Hi all,
can anyone explain me why for some procedures it is better to use bacteria in log-phase and for other ones bacteria in stationary phase? For example for DNA and plasmid purification you want an overnight stationary phase culture, while for stuff like transformation you want a log phase culture..
Thanks
Dear Silvia, the main reason why some experiments are performed in log or stationary phases is gene expression.
Bacteria have really complex regulation pathways that will depend on the growth medium that you use, the temperature and the growth phase in which bacteria will be. Each of this parameters will have an effect on gene expression and thus in the final product (as Teresita and Becky have written) some proteins are only produced in stationary phase because specific signaling pathways are activated, this is usually under the control of quorum sensing (a type of bacterial communication) which depends on the density of bacterial population.
For plasmid extraction you use a night culture to increase the yield of the plasmid extracted, the more bacteria you have the more plasmid will be extracted. For bacterial transformation the fact of using log phase bacteria is the idea of fitness, your bacteria are constantly in division at this phase so when you transform at this point you increase the probability that the bacterium transformed will divide rapidly.
Dear Silvia your question has many answers it all depends on what are you looking for. Ex. if you want to isolate a protein that it is only produced when cultures are in stationary phase like most secondary metabolites you should wait until the culture has reached this stage. On the other hand if you are looking for proteins for house keeping it will be a better idea to use in log-phase for example. DNA you can have it at any point of cultivation but RNA depends on the stage of growing to asure it will be present.
Dear Silvia, as Teresita puts it, it will depend very much on what you are looking for in the cultures. For example if you are working with antibiotics, enterotoxins,and endospores you will need to work with cells in the stationary phase becasue this is when the secondary metabolites are produced. If you are targeting primary metabolites like nucleotides, aminom acids,organic acids and enzymes, you will need to work with cells in the trophophase or exponential phase of growth
Dear Silvia, the main reason why some experiments are performed in log or stationary phases is gene expression.
Bacteria have really complex regulation pathways that will depend on the growth medium that you use, the temperature and the growth phase in which bacteria will be. Each of this parameters will have an effect on gene expression and thus in the final product (as Teresita and Becky have written) some proteins are only produced in stationary phase because specific signaling pathways are activated, this is usually under the control of quorum sensing (a type of bacterial communication) which depends on the density of bacterial population.
For plasmid extraction you use a night culture to increase the yield of the plasmid extracted, the more bacteria you have the more plasmid will be extracted. For bacterial transformation the fact of using log phase bacteria is the idea of fitness, your bacteria are constantly in division at this phase so when you transform at this point you increase the probability that the bacterium transformed will divide rapidly.
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