Lecture 9 -Metabolic engineering of bacteria Flashcards Preview

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What are the empirical approaches to improving yield?

can improve yeild of microbial processes through random mutation and seletion to give improvement, not directed


Give an example of the empiricle approaches to improving yield

yeild of penecillin from inital experiments 10 ug/l through mutation and seletion of strains led to greater yields 10g/l


Two approaches to improving yield



What is rationale design to improve yield?

being able to work out how to improve yield of certain cell processes by understanding all the processes it can do and how they are controlled


What do we know about E.coli and why is it a model bacterium?

-biochemical and genetic information for 500+ enxymes
-2000 proteins have known functions
-37C aerobic growth
-grow in simple defined medium doubling hourly
-high biosynthetic capability
-high metabolic capacity
-can use anaerobic respiration, aerobic respiration or fermentation


What is metabolic flux?

rate of turnover of molecules through a metabolic pathway, regulated by enzymes in a pathway


What 5 ways are there to increase flux through a particular metabolic pathway?

1- removal of rate limiting transcriptional and allosteric control
2-kinetic enhancement of rate limiting step
3-genetic blockage of competing pathways
4- enhanced carbon commitment to primary metabolic pathway from central metabolism
5-enhanced transport of substrate into cell


How can metabolism be directed for increased protein production?

In TCA cycle, protein synthesis becomes limited by amino acid supply.
-10 amino acids are derived from TCA cycle metabolites
Can INCREASE FLUX of carbon to amino acid biosynthesis by reducing wasted flux to acetate
-delete enzymes that make acetate
-add enzymes add more C to TCA cycle
-can delete genes for catabolic enzymes keep amino acid pool high


What is phenylalanine prododuction in E.coli used for? And problems with production pathway?

-making sweeteners
-one of 3 aromatic amino acids synthesised in E.coli, some parts pathway shared
-cell tightly regulates expression and activity of enzymes in pathway depending on level of products in the cell


How can phenylalanine expression be increased in E.coli?

1) remove feedback inhibition
-use phenylalanine analogoue that will always repress so that the cell mutates enzyme not to respond
2)Overexpress similar enzyme not inhibited by phenylalanine
-use promotor not regulated by tryptophan
3)Remove competing pathways
-delele genes for tyrosine and tryptophan syntheisis
4)Enhance carbon commitment to primary metabolic pathway from central metabolism
-increased supply of E4P and PEP precursors


How is indigo produced in E.coli?

1)napthalene dioxygenase from pseudomonas ezpressed in E.coli and E.coli grown in presence of tryptophan
2)E.coli expresses a catabolic tryptophase which makes indole as product
3)indole converted to indoxyl by napthalene dioxygenase
4)undergoes spontaneous oxidation to indigo


What is a problem with indigo production in E.coli?

Indoxyl also oxidised to isatin which forms completely different dye (deep burgandy) -> as this is a competing spontaneous pathway cannot be deleted genetically


What is indigo used for?

important for cotton and blue jeans
produced originally from sea snails


What is Sinorhizobium meliloti (RMBPC-2)?

an engineered microbe approved in USA for agricultural use


What dose Sinorhizobium meliloti do?

-forms a symbiotic relationship with legumus plants to fix nitrogen, modified bacteria can fix nitrogen at a greater rate
1-infects roots of allella plant and form roto nodules
2-differentiates into form that can fix N2 from air and convert to NH3
3-incorperated into plant biomass


What genes have been overexpressed in Sinorhizobium meliloti strain RMBPC-2?

1)Increased expression of DctA
-DctA encodes a membrane transport protein for dicarboxylates are the preferred C source for bacterium in nodule -> increases rate of metabolism in nodule and amount of N fixed
2)Increased expression of NifA
-NifA transcription factor activates gene required for nitrogen fixation leading to more copies of the protein and more nitrogen fixation


Positives and negatives of overexpression of DctA and NifA in Sinorhizobium meliloti strain RMBPC-2?

Increased yield by 10%
Carry antibiotic resistance genes



around 0.5 billion


Where is the malaria treatment Artemisinin obtained from?

from plant Artemisia annua


Features of arteminisin

Malaria treatment
Sesquiterpene lactone endoperoxide
machanism of action unknown
can be made synthetically but very expensive


What is arteminisin synthesised from in plants?

FPP (multiple uses in the cell)


How have microbes be engineered to make artemisinic acid

engineer S.cerevisae to make the precursor to artemisinic acid FPP through metabolic engineering


1-How can yeast be engineered to make more FPP?

1) Mutate the transcription factor that normally controls the synthesis of pathway, to be constituatively active. Increases synthesis of some enzymes
2) Alter genes that encode tHMGR and ERG20 to be under the control of a galactose inducible promotor
3)Add extra copies of tHMGR gene on the chromosome


What does FPP stand for?

farnesyh pyrophosphate


2-How did engineer yeast to make more FPP available to make malaria drug?

1) manipulated erg9 gene so expression was repressed by methionine in growth medium
-reducing expression of erg9 decreases amount of enzyme present and flux of reaction, cannot remove completely as needs flux though pathway to make sterols


3-How did scientists use the identification of genes in plant that catalysed the steps between FPP and artenisimic acid to increase yield?

1)cloned and manipulated gene encoding ADS reaction so expression was induced in presence of galactose
2)manipulated new genes isolated from plant so that their expression was induced with presence of galactose


What were the three ways FPP production to arteminisic acid was increased in yeast cells?

1-Engineered yeast to produce moreFPP
2- Enginnered so that more FPP was available for making drug
3-Identified genes that catalysed the steps between artenisimic acid and manipulated them


After genetic enginnering in yeast cells to produce FPP and arteminisic acid, how were yeast cells grown?

-grown in presence of galactose and methionine


What are the main principles of genetic engineering to increase yield shown by the arteminisic acid production?

1)Increase flux through producing pathway
-Increase gene dosage, add more copies of key genes
-Upregulation of expression of genes in the pathway
2)Repressed flux of reactions that compete for desired precursor
-downregulate the expression of competing pathways
3)Express recombinant proteins to enable use of an endogenous precursor to synthesise novel metabolites
-Identified genes that were responsible in plant and managed to express in yeast