Taxonomy, biology and physiology of fungi

1. Taxonomy, biology and physiology of fungi

2. Objectives • Introduction of fungi • Biology of fungi • Cell structure, growth and development • Physiology of fungi • Nutrition, Temp, UV light, and water • Classification of fungi

3. Introduction of fungi • Eukaryotic, Heterotrophic (chemoheterotrophic) microorganism • No chlorophyll, non-motile • Thread of cells (hyphae), transverse cell walls (septate), hyphal anastomosis • Storage compound; glycogen

4. 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.

6. Structure • Cell wall • Plasma membrane • Microtubules • Nucleus

7. 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

8. Cell wall components • Predominance of polysaccharides, lesser amounts of proteins and lipids

9. Division Oomycota Chytridiomycota Zygomycota Ascomycota/ deuteromycota Basidiomycota Table 1Major polysaccharide components of fungal walls Fibrillar components Cellulose, (1,3)- (1,6)-glucans Chitin, glucan Chitin, chitosan Chitin, (1,3)-(1,6)- glucans Chitin, (1,3)- (1,6)- glucans Matrix components Glucan Glucan Polyglucoronic acid, glucuronomannoproteins -(1,3)-Glucan, galacto- mannoproteins ,,

10. Cell wallcomponents • 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

11. 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

12. 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

13. 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

14. 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)

16. 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

17. 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

18. 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)

19. The growth of hyphae • Apical extension • Balance between wall synthesis and wall lysis • The apical vesicles (Spitzenkörper) are produced from Golgi bodies and then transported to the tip Spitzenkörper (apical body)

20. 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

21. Hyphal anastomosis • Vegetative hyphal fusion in common in higher fungi • Involves the growth of hyphae toward each other

22. Physiology • Aeration • Nutrition • Water • Temperature • Hydrogen ion • Light

23. 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 • O2is used for oxidative metabolism to generate energy. However it is essential for biosynthesis of sterols, unsaturated fatty acids and some vitamins

24. Table 2 Energy metabolism in relation to O2 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

25. 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

26. The nutrient requirement of fungi • Carbonneeds 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

27. 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

28. Nutrition

29. Czapek-Dox mediumwidely used for the culture of fungi Mineral base: Cand energy source: N source: Water: If a solid medium is required: KH2PO4 MgSO4.7H2O KCl FeSO4.7H2O Sucrose (Glu,starch) NaNO3 Agar 1 g 0.5 g 0.5 g 0.01 g 30 g 2 g 1 litre 20 g

30. Wateravailability • Most fungi require very high water availability (relative humidity), and rapidly dry out or senescence in dry conditions. • Water activity (aw) = ps/pw (pure water = 1) • DNA is denatured at aw = 0.55 • Osmophiles 0.85, Xerophiles 0.80, Halophiles 0.75 • The xerotolerant fungi can growslowly, at water activity of 0.64.

31. Temperature

32. Hydrogen ion • Opt. pH 5.0-7.0 • Acid-tolerant (pH 2.0) Aspergillus, Penicillium, Fusarium, yeast in stomach of animals • Strongly alkaline environment (pH 10-11)  F.oxysporum, P.variabile

33. Light • Influence on fungal growth in specific cases • light does not play a major part in growth and metabolism of fungi • A common metabolic effect of light is the induction of carotenoid biosynthesis

34. Morphology Yeast • Unicellular, round or oval, size 8-15 x 3-5 µm • Conidiogenesis (budding, binary fission, sexual spores) Budding yeasts Binary fission

36. Morphology Mold • Multicellular, hyphae, septate & nonseptate, hyaline & dematiaceous, diameter 4-20 µm • Sexual and asexual reproduction Hyaline septate hyphae Dematiaceous septate hyphae Hyaline aseptate hyphae

37. Morphology Dimorphic fungi (thermally dimorphic fungi) Environment/Routine culture media (SDA) 25-300C ---Mold form Tissue/Enriched media (BHI) 35-370C---Yeast form Sporothrix schenckii

38. Morphology

40. Classificationof fungi • Kingdom Fungi • Division -mycota • Subdivision -mycotina • Class -mycetae • Subclass -mycetes • Order -ales • Family -aceae • Genus -------- • Species --------

41. Classification of fungi • Four major division of fungi, base on the type ofsexual spores (ascospore, basidiospore, zygospore, oosore), plus another group, which have no know sexual state. • Ascomycota • Basidiomycota • Zygomycota • Chytridiomycota • Deuteromycota (Imperfect fungi)

42. Sexual reproductive structures, which are referred to as teleomorphs • reflect phylogenetic relationships because they are based upon structures that form following meiosis • Asexual reproductive structures, which are referred to as anamorphs • does not reflect phylogenetic relationships

43. For example, the dimorphic fungusBlastomyces dermatitidis • Anamorph : hyphae, conidia at 250C and budding yeast cell at 370C • The name B.dermatitidis summarizes these two anamorphs • Teleomorph : sexual fruiting body, called a gymnothecium, containing ascospores • The name that is used for this sexual form or teleomorph is Ajellomyces dermatitidis

44. Sexual reproduction Gametes or gametic nuclei (n) n (monokaryon) n (haploid) Meiosis Plasmogamy (cell fusion) n+n (dikaryon) 2n (diploid) Karyogamy (nuclear fusion) Zygote (2n)

45. Division Ascomycota • Common name: Sac fungi • Sexual reproduction: ascospore in ascus • Asci may form in fruiting body called an ascocarp • Gymnothecium, Cleistothecium, Perithecium, Apothecium • Asexual reproduction: conidia, arthospore, budding • septate hyphae or yeast • Eurotium (Aspergillus)., Arthroderma (Trichophyton)

46. Life cycle of ascomycetes Arthospore

48. Cleistothecium Ascocarp Gymnothecium Perithecium Apothecium

49. Life cycle of the yeast Saccharomyces cerevisiae a c b

50. Division Basidiomycota • Common name: Club fungi, mushroom • Sexual reproduction: basidiospore • Asexual reproduction:budding • hyphae with dolipore septum or yeast • clamp connection • Mushroom: basidiocarp, fruiting body • Filobasidiella neoformans (no basidiocarp) or Crytococcus neoformans