 Let's say you have successfully inserted a gene that codes for insulin, an alien gene that codes for insulin into a bacterial cell. Now the next thing you would do is to allow these bacterial cells to grow further so that we can extract more and more of insulin, right? So in a lab you do that in flasks or beakers like this but let's say you are asked to produce insulin to satisfy the insulin need of the entire country. Let's say you need to satisfy the insulin demand of the whole of India. How would you do that? Will you still use a small beaker to produce insulin? No, right? How about you use hundreds and thousands of beakers? Well that will be a very inefficient process. So in cases like that where we need to mass produce bioproducts, scientists use something called bioreactors. These bioreactors are nothing but large vessels that allows optimum growth conditions for bacterias or yeast or any small animal tissues or cells. So these bioreactors will help us to produce insulin on a large scale. So in this video we will talk all about bioreactors. We'll talk about this complex looking thing here. We will simplify it. We will look into its basic structure and see how it functions. Okay so let's begin. Let's begin by talking about the large bioreactor vessel. The vessel is cylindrical in shape. It is very sturdy and is made of stainless steel. It has a lead on top basically for pouring stuff into this bioreactor vessel. Now this bioreactor vessel which is a large vessel is connected to something called the control unit. This control unit is just like the brain and human beings. It is the brain of the bioreactor and it is called the brain because it controls everything that happens inside the bioreactor and it makes sure that the bioreactor is working properly. It has all the optimum condition for bacterial growth. Now that we have a big vessel for bacterial growth, let's put in some food for bacteria. Let's put in some food on which they can feed on and they can thrive. So the first thing that we have put into our bioreactor our food or we call it nutrients. And this nutrients contain water. It contains a readily usable energy source like glucose. It will have phosphorus. It will have carbon. It will have amino acids and it will basically have everything that cells require for proper functioning. Now that we have food for bacteria to grow, we can pour in bacteria into our medium or the broth that we have prepared. We can pour in bacterias now. But wait, what if the nutrients that we have poured in here, the culture broth that we have prepared is super hot. It is boiling. Well, some bacteria do survive boiling conditions but the bacteria let's say we are using E. coli do not survive boiling conditions. So for that we have to take care of the temperature of the nutrient medium. And who takes care of the temperature? The control unit. The control unit can sense any deviation in temperature. The ideal temperature for bacterial growth is around plus 20 to 60 degrees Celsius and any slight deviation is easily sensed by the control unit. So the control unit keeps a check on the temperature of the bioreactor. So the second thing that we have to take care of is the temperature of the bioreactor. Now the control unit can only sense deviations in temperature but it cannot change the temperature of the bioreactor. Well, there are various ways through which we can change the temperature of the bioreactor and one of the way is to have a water jacket around the bioreactor vessel. And in this water jacket hot or cold water is rushed into it and it has an outlet somewhere down here and whenever we put in hot water the bioreactor the bioreactor vessel becomes hot and whenever we put in cold water its temperature decreases. It is very much like the hot water bath we do in in the labs where we put in our test tubes in either hot or cold water according to how we want the content of the test tubes to be. Now that we have taken care of the nutrients, the temperature, what else do we need? What else do bacteria need for proper growth? Well, if the bacteria is an aerobic bacteria it will need air or oxygen to breathe in. And for that we need to have a supply of sterile air into our bioreactor vessel. Now initially we didn't fill the entire bioreactor vessel with nutrients. Remember we just filled three fourth of the vessel with nutrient medium and the space we left was for the air to come in and the air is pushed in with very high pressure. Well can you think of a reason why? Well the reason is the bacteria survive in the liquid part inside the bioreactor in the culture broth and they can only take up dissolved oxygen or dissolved air and only in very high pressure will the air get dissolved into the culture broth for the bacteria to take in. Now this high pressure is a reason why we use stainless steel as the material for bioreactor vessel over glass because it can withstand very high pressure. Now any slight deviation in the dissolved gas is sensed by again the control unit. So the control unit takes care of the gas within the bioreactor and the third thing that we have taken care of now is the gas within the bioreactor. With this we have taken care of the nutrient for the bacteria. We have taken care of suitable temperature, aeration within the bioreactor vessel. Now we can pour in the bacteria right? But wait won't it be a good idea to check the pH of the bioreactor vessel? Whatever the culture broth is highly acidic or what if it is very basic? Well the ideal pH for bacterial growth is around 4.6 to 7 but what if say the condition here is very basic? Our bacteria won't grow properly there right? So in situations like that we can always add in acids or bases so that we can adjust the pH and any deviation in pH is sensed again by the control unit right? So the control unit takes care of the pH. So the fourth thing here that we have taken care of is the pH of the culture broth. Alright with proper pH now everything seems suitable for bacterial growth. We can now pour in some bacteria into the bioreactor vessel and then allow them to grow. Well scientists have found out that even though the bacteria is multiplying to the bioreactor vessel they fail to get proper results. Well would you like to think of a reason why? Why even when the conditions are suitable they are not able to get proper yield? Well the reason is that the culture broth is not a homogeneous mixture. By this I mean the conditions everywhere inside this vessel is not the same. Let's say the bacteria that is growing somewhere here will have complete different conditions than the bacteria which is growing somewhere near the wall of the bioreactor vessel. Now you may think how is that even possible? Let me explain you how. As we are not mixing the culture broth it is almost stagnant and the bacteria which is present somewhere here is near to the source from where the air is pressurized. So this area will have high dissolved oxygen or dissolved gas. So the bacteria here will have high amount of dissolved air in it compared to the bacteria which is somewhere down there. And again the bacteria which is near the wall of the bioreactor will have other situations. Let's say we have pushed in hot water into this water jacket. So the conditions here will be boiling. So the bacteria which is present near the wall will be boiling whereas the bacteria somewhere near the center on top might have cold feet. So due to lack of homogeneity scientists were not able to get proper yield. And they overcame this problem by inserting an impeller into the bioreactor. This impeller as you can see has blades which rotates with uniform speed and mixes the culture broth. This impeller is quite similar to something that you must have seen your mom using in the kitchen. This utensil is very common in Indian kitchen. You must have seen your mother cooking dal or curry in it and she uses something like this a wooden long stick that has an ending like this that looks like the blade of an impeller. She holds it by the end dips it into the utensil and then rotates it. She does that so that the mixture inside becomes homogeneous. And the same thing is done by an impeller inside the bioreactor. Here your mother does this with her hand but in a bioreactor in a large vessel we have a motor that rotates the impeller. So as it rotates the culture broth no longer stays stagnant and every part of the culture broth will have same temperature, aeration and pH and that is how scientists get proper yield. And the homogeneity inside a bioreactor is so so important that this impeller is called the heart of the bioreactor. Now if you observe closely you can see that three sets of blades are submerged in the liquid inside the bioreactor while one set of blade is on top of the bioreactor which is also rotating but it is not mixing the culture broth. So what is its use? Well this blade is called the foam breaker and why do we need a foam breaker because we have foam inside the bioreactor vessel. Foam is formed at the interface of gas and liquid inside the bioreactor and it creates a havoc inside it. So we need a blade just to clear out this foam otherwise it will block most of the passages of the bioreactor it increases the pressure within the bioreactor and also when the bubbles of this foam burst it kills many bacterial cells along with it. So it is very important that we get rid of this foam and and the top most blade is just to clear out this foam. Now bioreactors that has an impeller to mix the culture broth are called simple steered tank bioreactor. Steered comes from the steering this impeller does within the bioreactor so quite quite makes sense right. Now there are bioreactors without an impeller. Now you may think that she just told us that an impeller is the heart of the bioreactor and now she is telling us that there are bioreactors without an impeller. Well the purpose of telling that an impeller is the heart is to tell you that how important mixing is. Now mixing can be done without an impeller as well. Let me show you how. Scientists found out another way of mixing and that is with the help of air bubbles. So the air bubbles are rushed inside this bioreactor it is pushed inside this bioreactor from the bottom and in the process it mixes the culture broth. So bioreactors that has a mixing system like this are called sparse steered tank bioreactor. Even here the steering is happening the mixing of the culture broth is happening not with the blades dough not with the blades of an impeller but by sprinkling air bubbles and sparse means sprinkling. So bioreactors in which the culture broth is mixed with sprinkling of air bubbles are called sparse steered tank bioreactors. Now how about you pause the video for a while and look at the screen in front of you it has all the parts that we just discussed how about you try and recall the functions of each of these parts and if you are stuck anywhere you can always rewind the video.