Some terms mycology study of fungi mycologists scientists who study fungi mycotoxicology study of fungal toxins and their effects mycoses diseases caused by fungi
100,000 species Only 100 human pathogens, fungi associated diseases are rising, due to nosocomial infections and in immunocompromised patients (ie. HIV, diabetes, transplant folks) Aspergillosis, Blastomycosis—pulmonary infections and dissemination may be involved. 5,000 plant pathogens=$1 billion/yr FUNGI
Fungal Characteristics Eukaryotic Most are Multicellular and some are unicellular. Heterotrophic Absorb nutrients - may be saprobes (absorb from dead material), parasites, or mutualistic symbionts (with algae make lichen). Secrete powerful hydrolytic enzymes. Cell walls contain chitin, an amino sugar polysaccharide also found in arthropod exoskeletons Lack flagella
Characteristics of fungi A. eukaryotic, non- vascular organisms B. reproduce by means of spores (conidia), usually wind-disseminated C. both sexual (meiotic) and asexual (mitotic) spores may be produced, depending on the species and conditions D. typically not motile, although a few (e.g. Chytrids) have a motile phase. E. like plants, may have a stable haploid & diploid states F. vegetative body may be unicellular (yeasts) or multicellular moulds composed of microscopic threads called hyphae. G. cell walls composed of mostly of chitin and glucan. H. Complex cytoplasm with internal organelles, microfilaments and microtubules
H. fungi are heterotrophic ( “other feeding,” must feed on preformed organic material), not autotrophic ( “self feeding,” make their own food by photosynthesis). - Unlike animals (also heterotrophic), which ingest then digest, fungi digest then ingest. -Fungi produce exoenzymes to accomplish this I. Most fungi store their food as glycogen (like animals). Plants store food as starch. K. Fungal cell membranes have a unique sterol, ergosterol, which replaces cholesterol found in mammalian cell membranes L. Tubule protein—production of a different type in microtubules formed during nuclear division. M. Most fungi have very small nuclei, with little repetitive DNA. N. Mitosis is generally accomplished without dissolution of the nuclear envelope
Introduction of fungi Eukaryotic, Heterotrophic (chemoheterotrophic) microorganism No chlorophyll, non-motile Thread of cells (hyphae), transverse cell walls (septate), hyphal anastomosis Storage compound; glycogen
Molds filamentous fungi hyphae (s., hypha) the filaments of a mold may be coenocytic (no cross walls) or have septa (cross walls) mycelium (pl. mycelia) bundles or tangled masses of hyphae
Yeasts unicellular fungi reproduce asexually, often by budding reproduce sexually by formation of spores
Hyphae Hyphae are designed to increase the surface area of fungi and thus facilitate absorption May grow fast, up to 1 km per day, as they spread throughout a food source May be coenocytic, having no septa between cells, or septa may be present with pores through which cytoplasm can flow moving nutrients through out the fungus Parasitic fungi have modified hyphae called haustoria, which penetrate the host tissue but remain outside cell membrane
The Body of a Fungus Fungi exist mainly in the form of slender filaments (hyphae). long chains of cells joined end-to-end divided by cross-walls (septa) rarely form complete barrier cytoplasm freely streams in hyphae mycelium - mass of connected hyphae grows through and penetrates substrate
MYCELIUM Intertwined filamentous mass formed by hyphae, visible to the unaided eye Forms when environmental conditions are right Vegetative mycelium: Mycelial portion remaining INSIDE the substrate to obtain nutrition Reproductive mycelium: Mycelial portion extends into air,responsible for SPORE reproduction
Introduction of fungi Other characteristics of fungi the ability to synthesize lysine by the -amino adipic acid pathway (AAA-pathway) possession of a chitinous cell wall plasma membranes containing the sterol ergosterol and microtubules composed of tubulin.
Fungal wall Shape of fungi Protect against osmotic lysis It the wall contains pigments (melanin) protect the cell against ultraviolet radiation or the lytic enzymes of other organisms It can have antigenic properties
Cell wall components Predominance of polysaccharides, lesser amounts of proteins and lipids
Cell wall components The major polysaccharides of cell wall matrix consist of glucans such as manans, chitosan, and galactans Glucan refers to a group of D-glucose polymers having glycosidic bonds Insoluble -glucans are apparently amorphous in cell wall Mannans, galactomannans, rhamnomannans are responsible for the immunologic response to the medically important yeasts and molds
Cell wall components Consisting of chitinous microfibrils embedded in the matrix of small polysaccharides, proteins, lipids, inorganic salts, and pigments Chitin is a ( 1-4)-linked polymer of N-acetyl-D- glucosamine (GlcNAc) Produced in cytosol (from UDP GlcNAc into chains of chitin by chitin synthetase) The chitin microfibrils are transported to the plasmalemma and subsequently integrated into the new cell wall
Cell wall components In addition to chitin, glucan, and mannan, cell walls may contain lipid, protein, chitosan, acid phosphatase, amylase, protease, melanin, and inorganic ions (phosphorus, calcium, and magnesium) The outer cell wall of dermatophytes contains glycopeptides that may evoke both immediate and delayed cutaneous hypersensitivity
Plasma membrane The main role of the plasma membrane To regulate the uptake and release of materials Integral membrane protein (chitin syntase, glucan syntase) Signal transduction
Plasma membrane Similar to mammalian plasma membrane, differing in having the nonpolar sterol ergosterol, rather than cholesterol regulates the passage of materials into and out of the cell by being selective permeable Several antifungal agents interfere with ergosterol synthesis (i.e., amphotericin B)
Microtubules Composed of the protein tubulin, which consists of a dimer composed of two protein subunits. Microtubules are long, hollow cylinders ~ 25 nm in diameter Involved in the movement of organelles, chromosomes, nuclei, and Golgi vesicle containing cell wall precursor
Microtubules Assist in the movement of chromosomes during mitosis and meiosis the destruction of cytoplasmic microtubules interferes with the transport of secretory materials to the cell periphery, which may inhibit cell wall synthesis
Nucleus The nucleus is bounded by a double nuclear envelope and contains chromatin and a nucleolus Fungal nuclei are variable in size, shape, and number The number of chromosomes varies with the particular fungus S.cerevisiae ; 18 (n) T.mentagophytes ; 4 (n)
The growth of hyphae Apical extension Balance between wall synthesis and wall lysis The apical vesicles are produced from Golgi bodies and then transported to the tip Spitzenkörper (apical body)
The vesicles fuse with the plasma membrane at the tip, and release their contents. enzymes involved in wall synthesis, (chitin syntase, glucan synthase) enzymes involved in wall lysis, enzyme activators, some preformed wall polymers such as mannoproteins
Physiology Aeration Nutrition Water Temperature Hydrogen ion Light
Aeration The fungi include species that are obligately aerobic (eg. most Zygomycota), obligately anaerobic (eg. rumen fungi) Organisms can obtain energy by oxidative (respiratory) metabolism or by fermentation O 2 is used for oxidative metabolism to generate energy. However it is essential for biosynthesis of sterols, unsaturated fatty acids and some vitamins
Table 2 Energy metabolism in relation to O 2 requirements Obligately oxidative. Obligate aerobes. Exp. Rhodotorula Facultatively fermentative. Energy can be obtained by oxidative and fermentative processed such fungi are likely to be faculative anaerobes. Oxidative metabolism, provides much more energy than fermentative, so higher yields can occur under aerobic conditions. Exp. Mucor, Saccharomyces Obiligately fermentative. Oxygen is not needed for energy production, may be either harmless or toxic. Exp. Blastocladia, Neocallimastix
Diagrammatic representation of the mixed-acid fermentation of the rumen chytrid Neocallimastix. Part of the fermentation occurs in the cytosol and hydrogenosome Hydrogenosome: functionally equivalent to the mitochondria of aerobic organisms
Fungal nutrition A. Absorptive mode over whole surface or via restricted absorbing regions, e.g. a. rhizoids in "lower" fungi b. substrate hyphae* in "higher" fungi c. apical tips of hyphae *The substrate hyphae of molds nourish the aerial hyphae and reproductive hyphae B. Extracellular digestion Fungi secrete enzymes that depolymerize complex natural products (proteins, carbohydrates, lipids, etc.) so they can be absorbed as sources of carbon and energy.
The nutrient requirement of fungi Carbon needs for the synthesis of carbohydrates, lipids, nucleic acids, and proteins. Simple sugars, polysaccharides, citric acid, glycerol Nitrogen for synthesis of amino acids for proteins, purines and pyrimidines for nucleic acids, glucosamine for chitin, and various vitamins Amino acid, ammonium, nitrate
Nutrition C/N ratio (20:1) Other elements P : energy-rich compound metabolism, phospholipid in lipid bilayer K : coenzyme Mg : concer with sporulation S : protein component Trace elements Fe, Cu, Mn, and Zn
Czapek-Dox medium widely used for the culture of fungi Mineral base: C and energy source: N source: Water: If a solid medium is required: KH 2 PO 4 MgSO 4.7H 2 O KCl FeSO 4.7H 2 O Sucrose (Glu,starch) NaNO 3 Agar 1 g 0.5 g 0.01 g 30 g 2 g 1 litre 20 g
Water availability Most fungi require very high water availability (relative humidity), and rapidly dry out or senescence in dry conditions. Water activity (a w ) = p s /p w (pure water = 1) DNA is denatured at a w = 0.55 Osmophiles 0.85, Xerophiles 0.80, Halophiles 0.75 The xerotolerant fungi can grow slowly, at water activity of 0.64.
CLASSIFICATION Fungi are eukaryotic organisms that do not contain chlorophyll, but have cell walls, filamentous structures, and produce spores. These organisms grow as saprophytes and decompose dead organic matter. There are between 100,000 to 200,000 species depending on how they are classified. About 300species are presently known to be pathogenic for man. There are five kingdoms of living things. The fungi are in the Kingdom Fungi.
KINGDOM CHARACTERISTIC EXAMPLE Monera Prokaryocyte Bacteria Actinomycetes Protista Eukaryocyte Protozoa Fungi Eukaryocyte * Fungi Plantae Eukaryocyte Plants, Moss Animalia Eukaryocyte * Arthropods Mammals Man *This common characteristic is responsible for the therapeutic dilemma in anti-mycotic therapy.
Medically important fungi are in four phyla: 1.Ascomycota - Sexual reproduction in a sack called an ascus with the production of ascopspores.( Aspergillus, Blastomyces dermatidis, Histoplasma capsulatus) 2.Basidiomycota -Sexual reproduction in a sack called a basidium with the production of basidiospores.( Cryptococcus neoformans) 3.Zygomycota - sexual reproduction by gametes and asexual reproduction with the formation of zygospores.( Rhizopus, Mucor) 4.Deuteromycota(Fungi Imperfecti \Mitosporic Fungi) - no recognizable form of sexual reproduction. Includes most pathogenic fungi ( Sporothrix, Coccidioides immitis, Candida, Pneumocystis).