Naked Science Forum

Life Sciences => Cells, Microbes & Viruses => Topic started by: toan on 12/07/2007 02:24:58

Title: Why should the optical density of my bacterial cultures suddenly drop?
Post by: toan on 12/07/2007 02:24:58

      I incubated a Ecoli medium at 37oC. The optical density increased up to 1.4, and it started going down. Something killed my bacteria? This has happened for many times? Does anyone know the reason? Thank you very much

Title: Re: Why should the optical density of my bacterial cultures suddenly drop?
Post by: Robinson on 05/09/2007 23:20:33

That's pretty hot... but it could be density issues - too many of them killed each other. Or it could be that they used up their growing medium, or they got their own virus (seems unlikely).

Title: Re: Why should the optical density of my bacterial cultures suddenly drop?
Post by: WylieE on 06/09/2007 07:39:55

Hey Toan,
 Seems pretty unlikely that your optical density would go down, even if they were dead. . . .the cells would still be in there unless they are getting lysed.  Or maybe I am just not understanding what you mean.   Maybe it has something to do with how you are measuring your samples, how you are diluting your sample before you measure, are you mixing the sample well? Reblanking your spec?

 You might check out this site for advice:
http://molecularbiology.forums.biotechniques.com/forums/index.php

Good luck!
Colleen

Title: Re: Why should the optical density of my bacterial cultures suddenly drop?
Post by: WylieE on 06/09/2007 07:55:00

Another couple thoughts. . .
Depending on your measurement technique when cultures become too dense the measurement is no longer accurate so you have to do a dilution and calculate back.  I usually start doing dilutions when the OD hits 1.
Maybe you are actually past 1.4 and just not able to measure it accurately and your cells are lysing from overcrowding.