chapter 24: fungi - BIOL 2130

fossil record

• little fossil evidence because of their soft, decomposable bodies, seemed to appear around 1 bya

• evidence of fungal hyphae remain in ancient plants — likely evolved from eukaryotes

• biochemical evidence (DNA and protein) of evolution among fungi and other eukaryotes

prototaxies

• one of the largest organisms on land during its time

• presence of this organism suggests unique lineage of multicellular terrestrial eukaryotes

• doubts about fungal status!

kingdom fungi

distinct kingdom of organisms in mid 20th century, crucial characteristic was its method of obtaining nutrients

• classified as part of the plantae kingdom until later in the 20th century

• organized by morphology of sexual organs, presence of septa (cross-walls in hyphae), and degree of chromosome repetition (ploidy)

like animals

• heterotrophic: derive energy from organic compounds

• cell walls composed of chitin for stability (like exoskeleton of arthopods)

• produce pigments (including melanin for UV protection and oxidation)

• store carbs as glycogen

like bacteria

• can absorb nutrients from environment across the cell surface

  • fungi via hyphae, bacteria via cell membrane

• can act as decomposers (break down organic matter and recycle nutrients)

structure

complain a complex structure like other eukaryotic cells, but NO chloroplasts

• color is a product of other cellular pigments, and cannot photosynthesize

• membrane bound nucleus: DNA

• DNA wrapped around histones like other eukaryotes

• mitochondria for energy

• other membrane bound organelles (ER, golgi, etc)

• thick cell walls like plants (rigidity and protection like plants)

anatomy

• mycelium

• reproductive structure

• spores

mycelium

network of hyphae that obtains nutrients, produces fruiting body, and is mostly underground

• through absorption (enzymes break down and digest)

• fruiting body: visible reproductive structure (ex: mushroom)

spores

involved in fungal reproduction, produced in the fruiting body, and haploid

• germinate when they hit damp soil (grow into new mycelium)

• single set of chromosomes

reproduction

can undergo both asexual and sexual

• most produce haploid spores → go thru mitosis → forms multicellular haploid organisms

• spores transported from parent via wind/animal leading to genetic variation

asexual reproduction

reproduction where spores form by mitosis and grow into multicellular haploid organisms, quickly making more fungi

• budding: expanded cytokinesis, bulge forms, nucleus divides via mitosis, new cell pinches off

  • ex: yeast

• fragmentation: hyphae break → each piece grows into new colony

• producing spores genetically identical to parent

sexual reproduction

reproduction that introduces genetic variation, typically rises from adverse environmental conditions

• when conditions threaten survival

• two mating types produced 

• homothallic: self fertile

• heterothallic mycelia: require two different but compatible mycelia

• compatible haploid hyphae fuse → diploid nucleus → meiosis → haploid spores with new DNA → germinate → new mycelium

nutrition

fungi are heterotrophic and digest before ingesting

• hyphae secretes exoenzymes, take in and break down large organic molecules for energy

• mycelium causes smaller molecules to be absorbed across cell membrane

• saprobes: most fungi obtain nutrients from decaying organic material

• some are parasitic: derive nutrients from host tissue, sometimes causing disease (ex: athletes foot)

forms

adapt their cellular form to optimize survival in temperature, humidity, nutrients, reproduction, host interactions, etc.

1) unicellular: grow by budding or binary fission (ex: yeasts)

2) multicellular: grow as hyphae and form the mycelium to produce fruiting bodies (ex: mushrooms, molds)

3) dimorphous: do both when triggered by environment

• ex: honey mushroom — small in size, grow big amounts underground and can have a hidden growth form with small visible reproductive form

• ex: amanita muscaria — pigments in cell wall protect against UV and predation

habitat

• moist, slightly acidic

• both dark and light environment (mostly dark since most are underground)

• vary in oxygen requirements

  • most obligate aerobes: need oxygen

  • some obligate anaerobes: oxygen kills them

• have ability to live almost anywhere (from soil and decaying matter to living hosts!)

decomposers

break down organic material to release molecules necessary for life to exist

• nitrogen and phosphorus!!

• would remain trapped in decaying material if not for them!

• this happens due to digestion before ingestion

mutualistic relationships

• mycorrhizae (plant/fungi)

• lichen

• animal

mycorrhizae

mutualistic relationship between plant roots and fungi

• 90% of plant species

• ecto (outside): wrap roots in sheath of hyphae

• endo (inside): fungi grows within roots

• endophytes: fungi live in plant, secrete toxins to prevent predation and resist env stress

• most terrestrial plant roots (on land) connect with fungi

• exchange of nutrients and water to benefit both!

lichen

mutualistic relationship between photosynthetic organism and fungi

• ex: algae, cyanobacteria

• neither organism can live outside this relationship

• sensitive to air pollution

• good indicator species!

animal

mutualistic relationship between animal and fungi

• animals can provide food, protection, or dispersal for the fungus 

• fungi can provide nutrient or food for the animal

• ex: leaf cutter ants get leaves, protect it from parasites, release spores on them, and fungi grow for food!

• fungivores: animals eat fungal spores, unknowingly dispersing to their diet

  • ex: truffle-eating pigs

human benefit

• nutrient cycling in ecosystems (nitrogen, phosphorus, etc.)

• pest control

• mycorrhizae to plant growth and agricultural goals

• consume food: mushrooms, cheese, alcohol, bread

• medication

• pulp paper textile industry, food industry, beverage, biofuel, biocatalysts, env management, animal feed, household items