Semicontinuous culture

Dennis Bayrock dbayrock at sk.sympatico.ca
Fri Aug 28 00:03:45 EST 1998

>Your collegues are correct in regards to fed-batch
>> fermentations- fresh medium is added (at a constant rate or step-rate
>> increased) until the working volume is reached (at which point the
>> fermentation becomes a continuous culture). There are also variations on
>> classical cascade fermentation where fresh medium is added as in fed
>> the fermentation is then called a fed-batch cascade fermentation.
>>     I hope this information helps!

>Different laboratories (and industrial plants) use different terms.
>What Yarlipo described is a process we freqently use, and call
>"semi-continuous", sometimes with "intermittent feed" attached.  What
>we call "fed batch" is simply one cycle of this, with a final harvest
>of broth when the full volume is reached.  What you describe is what
>we call a fed-batch beginning to a chemostat run.  Continuous cultures
>are divided into chemostats (which have continuous media fed in and
>harvest drawn off), and perfusion runs (which include cell retention
>or cell recycle).
>     I don't think there is much agreement on vocabulary between
>different institutions.  I've worked for 4 biotech companies as a
>fermentation specialist, and they've all had different terms.


    I agree Owl that there needs to be a standard set of definitions for the
various modes of fermentation. I've been doing fermentations in my academic
career for 10 years and each time I see a continuous culture or fed-batch
culture in the journals or in industry, I still need to read its Methods and
Materials to see how each is implemented.
    To further complicate this discussion :) , there are also continuous
cultures that are run as turbidostats. To my knowledge and experience, there
are only two divisions for continuous cultures: chemostats and turbidostats.
Cell retention and/or recycle can then be employed in chemostats and are not
classified as types of continuous cultures.
    I have seen both what you call "semi-continuous" fermentations, and what
I have referred to as "fed-batch cascade" fermentations referenced in the
literature- both of which (upon examination) employ the same principle of
operation. Personally, I feel that the latter is more accurate in describing
the process since the word "continuous" in the former description implies
that the woking volume is constant in the fermentors (as opposed to where
the working volume is changing). Also, I have seen where a classical
continuous culture had intermittent feeding rather than continuous feeding
employed- the authors referred to their process as "semi-continuous" (there
were advantages in their final product in feeding the fermentors in this
    I would like to continue this discussion to hear of any different
"modes" or descriptions of fermentation you have come across in your career!

                                                    Dennis Bayrock

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