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

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

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

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

Some fungi (Chromista + Chytrids) have motile forms (possess flagellae) Flagellae have typical 9 + 2 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.

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.

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

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

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

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

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

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.

Structure of a yeast cell wall

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.

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

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

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?

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

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

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

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

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

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)