Fungi and Parasites Flashcards
What is fungi
- Nutritional Requirements: Chemoheterotroph (organic compounds for energy), absorptive (food acquisition), aerobic / facultative anaerobes, few anaerobic fungi
- Structure: Multicellular, filamentous, fleshy, sexual and asexual spores, no embryo formation, eukaryotic, sterols in cell membrane, glucans, mannans and chitin in cell wall
What are characteristics of fungi and the types / structure of hyphae
- Vegetative Structures: Composed of the cells involved in catabolism and growth
- Moulds and Fleshy Fungi: Thallus (body) consists of long filaments of cells joined together (hyphae)
- Septate Hyphae: Hypha that contain cross-walls called septa, which divide them into distinct, uninucleate units
- Coenocytic Hyphae: Hyphae that lack septa, long continuous hyphae with many nuclei
- Growth: Grow by elongating at their tips, each part of the hypha is capable of growth, if a fragment breaks off it can form a new hypha, can grow to immense proportions
- Portions of Hypha: Mycelium (filamentous mass), vegetative (obtains nutrients), aerial / reproductive (above surface of media, reproduction)
What are yeasts
- Structure: Unicellular fungi, non-filamentous, spherical / oval shape, widely distributed,
- Nutritional Requirements: Facultative anaerobes
- Budding: Divide unevenly, parent forms protuberance, nucleus divides, bud breaks away, failure of bud to detach causes pseudo-hypha (Saccharomyces)
- Fission: Divide evenly, elongation of cell, division of nucleus, two daughter cells, facultative anaerobic growth (Schizosaccharomyces)
What are dimorphic fungi
- Dimorphism: Pathogenic spp. of fungi, two forms of growth
- Mould-like forms produce vegetative and aerial hyphae 25°C
- Yeastlike forms reproduce by budding 37°C
- Morphogenesis: Developmental change, morphological transition, often connected with metabolic flexibility, evolve to adapt to different environments
What is the fungal lifecycle (asexual and sexual spores)
- Fungal Spores: Reproduction, spore detaches from parent and germinates, do not exhibit extreme tolerance and longevity of bacterial endospores
- Asexual: Formed from hyphae of one organism, germinate and genetically identical to parent, less frequently produced
- Sexual: Result from fusion of nucleifrom two opposite mating strains of the same species of fungus
- Telemorphic: Produce both sexual and asexual spores
- Anamorphic: Only produce asexual spores
What are asexual spores
- Produced by an individual fungus through mitosis and subsequent cell division, no fusion of nuclei, two types of asexual spores
Conidiospore / Conidia: - Unicellular or multicellular spore that is not enclosed in a sac, produced at the end of a chain of a conidiosphore (Penicillium / Aspergillus)
- Arthroconidia: Fragmentation of a septate hypha into single, slightly thickened cells
- Blastoconidia: Buds of its parent cell, yeasts
- Chlamydoconidium: Thick-walled spore, rounding and enlargement within a hyphal segment
Sporangiospore: - Within a sporangium, or sac, at the end of an aerial hypha called a sporangiophore
What are sexual spores
- Fungal spore results from sexual reproduction, three phases
1. Plasmogamy: Haploid donor cell nucleus (+) penetrates cytoplasm of recipient cell (–)
2. Karyogamy: (+) and (–) nuclei fuse, form diploid zygote nucleus
3. Meiosis: Diploid nucleus produce haploid nuclei (sexual spores)
What are nutritional adaptations of fungi
- Grow better in slightly acidic environments (pH 5)
- Almost all moulds are aerobic, most yeasts are facultative anaerobes
- Resistant to changes in osmotic pressure (survive in high sugar / salt conc.)
- Can grow in very low moisture content areas
- Require less N than bacteria for equivalent amount of growth
- Capable of metabolising complex carbohydrates
What are medically important fungi (4)
Zygomycete:
- Conjugation fungi, coenocytic, produce sporangiospores / zygospores, fusion of haploid nuclei
- Rhizopus and Mucor (opportunistic, systemic mycoses)
Ascomycota:
- Sac fungi, septate, teleomorphic (asexual / sexual spores), ascospores and frequently conidiospores
- Aspergillus (opportunistic, systemic mycosis)
- Blastomyces dermatitidis, Histoplasma capsulatum (systemic mycoses)
- Microsporum, Trichophyton (cutaneous mycoses)
Basidiomycota:
- Club fungi, septate, produce basidiospore / conidiospores, formed externally on pedestal
- Cryptococcus neoformans (systemic mycosis)
Anamorphs:
- Produce asexual spores only, rRNA sequencing places most in ascomycota; few are basidiomycota
- Penicillium, Sporothrix (subcutaneous mycosis)
- Stachybotrys, Coccidioides, Pneumocystis (systemic mycoses)
- Candida albicans (cutaneous mycoses)
Describe fungi as commensal organisms
- Commensalism: Association between two organisms in which one benefits and the other derives neither benefit nor harm, fungi often only seen as pathogens
- Host: Immune system must be tuned to tolerate constant exposure to environmental and commensal fungi, play an important role in the mammalian ecosystem
What are fungal diseases / fungi as pathogens
- Microbiota: Fungi exist as part of the microbiota in mammals at mucosal surfaces, different mechanisms by which fungi can cause infection
- Mucosal damage (increase inflammation, chemicals, physical trauma)
- Use of antibiotics (decrease bacterial microbiome)
- Immune defects (decrease antimicrobial peptides and CD4 T and THI17 cell immunity, significant impact on crops)
What are the economic effects of fungi
- Biotechnology: Aspergillus niger (used to produce citric acid), Saccharomyces cerevisiae (bread, wine, HBV vaccine), Trichoderma (cellulase, clarify fruit juice), Taxomyces (taxol, anti-breast cancer drug)
- Biological Control: Entomophaga (biocontrol of gypsy moths) and Parcilomyces (kills termites)
What are protozoa
- Classification: Protozoan (first animal, animal like nutrition)
- Structure: Unicellular, eukaryotic, embryo formation, produce cysts, cytostome (protective covering)
- Reproduction: Sexual (conjugation) and asexual (binary fission) reproduction
- Encystment: Produce a protective capsule (cyst), permits survival in extreme conditions, survival outside host
- Nutritional Requirements: Aerobic heterotrophs, intestinal protozoa (anaerobic growth), photosynthesise to generate energy, chemoheterotroph
- Amoebas engulf food by surrounding itself with pseudopods and phagocytising
- Environment: Large water supply, inhabit soil and water, ingestive and absorptive
What are pathogenic protozoa
Archaezoa:
- No mitochondria (fermentation of glucose / AA arginine), multiple flagella
- Giardia lamblia (diarrhoea) and Trichomonas vaginalis
Microspora:
- No mitochondria, non-motile, intracellular parasite, Nosema
Amoebozoa:
- Move by pseudopods (blunt, lobe-like projections of cytoplasm)
- Entamoeba histolytica, Acanthamoeba (water)
Apicomplexa:
- Nonmotile in mature forms, obligate intracellular parasites, complex life cycles
- Plasmodium (malaria, complex lifecycle = difficult to generate a vaccine), Babesia (infects RBCs), Cryptosporidium / Cyclospora (diarrhoea)
Talk about malaria and plasmodium
- Protist disease caused by Plasmodium spp.
- Complex life cycle that includes Anopheles mosquitos as vectors
- Generally found in tropical and subtropical regions
