1. Lecture 2 - The Biology of Fungi
Bio 222b
Lecture 2 - The Biology of Fungi

2. Lecture 2 - The Biology of Fungi
Chromistan fungi - many are unicellular with motile forms - typically live in wet places
diploid somatic cells
Eumycotan fungi - most are filamentous and multicellular - most don’t need wet places
some unicellular (yeasts)
most non-motile
haploid somatic cells

3. Growth of fungi Fungi grow :-
As filaments (hyphae) often massed together (mycelium)
Active part of colony always at the edges (apical growth)

4. Growth of Fungi As budding cells (yeast and yeast-like fungi)
Some fungi alternate between both types (dimorphic)

5. Some fungi (Chromista + Chytrids) have motile forms (possess flagellae) Flagellae have typical structure
2 types of flagellae
whiplash - posterior and smooth
tinsel - anterior and ‘hairy’ - has many fine lateral mastigonemes.
some species have one of each - others one or the other.

6. Nutrition Fungi are heterotrophs
Produce extracellular enzymes which digest’ the food - then they reabsorb the products
Capable of producing a wide variety of these enzymes - can break down very tough, complex materials - lignin (wood)
keratin (hair, skin, nails)
suberin (cork)
melanin (black pigments)
chitin ( arthropod exoskeleton, other fungi)
cellulose (plants)
- hence major role as decomposers.

7. Nutrition Can grow on:-
1. Non-living substrates ( dead animals, plants, foodstuffs, paper, manure, etc (Saprobes)
2. Living organisms (Parasites, parasitoids or predators)

8. Nutrition. Some fungi live in symbiotic relationships
endophytes - live within plants without visible effect
mycorrhizae - associate with plant roots to mutual benefit
lichens - intimate association of alga and fungus as integrated organism

9. Nutrition/physiology:
Can live in high acid (pH 1) or alkaline (pH 9) environ.
tolerate cold or heat ( -5 to 60 C) or low O2
tolerate low water availability (.65 vs plants 0.98)
Most strains can make many compounds directly from simple or complex sources (source of C, N, inorganic ions = prototrophs
Some strains/mutants have lost ability to make a growth factor (eg vit. B1) = auxotrophic - so need this factor as a food source

10. Filamentous fungi hyphae may be aseptate (no cross-walls) - so form
multinuclear coenocytes - in this
case hyphae often wide and
fast growing - easily damaged.
or hyphae may be septate
Here hyphae usually narrower
sometimes with special mechanisms
to control nuclear content - tough

11. Filamentous fungi
hyphae can form many kinds of specialized structures:
infection pegs, haustoria
asexual and sexual spore-bearing structures
‘rooting’ structures - rhizoids and rhizomorphs
overwintering structures e.g. dark hyphal masses called sclerotia or thick walled spores

12. Cell structure Chitins + proteins proteins
Neurospora
Chitins + proteins proteins
glucan + protein
glucans
Walls - one to several layered, complex, contain:-
chitins (Eumycota)
cellulose (Chromista),
B-glucans (yeasts);
proteins including fimbriae.

13. Structure of a yeast cell wall

14. Cell structure Chitins + proteins proteins
Neurospora
Chitins + proteins proteins
glucan + protein
glucans
Walls - one to several layered, complex, contain:-
chitins (Eumycota)
cellulose (Chromista),
B-glucans (yeasts);
proteins including fimbriae.

15. Reproduction Life-cycle of most Eumycota Haploid Hyphae meiosis
mitosis
Vast number of asexual spores
Haploid Hyphae
Male and female organs
HAPLOID
Diploid spores - often adapted for overwintering/ survival
DIPLOID

16. Reproduction Life-cycle of some Chromista (Oomycetes Diploid Hyphae
mitosis
Vast number of diploid asexual spores
mitosis
Diploid Hyphae
Diploid spores - often adapted for overwintering/ survival
Male and female organs
DIPLOID
meiosis
Haploid nuclei
HAPLOID

17. Asexual stages = anamorph Sexual stages = teleomorph
Reproduction
Asexual stages = anamorph
Sexual stages = teleomorph
Together they make the holomorph.
Many species have both stages, each with specialized spores
In others only the anamorph known = ‘Deuteromycetes’.
Often difficult to correlate a known anamorph with a known teleomorph. Are they the same species?

18. Anamorphic Stages Vast numbers of spores can be produced:-
Bracket fungus can release 30,000,000,000 spores/day or over 4,500,000,000,000 /yr.
One wheat grain infected with stinking smut contains 12,000,000 spores
one 2.5cm colony of Penicillium can produce 400,000,000 spores
Air we breathe contains 10,000 spores/m3
often a cause of allergies, sick building syndrome and farmer’s lung

19. Teleomorphic stages fungi can be
homothallic - sex. reprod. can begin on a single strain (thallus)
heterothallic - two genetically different strains must come together for sexual reproduction
in heterothallic strains, mating-types determine sexual compatibility.
some species are hermaphrodite, some dioecious

20. Teleomorphic stages
In some fungi, unspecialized cells fuse to begin sexual reproduction
antheridium oogonium
In others specialized gametangia produced - either identical in both sexes, or specialized male (antheridia) and female (oogonia) organs

21. Teleomorphic stages sexual reproduction involves:-
plasmogamy - cell fusion between haploids
- via conjugation, anastomosis of hyphae or fusion of gametangia
karyogamy - nuclear fusion to make a diploid
meiosis - producing 4 (usually) haploid nuclei
(may later form 8 or 16 nuclei by mitosis )
spore formation - packaging nuclei into spores

22. Heterokaryons and Dikaryons
After plasmogamy, in some groups there is a long gap before karyogamy
Heterokaryons contain mixtures of genetically different nuclei
Dikaryons - each cell contains 2 nuclei - one of each genetic type
Homokaryons - cells with nuclei all of same type.
Heterokaryon compatibility genes determine ability of different homokaryotic hyphae to anastomose and form heterokaryons

23. Follow-up to lecture
Read text (Preface, Learn about fungi? Who me? ; and Chap 1).
Review today’s lecture slides on Bio318b Web page
Review terms used in this lecture (see text glossary)