I inserted 4 different genes in vector, and cloned in E.coli.
when I grow them on IPTG containing plate, Each bacteria grow different.
If I pick each bacteria with different number, then each plate will have different tendency.
but always same tendency.
even more interesting is that 4 proteins has same function but different activity.
The bacteria which have more active protein grow not well, but have less active protein grow very well on IPTG plate.
but that protein is not toxic to E.coli.
I wonder why this happened, so I looking for answer or papers.
Thanks for reading.
Just to make sure I'm understanding you correctly: You have four different genes which encode for proteins that have the same enzymatic function, but differing catalytic activity. When you plate them on media which induces expression, the higher the catalytic activity of the enzyme they're expressing, the smaller the colonies tend to be. Is that right?
Based on that, my assumptions would be:
A. The enzymatic activity interferes with a normal part of E. coli growth. Maybe it depletes a nutrient, produces a product which is toxic in high amounts, or something along those lines. Enzymes which are better at doing whatever that activity is would obviously be harder on the cell.
B. Protein flexibility can effect enzymatic activity, so it could be related to that. Maybe the more active enzymes are more labile and prone to exposing hydrophobic residues, which causes them to auto-aggregate when present at high concentrations, as an example.
Those two are not necessarily mutually exclusive and there's other possibilities, but those are the obvious explanations without me knowing a lot of specific details about your project. Also, keep in mind that others reporting protein toxicity in E. coli are probably doing so on an arbitrary scale as a qualitative judgement unless they're showing properly controlled growth curves. Artificially over expressing essentially any protein to the point where it takes up 1/3 of the cell's total protein content will not be great for normal growth.
It is not clear from your question whether you are referring to 4 proteins which differ in catalytic activity as Alexandra Johnson assumed, or if you are just talking about different levels of expression resulting in clones with higher or lower amounts of enzyme activity. Her answer is good for that assumption, but if you are only talking about protein amounts you may just be looking at metabolic load, if you make too much of a protein regardless of activity, it is imposing a metabolic load on the cell which could result in slower growth.
If you have different proteins with different enzymatic activities then the clone that makes the bacteria grow slower may be affecting a vital function of the bacteria, such as interfering with the function of an essential protein.
If the clones express the same protein at different levels then it is because of energy drainage due to metabolic load.
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