We often induce protein expression when OD600 of E. coli culture reaches 0.4-0.8. What is/are the effect(s) of the pre-induction OD600 on expression level and stability of target proteins from bacteria? What will happen if we induce target protein expression at low and high pre-induction OD600?
Protein expression is a metabolic burden for the bacterium. Furthermore, the final protein concentration often correlates with biomass. If you induce very early, you cultivate your bacteria throughout the whole process with this metabolic burden of protein expression which leads to reduced growth rates and finally to a lower OD600 and consequently lower protein concentration after a given time. Your process is less efficient. If you induce late, there is less substrate left in the medium as the bacteria used this for their growth and survival. So this substrate is missing to produce the protein. This could lead to reduced protein yields as well. The ideal OD600 to induce protein expression varies with the medium and your protein of interest: if you , e.g., have a rich medium (such as TB), an induction at higher OD600s might not be disadvantageous while it is required for some toxic proteins.
Protein expression is a metabolic burden for the bacterium. Furthermore, the final protein concentration often correlates with biomass. If you induce very early, you cultivate your bacteria throughout the whole process with this metabolic burden of protein expression which leads to reduced growth rates and finally to a lower OD600 and consequently lower protein concentration after a given time. Your process is less efficient. If you induce late, there is less substrate left in the medium as the bacteria used this for their growth and survival. So this substrate is missing to produce the protein. This could lead to reduced protein yields as well. The ideal OD600 to induce protein expression varies with the medium and your protein of interest: if you , e.g., have a rich medium (such as TB), an induction at higher OD600s might not be disadvantageous while it is required for some toxic proteins.
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