Gr- Strain Improvement

Front 1

how was penicillin yield increased for the first time

Back 1

Andrew Moyer substituted lactose for sucrose

a ten-fold increase in yield was achieved by adding corn-steep liquor to the fermentation

further increased by addition of penicillin precursors (phenylacetic acid)

Front 2

how were submerged cultures introduced

Back 2

molds grown in constantly agitated and aerated tanks.

Florey's strain did not produce significant penicillin in submerged cultures, new strains needed to be found

Front 3

which is the historical strain from which all modern strains come from?

Back 3

the canteloupe strain, found on a mouldy canteloupe from a Peoria fruit market

later increased by exposing to X-rays and UV radiation

Front 4

beta lactam ring is the key thing about penicillins

growth of fungi is less straight forward than bacteria
fungi grow on the surface of liquids, low density

mutation may target various processes:
- amount, activity, regulation, of enzyme
- transport out of the cell
benefits are multiplicative
combining mutations by series of mutagenesis procedures in a single cell we can get combinatorium benefits

current penicillin production is 20g/l
all done with by blindly introducing mutations

knowledge on biochemistry can provide insights in strain improvement

Back 4

c

Front 5

amino acid production

lysine are widely used as a food additive for animal foods

bacteria do not secrete aminoacids
biosynthetic repressors
eg. arg production is self regulated operon

Back 5

c

Front 6

several different aminoacids within the same pathway
(met-thre-iso-lys)

corynebacterium glutamicum
used commercially for aa production
asp: transferanceof amino group on TCA component. aa llinked to central metabolism

protein + genetic level of regulation
allosteric regulation is common in aa

enzyme that does not respond to allosteric regulation
knockout of enzyme directs all metabolites down a specific path, acquire mutant that's auxotrophic for three a.a (thr/met/iso). make mutations then screen. growth in presence, no growth in absence)

auxotrophic mutants essential for production
regulation mutants also very important, how to isolate though... inhibitors + genetics
aminoacid analogs inhibit enzyme by bining in the same way (alosteric regulation means binding on a different site) variations in structure

lysine analogue switches off aspartate kinase, switches off biosynthesis of lysine by 'tricking organism' that there is lysine present.

allosteric regulaio

Back 6

c

Front 7

mutants resistant to aa analogues have no regulation of aa production -> high levels of production

remove his degradation enzyme with other mutations resistance to different analogues, combinatorial

13g/l of Histidine in the medium

regulation can be overcome

Back 7

c

Front 8

how to acquireauxotrophic mutants

Back 8

the penicillin selection method.
- penicillin kills growing bactreria (inhibits petidoglycan synthesis)
- firstly grow cells in presence of arginine (relaxes selection for arginine production)
- then move to arginine free medium + penicillin
- cells that GROW (prototrophs) DIE
- selects for auxotrophs (arg-)

Front 9

why are auxotrophs useful

Back 9

regulations (feedback inhibition, repression, attenuation) require the end product in order to function. by blocking a step, no end product is made, leading to endless production of an intermediate, which often can be easily chemically converted to the end product, or is useful in itself (eg L-ornithine, medically relevant)

also useful for channeling intermediates of a branched pathway to only one of the branches, often increasing the production of that one. this also decreases the negative feedback effects of the other end products.

major drawback is that supplementary amino acids need to be added (the ones that cannot be synthesised)
- excess may downregulate production
- more expensive
auxotrophs not ideal for aa production

Front 10

why are regulatory mutants better

Back 10

-analogs may bind allosterically to the enzyme or the repressor of the enzyme's gene, in either case shutting off the synthesis of that amino acid.
- this halts the growth of the cell, due to deficiency in that aminoacid
- mutants lack feedback inhibition, constitutively producing the amino acid

Front 11

how do you acquire them

Back 11

-synthesize wide variety of analogs
- select for the analogs that inhibit growth of wild-type in minimal medium
- use those analogues to select for mutants that can GROW in their presence. those mutants are the desired regulatory mutants

** ineffective for multi-level regulation (eg many pathways in E. coli are regulated at three levels; fedback inhibition, repression and attenuation)
> that is because mutation is rare, co-occurance of two-three desirable mutations is very unlikely
> there are organisms with more simple regulation

Front 12

what other mutations may be beneficial for overexpression?

Back 12

-knock out enzymes which degrade amino acids in order to yield carbon. (eg proline oxidase in Serratia marcescens)

- osmoregulation mechanism: proline acts as an osmoprotectant solute.