Normally we will start induce our protein after an OD of the bacteria reaches 0.6 to 0.8. What will be happened to our protein if we induce after the bacterial OD about 2 at 600 nm?
After passing the log phase, major metabolic changes follow in cells as bacteria try to adapt to an environment (stationary phase) where nutrients (oxygen, carbon source) are depleting, wastes are building up and neighbor density becomes prohibitory for growth.
Initially, some oxidative stress is expected to rise, but eventually cells cope with this by shifting its gene expression machinery to detoxicification and antioxidation. The cells are also trying to spend more energy on repairing wears and tears (lipid, DNA, proteins), rather than "seriously" expressing good proteins of nice folding.
Even the lipid profiles of log phase, stationary phase, and death phase are expected to differ, not to mention protein / mRNA / metabolomic profiles.
Therefore, it is not a good idea to induce protein expression in a stagnant pool of crowded bacteria.
0.6 to 0.8 is the OD when bacteria is in exponantial phase of the growth.
If you induce very late you will not get a good concentration of your recombinant protein. On the other hand if you induce very early, due to high concentration of recombinant protein bacteria might turn into inclusion body.
After passing the log phase, major metabolic changes follow in cells as bacteria try to adapt to an environment (stationary phase) where nutrients (oxygen, carbon source) are depleting, wastes are building up and neighbor density becomes prohibitory for growth.
Initially, some oxidative stress is expected to rise, but eventually cells cope with this by shifting its gene expression machinery to detoxicification and antioxidation. The cells are also trying to spend more energy on repairing wears and tears (lipid, DNA, proteins), rather than "seriously" expressing good proteins of nice folding.
Even the lipid profiles of log phase, stationary phase, and death phase are expected to differ, not to mention protein / mRNA / metabolomic profiles.
Therefore, it is not a good idea to induce protein expression in a stagnant pool of crowded bacteria.
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