Fungal lectures Flashcards
no of fungal species and class
250,000 species but only 180 cause disease in humans or animals.
most fungi are saphrophytes that feed on dead plant or animal materail.
eukaryotic characteristics of fungi
1 - membrane bound nucleus with several chromosomes
2 - genomic DNA with introns
3 - plasma membrane and cytoplasmic organelles
4 - membranes contain ergosterols
fungal structure
cell wall - predominantly polysaccharides- inner layer of chitin microfibrils, outer matrix of glucans with mannose containing proteins embedded in the cell wall. some yeasts also have a discrete outer polysaccharide capsule.
2 - cytoplasmic membrane, cytoplasm, organelles, nucleus
primary fungal morphologies
1 - yeasts
2 - filamentous moulds
3 - dimorphic fungi
decribe yeast morphology
1 - oval or round unicellular organisms
2 - multiply by mitosis, either by symmetrical binary fission (schizosaccharomyces pombe) or asymmetrical budding (candida, cryptococcus)
3 - some also grow as short cylinders called pseudohyphae (candida)
describe filamentous mould morphology
1 - thin branching multicellular cylinder = a hypha (plural is hyphae)
2 - apical growth, mitosis only occurs at the tip and at side branches
3 - can either be septate with multiple interconnected compartments (aspergillus) or aseptate with many nuclei in a common cytoplasm (mucor)
4 - can form an interwoven mass called a mycelium. when compacted together, layers of hyphae can form fungal tissue in macroscopic structures eg muschrooms.
describe dimorphic fungi morphology
1 - either a filamentous mould at 22 degreesC in the environment or a yeast at 37degreesC in the body (eg histoplasma)
overview of fungal reproduction - brief
produce spores, small, tough, light fungal cells adapted for dispersal and survival in hostile conditions.
spores can be either asexual or sexual, depending on the state of differentiation of the fungus during production.
asexual state = anamorphic state
sexual = teleomorph state
asexual spores - mech of production, examples and function
1 - anamorphic state fungus (asexual/mitotic/imperfect state). produced by mitosis.
2 - yeasts produce internal endospores
3 - moulds produce either external spores = condida/condidium, or internal spores within a sporangium.
4 -asexual spores are for dispersal - germination - multiplication and so colonization.
5 - Deuteromycota group of fungi always exist in the anamorphic state and are incapable of sexual reproduction.
sexual spores - mech of production, examples and function
1 - teleomorphic state (meiotic/sexual/perfect state). most fungi exist in a haploid state and will only briefly produce diploid fungi through this sexual reproduction.
2 - sexual structures are produced (motile gametes/specialized sexual hyphae). those from 2 seperate individuals fuse, nuclei fuse to make diploid - chromosome reassortment and recombination - meiotic reduction division to haploid sexual spores.
4 - usually tough and enable organism survival in hostile conditions. germinate once favourable conditions return.
method of fungi classification (no details) and where are sexual spores formed?
classified by where the sexual spores are formed. either:
1 - internally in tubular structure called an ascus
2 - externally on a specialised club-like structure called a basidium
3 - or externally as a thick walled structure following fusion of the sexual hyphae.
classify fungi
1 - broken down into yeasts, filamentous moulds and dimorphic fungi. each of these can divided into ascomycota, basidiomycota, zygomycota and deuteromycota.
2 - so, structure and reproduction.
3 - ascomycota = both sexual and asexual spores. sexual in an ascus, asexual externally as a conidium.
4 - basidiomycota - only sexual spores, externally on a basidium.
5 - zygomycota - both sexual via external fusion of hyphae, and asexual internally in a sporangium
6 - deuteromycota (imperfect fungi) - no sexual spores, asexual spores produced externally
examples of ascomycota?
yeasts - schizosaccharomyces, saccharomyces, pneumocystis, candida
moulds - aspergillus, fusarium, microsporum, trichophyton, epidermophyton.
dimorphic - histoplasma
examples of basidiomycota?
yeasts - cryptococcus, malassezia
examples of zygomycota
moulds - mucor and rhizopus
examples of deuteromycota
dimorphic - coccidioides, paracoccidioidea, sporothrix.
how do fungi feed?
secrete enzymes into environment to digest food material, absorb simple molecules through cell wall pores. live in moist environments. hyphae penetrate food material.
what are the different lifestyles of fungi?
1 - saprotrophs - feed on dead plants and animals, occasionally cause disease is accidentally implanted of inhaled
2 - parasites of living plants - makor cause of crop disease (ergot?)
3 - parasites of humans and animals, can cause disease.
what 6 metabolites produced by fungi are of interest to us?
1 - CO2 - raising bread dough
2 - ethanol - alcoholic drinks
3 - antibiotics - penicillin, cephalosporin, streptomycin
4 - immunosuppressants - cyclosporin
5 - other drugs - ergotamine, ergometrine
6 - toxins - aflatoxins