OD and IPTG concentration

S.Ballal ballal_sv at hotmail.com
Sat Dec 22 19:23:51 EST 2001

Sorry Dominic,

I also disagree with you on this is much as Duncan does. 

Dominic-Luc Webb molmed <domweb at mbox.ki.se> wrote in message news:<Pine.GSO.4.43.0112211529240.20977-100000 at mbox.ki.se>...
> On Thu, 20 Dec 2001, Duncan Clark wrote:
>    > >In most of the places varying concentration of IPTG has been suggeste
>  d
>    > >for induction depending upon the expression system and other things.
>    > >Most of these are for an low ODs like 0.5-1.
>    > >
>    > >In case we need to work on high ODs like 50-100 or 150 would one
> You will never get that far for the simple reason that
> spectrophotometers peak out at about 3. They will give
> values up to about 4, which are meaninglessly beyond
> the linear range of the spectrophotometer. OD600 are
> absorbance values. Your bugs will already be dying
> at about OD600 of about 0.7.

Reaching higher OD's with E.coli is neither difficult  nor novel any
more. People have reached dry weights  of 100 g/ L ( that will make
the OD to be close to 250).  In a simple fermenter with pH and oxygen
control  one can reach
reach an OD of 20-40 very easily ( in less than 24 hrs).  Even in
shake flasks they can reach OD of 15 or so over 48 hrs !  Here we are
talking about plain old BL 21 strain

>    > >require much higher concentration of IPTG and if in what range is
>    > >generally used for such cultures.
> No. This will be useless. There will be so much antibiotic
> resistance in the medium that you can clear out nearly 100%
> of the antibiotic within minutes! Your soup could quickly
> be overrun by bugs spitting out these lethal concentrations
> of IPTG. They are quite good at beating this induction
> system if given need and opportunity. You give both need
> and opportunity with this protocol.

Quite true if you are using B-lactam based antibiotics. Though I am
not sure how significant role does it play in actual fermentation. 
There are still lot's of guys using B-lactam with out any major hitch
>    > I've always used the same concentration regardless of OD.
> This ends up making sense, but it was not very intuitive to
> me at first. I think 100 ?M is quite enough for most
> systems. I have several different T7 expression bugs. All
> of the working ones are killed by only 100 ?M IPTG. In fact,
> if your bugs still grow well in 1 mM IPTG, your system is
> not optimal. Consider a different bug, or subculturing.

Well some researchers use upto 2mM to induce. I have read one
reference where ~55 mM of IPTG !!! ( yes milli molar) was used to
induce a high cell density fermentation ( done by Covance biotech)

>    > The more critical bit is stage of growth rather than OD itself i.e.
>    > culture must be in logarithmic growth and not late log or stationary.
> I think I would agree, from my own experience. In general, it is
> better to have lower OD, below 0.5. Even at 0.5, ampicillin can
> be consumed within minutes in a typical T7 system, like BL21(DE3)
> and HMS174(DE3) lysogens and proper preparations of these
> are pretty much completely killed by 100 to 500 ?M IPTG. My
> best bugs, are totally killed by this treatment, with no
> growth whatsoever if suspensions with this treatment are seeded
> onto plates.
> Cheers,
> Dominic
> North 59 37' 30"
> East  17 48' 10"

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