Fungal biotechnology and antifungals

• what is mycorrhizae

  plant-fungus mutualisms (all plants form mycorrhizae except Chaenopodiaceae)
• why do mycorrhizae form

  • fungal mycelia are extremely efficient at scavenging nitrogen and phosphorous which they swap with the host plant in exchange for a reliable carbon source
  • without them plants would grow much more slowly
• Arbuscular mycorrhizae

  • dominant type
  • produced by Glomerulomycota
  • vesicular-arbuscular mycorrhiza are dominant form
• Ectomycorrhizae

  • important in coniferous forests (Basidiomycota)
  • important as saprotrophs
  • important in mineral weathering
• Ericoid mycorrhizae

  • Associated with rhodedendrons
  • ericoid plants dominate in peat bogs, moorlands or heatherlands
  • characteristic low nutrient availability, low pH, high C:N ratio and heavy metal toxicity
  • enable plants to sustain these environmental stresses and successfully compete with other plants
• Orchidaceous mycorrhizae 

  • associated with orchids
  • belong to the basidiomycetes
  • infection is restricted to primary cortex
  • transport of carbon compounds from fungus to host-plant may be realised by two ways
  • through the plasma membrane of living pelotons (in trophocytic phase)
  • by phagocytosis of collapsed fungal endophytes (in phagocytic phase)
• Monotropoid mycorrhizae 

  • associated with achlorophyllous plants
  • mycorrhizae connect together different plants in a forest
  • 32P migrates to adjacent trees
• process of leaf litter decomposition

  1. freshly fallen needles decompose slowly over a 7 year period
  2. fungi of several genera aid in successive decomposition of needles
  3. degradation products from one group of fungi create the conditions for growth of the next group in the succession
• wood decay

  • wood made from secondary cell walls is the most widespread substrate on the earth
  • wood is composed mostly of cellulose which is a polymer of sugars and lignin
  • bacteria and fungi are responsible for the decomposition of cellulose
  • the ability to degrade lignin is restricted to fungi (mostly basidiomycota and a few ascomycota)
• what is cellulose

  an unbranched polymer of beta 1,4 linked glucose 
• how much cellulose is synthesised each year

  10^11 tonnes
• what do endoglucanase do

  attacks cellulose at random, producing glucose, cellobiose (a disaccharide made up of two glucose molecules) and some cellotriose (a trisaccharide)
• what do exoglucanase do

  attacks from the non-reducing end of the cellulose molecule, removing glucose units, it may also produce cellobiose
• what does cellobiase do

  responsible for hydrolysing cellobiose to glucose
• what does lignin decomposition depend on

  lignin breakdown depends on oxidation mediated by fungal enzymes that produce ROS
• what does lignin peroxidase do

  catalyses H2O2 dependent oxidation of lignin (haem containing protein)
• what does manganese peroxidase do

  catalyses H2O2 dependent oxidation of lignin 
• what does laccase do

  catalyses demethylation of lignin components (copper containing protein)
• what rot does cellulose and lignin breakdown produce

  white rot
• how does white rot affect wood

  leave the wood bleached and with a stringy consistency
• what are potential uses with white rot

  bioremediation and biopulping (reduction of wood fibres in paper production)
• what does cellulose breakdown produce

  brown rot
• how does brown rot affect wood

  has a crumbly consistency, breaking up into cubucal fragments and has a red brown colour
• matsutake

  • can sell for $200 a piece in tokyo markets
  • overall value of harvest is £2-4 billion annually
• white piedmont truffle

  • white piedmont truffle sells for £2000-4500 per Kg
  • record was £165000 for a 1.5 kg specimen
• cepes

  used in heinz mushroom soup 
• Quorn - mycoprotein

  • Fusarium venenatum
  • quorn is 12% protein and contains all the essential amino acids for adults
  • mycoprotein is high in dietary fibre
  • mycoprotein is low in fat and saturated fats and contains no cholesterol or trans fats
  • low in sodium
• what does fermentation do

  converts materials into products that are

  • more readily digested
  • enriched in nutritional qualities
  • flavour enhanced
  • altered in physical form or texture
  • preserved
• what are antifungals site of action

  cell wall or DNA/RNA synthesis or the cytoskeleton
• what are polyenes derived from

  Streptomyces bacteria in 1950s
• how do polyenes work

  • previously thought to bind to ergosterol in the fungal cell membrane and thus weakening it and causing leakage of K+ and Na+ ions
  • now thought to bind and extract ergosterol directly from the cellular membrane thus disrupting the cellular functions ergosterols perform
• examples of polyenes

  amphotericin B and nystatin
• how do azoles work

  inhibit conversion of lanosterol to ergosterol by inhibition of lanosterol 14alpha-demethylase
• examples of azaleas

  • imidazoles - ketoconazole, miconazole
  • triazoles - itraconazole, fluconazole, voriconazole, posaconazole, isavuconazole
  • Thiazoles - abafungin (discontinued)
• examples of allyamines

  terbinafine, naftifine and thiocarbamate tolnaftate
• mechanism of allylamines

  competitive inhibition of squalene epoxidase blocking conversion of squalene to lanosterol
• mechanism of echinocandins

  inhibit the synthesis of beta-glucan in the fungal cell wall via noncompetitive inhibition of the enzyme 1-3-beta glucan synthase
• examples of echinocandins

  caspofungin, micafungin, anidulafungin
• mechanisms of flucytosine

  • two major mechanisms
  • converted into the cytostatic fluorouracil which interferes with RNA synthesis this blocking protein biosynthesis
  • undergoes conversion to 5-fluorodeoxyuridine monophosphate which inhibits fungal DNA synthesis
• azole resistance

  • primarily due to increased efflux of the drug from the fungal cell
  • resistance also arises from modification of the sterol biosynthesis pathway
  • caused by point mutations and promoter insertions in CYP51A in A. fumigatus
  • in other fungal species such as C. neoformans, over expression of the drug target and efflux pumps caused by chromosomal aneuploidy and hypermutation is common