MYCOVIRO LEC 1

Fungal cell wall carbohydrates

50-60% carbohydrate polymers (mannans and glucans)

Fungal cell wall chitin

20-40% chitin

Chitin

N-acetyl glucosamine; tough material also found in insect exoskeleton

Two phases of fungi

Yeast phase and mold phase

Yeast phase microscopic appearance

Unicellular organisms

Yeast phase macroscopic appearance

Creamy colonies resembling bacterial colonies

Example yeast phase

Candida albicans

Mold phase microscopic appearance

Multicellular

MYCOLOGY

Is the study of fungi

Fungi characteristics

Thallophytes; achlorophyllous; aerobic; nucleated; true cell wall; reproduce sexually and/or asexually

Thallophytes

Group of plants or plant-like organisms that lack differentiated stems, leaves, and roots

Achlorophyllous

Cannot produce chlorophyll, not dependent on light, can occupy dark habitats

Respiration of fungi

Aerobic

Fungal reproduction

Reproduce sexually and/or asexually

Nucleated fungi

Classified as eukaryotes with true nucleus enclosed by nuclear membrane

True cell wall

Present in prokaryotes (algae) and eukaryotes (plants) but absent in animals

Fungal cell wall vs plants

Cell walls of fungi are not made of cellulose like plants

Fungal cell wall protein

5-10% protein

Mold phase macroscopic appearance

Cottony mycelial colonies

Example mold phase

Aspergillus niger

Monomorphic fungi

Fungi that only have one phase regardless of temperature

Monomorphic yeasts

Candida albicans and Cryptococcus neoformans

Characteristic of monomorphic yeasts

Exhibit only yeast phase even at different temperatures

Monomorphic mold

Aspergillus spp.

Characteristic of Aspergillus spp.

Green cottony mold colonies at room temperature and 37°C

Yeasts

Single-celled fungi with thick cell wall

Yeast colony appearance

Moist, creamy, opaque or pasty colonies on media

Asexual reproduction of yeast

Budding or blastoconidia formation

Sexual reproduction of yeast

Production of ascospores or basidiospores

Budding

Process that repeats to form a chain of bud cells

Blastoconidia

Daughter cell from budding; smaller and spherical

Molds

Fungi with tube-like structural units

Hyphae

Basic structural units of molds

Mycelium

Loose network formed when hyphae intertwine

Function of mycelium

Penetrates substrate to obtain nutrients

Examples of substrate

Tree trunk, loaf of bread, or culture media

Parts of mycelium

Vegetative portion (thallus) and reproductive/aerial part

Vegetative portion / Thallus

Body of fungus that grows in/on substrate and absorbs water and nutrients

Reproductive or aerial part

Contains fruiting bodies that produce conidia or spores

Septate hyphae

Have cross walls or septum and branch at acute angles

Appearance of septate hyphae

Segments separated by septum compared to continuous nonseptate hyphae

Stain for septate hyphae

Lactophenol cotton blue

Subdivision of septate hyphae

Dematiaceous and hyaline

Dematiaceous hyphae

Dark, pigmented hyphae that produce melanin giving brown color on agar

Hyaline hyphae

Non-pigmented, colorless or transparent hyphae in culture

Nonseptate / coenocytic hyphae

No cross walls; wider diameter

Branching of nonseptate hyphae

Branching at angles greater than 45° up to 90°

Fungi with nonseptate hyphae

Zygomycetes

Sexual reproduction in fungi

Alternation between karyogamy and meiosis

Karyogamy

Nuclear fusion during sexual reproduction

Meiosis

Reduction division of two fertile cells

Perfect fungi

Fungi that exhibit a sexual phase

Asexual reproduction in fungi

Strictly by mitosis; most common process of spore production

Imperfect fungi / Fungi imperfecti

Fungi that only exhibit asexual reproduction

Specialized sexual spores

Basidiospores, ascospores, zygospores, oospores

Basidiospores

Born in a club-shaped basidium; usually up to 4 spores

Basidium

Club-shaped structure bearing basidiospores

Basidiocarp

Fruiting body containing basidium and basidiospores; commonly a mushroom

Location of basidium in mushroom

Gills under the cap

Germ tube

Tubular elongated outpouching without constriction at base

Germ tube significance

Initial stage of true hyphae formation

Microscopic germ tube appearance

Tubular outpouching attached to mother cell without basal constriction

Pseudohyphae

Elongated buds that fail to separate forming sausage-like chains

Pseudohyphae characteristic

Have cell wall constrictions rather than true septations

Ascospores

Contained in saclike ascus; usually 4-8 spores

Ascus

Saclike structure containing ascospores

Ascocarp

Fruiting body enclosing ascus and ascospores

Zygospores

Formed by fusion of two identical cells from same hypha

Oospores

Formed by fusion of cells from two separate non-identical hyphae

Specialized asexual spores

Sporangiospores and conidia

Sporangiospores

Born inside a sporangium

Sporangium

Structure produced on sporangiophore that contains spores

Sporangiophore

Specialized hyphae that produces the sporangium

Release of sporangiospores

Occurs when sporangium ruptures or dissolves

Fungi producing sporangiospores

Zygomycetes (e.g., Rhizopus)

Conidia / conidiospores

Asexual spores produced by conidiophore

Conidiophore

Vegetative hyphae producing conidia

Phialides

Flask or vase-shaped projections that produce conidia

Conidiogenesis

Formation of conidia

Blastic conidiogenesis

Parent cell enlarges, septum forms, enlarged portion splits to form daughter cell; conidia develop before cross wall

Thallic conidiogenesis

Septum forms first, then new growth beyond septum becomes daughter cell

Macroconidia

Large, usually septate, club/oval/spindle shaped; thick or thin wall; smooth or spiny surface

Microconidia

Small, unicellular; round, elliptical or piriform shape

Fusiform conidia

Spindle-shaped with hooked or pointed ends (Microsporum canis)

Clavate conidia

Club-shaped with rounded ends (Epidermophyton floccosum)

Muriform conidia

Multiseptate with transverse and longitudinal septa; hand-grenade appearance (Alternaria)

Sessile and lateral conidia

Develop directly on side of hypha without conidiophore

En grappe conidia

Conidia arranged in clusters

Pedunculate conidia

Develop from the end of a short conidiophore

OLIDIA

Formed when hyphal cells separate to create flat-ended asexual spores

Chlamydospore

Thick-walled resistant resting spores

Formation of chlamydospores

Terminal hyphal cells enlarge and develop thick walls in nutrient-poor conditions

Function of chlamydospores

Germinate into new organism when environmental conditions become favorable

Terminal chlamydospore

Formed at the hyphal tip

Sessile chlamydospore

Formed on the side of the hyphae

Intercalary chlamydospore

Formed within the hyphal strand

Arthrospores / Arthroconidia

Formed by simple fragmentation of mycelium at septum into cylindrical or cask-shaped spores

Cause of arthrospore fragmentation

Wind, soil movement, or insects

Structure of arthrospores

Thick-walled cylindrical or cask-shaped spores

Arrangement of arthrospores

Adjacent or alternate