fungal biotechnology Flashcards
Sir Alexander Fleming
o In 1928, working with staphylococci (a bacterium that can cause sepsis)
o Noticed clear zones with no bacterial growth around a mould growing on the plate
o Discovered moult was effective against bacteria causing scarlet fever, meningitis, diptheria
o Published results but was largely ignored
Sir Alexander Fleming
o In 1928, working with staphylococci (a bacterium that can cause sepsis)
o Noticed clear zones with no bacterial growth around a mould growing on the plate
o Discovered moult was effective against bacteria causing scarlet fever, meningitis, diphtheria
o Published results but was largely ignored
Howard Florey & Sir Ernst Boris Chain
o Running a research programme on antibacterial substances
o In 1939, used penicillin culture in mice following reading Fleming’s paper
o Showed it had both antibacterial properties and lack of mammalian toxicity
o Norman Heatley (recruited by Florey) devised methods for mass culture in bed pans, assay, and extraction using solvents
Early use of penicillin
Albert Alexander
▪ Sratched by rose thorn
▪ Got sepsis, caused by pathogenic bacteria
▪ Abscesses over head and shoulders, eye infected and removed, lungs infected. Near death.
▪ Given penicillin, fever broke within a day
▪ Not enough penicillin to continue treatment (despite best efforts – extraction from urine!!). Died.
▪ Still showed value of penicillin
WW2
▪ Death rates from infection near 0, contrast to 15% in WW1
▪ Government subsidised factories willing to make penicillin for war effort
Later developments with penicillin
Drug development & Gene research
▪ Transition from using bed pans to fermenters
▪ Unusually for eukaryotic genes, found clustered together – more similar to bacterial operon!
▪ Genes from different penicillin species have v high homology
▪ Also high homology to to β-lactam antibiotics produced by Streptomycetes bacteria
→ suggesting common ancestry and bacterial to fungal lateral gene transfer ~370mya
▪ Modern drug development based mainly on duplication of gene clusters, causing ~15,000x increase in yield per g of culture in 70yrs. Colocalisation means they are easy to replicate.
How to antibiotics work?
• There are multiple targeted sites of action in bacteria
o Penicillin targets bacterial cell wall
o Inhibition of 30S/50S bacterial ribosomal subunits, interfering in protein synthesis
- Ribosomes are different to ours so can be targeted :)
o Cytoplasmic membrane structure
Why do antibiotics stop working?
Bacteria have their own mechanisms to become immune to antibiotic o Prevent drug uptake o Drug modification o Drug inactivation o Alteration of drug target
Antimicrobial resistance
o Naturally occurring isolates with resistance will occur
- Overuse of antibiotics selects for resistance
- Conjugation transfers plasmids at high frequency (lateral gene transfer)
- Many antibiotic resistance genes are plasmid encoded
Eg. MRSA (methicillin-resistant Staphlylococcus aureus)
o Increasingly pathogens are becoming resistant to multiple drugs
Eg. Multi-drug-resistant Mycobacterium tuberculosis (MDR-TB)
- We thought we could get rid of TB, now nearly untreatable
Solutions to antibiotic resistance
- give 2
- New antibiotics
o However, these take 10-25 yrs to develop, cost millions of dollars
o Not attractive to drug companies anymore due to the speed at which they become completely obsolete - Abstinence
o Only use when absolutely necessary
o Removes the selection pressure for resistant bacteria, bacteria lose plasmids
Characteristics of a fungus suitable for industrial use
▪ Able to grow and form product in large-scale culture
▪ Spores easily to inoculate and germinate in large fermenters
▪ Rapid growth to produce desired product
▪ Grows in inexpensive nutrient eg. Waste starch
▪ Not pathogenic
▪ Able to GM
Uses of fungi in industry
o Food
- Eating whole (mushrooms)
- Brewing, baking, cheese making
- Quorn mycoprotein
- For primary metabolites eg. Organic acids
o Useful products
- Antibiotics
- Alkaloids and gibberellins
- For secondary metabolites eg. Enzymes, β-lactam antibiotics
o As hosts for secretion eg. Of mammal proteins
o Bioremediation & waste treatment
o Biological control
We must be wary of alfatoxins (eg. Secondary metabolite produced by Aspergillus flavus)
Name 2 fungal species used in industry and what they’re used for
Aspergillus niger (ascomycete)
- Produces citric acid
- Used in food and drink flavouring (eg. jam)
- Fungus is deprived of iron, tricking it into producing excess citric acid as a siderophore to try and acquire iron from the environment in chelate form
Aspergillus niger (ascomycete)
Aspergillus niger (ascomycete)
- Produces citric acid
- Used in food and drink flavouring (eg. jam)
- Fungus is deprived of iron, tricking it into producing excess citric acid as a siderophore to try and acquire iron from the environment in chelate form
Puccina graminis
Basidiomycete
• Causes wheat stem rust
• Serious pathogen, causing up to 100% yield loss
• Has caused great historical famines
Two host plants
- Barberry leaf
- Wheat
Infection event – biotrophy in leaves
- When spore lands on suitable surface (eg. Barberry leaf)
- It germinates, forms germ tube that moves along leaf and forms appressorium that grows a pointed hyphae through the epidermis and between cells in the cortex
- This is done using turgor pressure in the infection peg. Sometimes enzymes are also employed
- Mycelium propagates in leaf mesophyll, some hyphae enter cells and form haustoria which absorb nutrients
Can plants resist fungal diseases?
How?
Localised apoptosis
• Localised, plant-induced cell death deprives biotrophic pathogen of food
• Often only a single cell dies, so no observable symptoms
• White spotting on leaves shows where appressorium formed and started to penetrate a plant cell, which underwent apoptosis! – hypersensitive response
