries are blurred (e.g. Cryptococcus gattii)
Most common serious fungal infection is candidiasis (Candida albicans, or related sp.) • Commensal on skin/body tracts • Disseminating infection involves a DIMORPHIC SWITCH - yeast to hyphal
Medically important fungi
Primary Pathogens - Histoplasma capsulatum - Blastomyces dermatitidis - Coccidioides immitis - Paracoccidioides brasiliensis
Pathogens with intermediate virulence - Dermatophytes
Opportunistic pathogens - Cryptococcus neoformans - Candida albicans - Aspergillus species - Pneumocystis carinii - Mucormycetes
Euglenozoal Diseases
• Euglenozoa - Crystalline rod in flagellum • Kinetoplastids - mass DNA in single mitochondrion • Trypanosoma
Trypanosomiasis • Parasite is transmitted by invertebrate vector: • Tsetse fly (Glossina sp.) for T. rhodesiense/gambiense • Assassin/kissing bug (Reduviidae) for T. cruzi
Amoebozoal Diseases
Move via extension of lobe-like pseudopods • Human pathogens include Entamoeba histolytica and Acanthamoeba castellani
Entamoeba histolytica • Causes amoebic dysentery • Cysts ‘hatch’ in the intestine • Penetrate the gut wall, causing bloody diarrhoea
Acanthamoeba spp. Free-living amoebae that also produce cysts • Cause serious infection in immunocompromised hosts • Most common presentation is AMOEBIC KERATITIS
Diplomonads & Parabasalids (Diseases)
• Both - amitochondriate • Diplomonads - two nuclei and mitosomes • Parabasalids - parabasal body and hydrogenosomes
Usual transmission is faecal-oral, via contaminated water • Due to the formation of resistant CYSTS • Symptoms (explosive diarrhoea etc.) either a) acute, b) chronic or c) asymptomatic carriage • treatment is metronidazole
Trichomonas • Sexually transmitted (NB - no cysts), causes inflammation and discharge • 25-50% of women are infected. Men are carriers (generally asymptomatically). • treatment is metronidazole
Alveolate Diseases
Include dinoflagellate ‘red tides’ and ciliate parasites, but the big problem are the APICOMPLEXANS • Apicomplexans are ALL obligate parasites • Our selected examples: • Malaria & Toxoplasma
Malaria • Plasmodium species (vivax and falciparum, primarily) • Transmitted by Anopheles mosquitoes • Complex lifecycle with liver stage, blood stage, vector stage
Toxoplasma gondii • Usually asymptomatic, but transmission to foetus is very serious • Humans are accidental hosts
