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During some cultivation experiments for my bachelor thesis I noticed that in liquid culture my bacteria (E. coli) grew differently, according to the position in the shaking incubator.

Because the goal was just to induce protein expression at a given OD, I altered the position of the flasks in the shaker, so the cultures were at a similar OD and I could add the IPTG to all of them at the same time.

Now I wonder if someone else noticed this phenomenon (Literature to cite would be great, I couldn't find anything until now) or if I did something wrong. Maybe it's also known and ignored for longer times? The cultures more in the back of the incubator grew faster, so I think it's because of temperature alterations when opening the incubator to draw samples for growth kinetics, but I'm not sure about this at the moment.

Thank you for helping me :-)

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  • $\begingroup$ Is it possible, that there are different amounts of shear stress involved in different flasks? Cells can die due to shear stress, and E. coli is possibly more sensitive to shear stress than a gram positive bacteria. $\endgroup$ – inf3rno Nov 1 '14 at 14:31
  • $\begingroup$ No offense, but how reliably are your OD measurements? I noticed that there can be some difference, depending on where in the fask you take a sample. Also when you stop the incubator to take samples, cells start to sediment. This can influence the measurement for the later flasks from which you took samples. $\endgroup$ – Chris Nov 1 '14 at 19:30

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