Tuesday, March 19, 2013

Plant Bio Reactors (PBR)

You might be aware of using E.coli for producing human proteins. E.coli is a well established expression system and easy to handle. And many people are working on this E.coli (even I'm handling only E.coli in my laboratory most times)

Okay, we are fine with E.coli, and we are producing our protein of interest in that. And what is the need for an eukaryotic expression system? That thing, I explained in one of my previous posts (Clone human genes into plants!)

I explained in that post like we are expressing our human proteins and we are growing the entire plant for obtaining our protein of interest. And we need not do that all time and there is a choice of growing plant cells in bio reactors!

Yes, we do grow E.coli in bio reactors and why not the plant cells? You might be aware of this plant bio reactors and here I'm going to share something that I know about them. 

Plant bio reactors

I attended a seminar on "Advances in plant biotechnology" and as you guessed, this post is the result of that.
Okay, let me jump into the topic.

Important factors to be considered while designing a PBR are:
  • Plant cells (as well as animal cells) are shear sensitive
  • Plant cells form aggregates - and this aggregate formation sometimes helps you with your production
  • Risk of contamination

 I consider that these three things are very important in growing your plant cells in a PBR.

Shear sensitivity:
As, the plant cells are shear sensitive, we can't use the same reactor which we use for growing our microbes for growing plant cells. If you use a super fast impeller for effective mixing to eliminate the mass transfer limitations, then I'm sure your plant cells are gonna die. So, special design is needed for growing the plant cells.

So, there must be a balanced mixing such that the mass transfer is good and also the cells should
not lyse!

Aggregate formation:
Plant cells also form aggregates like bacterial cells. We don't prefer aggregate formation in case of bacterial cells. But, in plant cells, depending on the species, this aggregate formation could improve our productivity.
On the other hand, this aggregate formation causes mass transfer limitations thus affecting your productivity.

"???" You feel like "oh God"? And your question is "whether to have aggregates in plant cell reactors or not?"

Let me answer you. You need to have aggregates if it benefits you with your productivity but the same time, the mass transfer must also be good. For having the two things in balance, we have to maintain a "particular aggregate size", so that, our productivity will be fine in both the aspects like mass transfer is good and aggregate formation improving the productivity.

Then, the next question may be "how to maintain the optimum aggregate size?"

The optimum aggregate size could be maintained by using immobilization technique. You could immobilize your cells i.e. the optimum aggregate size would be maintained using immobilized plant cells.

Risk of contamination:
Comparing the bacterial cells, plant cells have a very high risk of contamination. Even when we grow them for producing callus, there is a lot of contamination risk especially fungal infection.

So, growing them in a reactor, that will be difficult job especially in case of maintaining the sterile environment. Most times, continuous reactors are not used for bacterial cultures as it has high risk of contamination comparing the batch and fed batch. I had never seen or done continuous culture of bacteria in our lab, normally we don't do continuous culture as it goes for more than a day and also it is difficult to maintain sterility. And, even when on of my seniors wanted to try continuous culturing, we were all saying "no you better try batch instead" fearing that everything may get spoiled due to contamination.

But, if high sterility is maintained, you can do continuous culturing of plant cells also.

Hope you understood what i explained, got doubts? Comment or e-mail, will answer you as soon as possible.

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