Day 4 at BPT lab

Hello!!! It’s blogging time.

It's our day 4 and also one of our shortest labs. However, due to our school open house was clashed with the practical lesson, our teacher decided to show us the history plot on our day 2 instead of day 4… Our lab teacher, Ms. Ang showed us two different history plots (as shown below). They look very complicated and messy but…… they are very easy to understand. Trust me!


Let's start... History Plot... (click on the image for a clearer and bigger view)

All the parameter used in the fermenter was shown is the history plot… There are total 4 parameters! Blue and red lines refer to the temperature and pH value of the medium respectively and they are kept at constant for every moment. The green line represent to the rate of stirring speed. This line varies at different timing and the line fluctuates due to the amount of dissolved oxygen which represents by the cyan line. Hence, they are inverse relation. Let me explain more on each of the parameters.... LET'S GO..

1. Temperature:

Temperature was kept around 37 degree C as it is the optimum temperature for the cells to grow.


2. pH:

At the beginning, the pH has been constant for up till the 6th and 7th hour. The pH at that point has increased from 7.40 to 7.60. After increasing to 7.60, it remained constant throughout the entire experiment. From this we can deduce that from the 1st hour till the 6th hour, the cells in the fermentor are trying to adjust themselves to the inner environment and there isn’t any growth occurring during that period of time, this is also called the lag phase of the growth. But after this stage, the pH slightly increased. This can be due to the fact that the exponential phase of the growth is beginning. The pH then continue to be constant throughout in order to complement the growth of cells as any sudden changes in the pH may hinder the growth of the cells.


3. pO2:

At the beginning, the % of pO2 was 76 %. However, within the first two hours, the amount of pO2 dropped rapidly to 15% and we noticed that whenever the oxygen levels dropped to lows of 10 to 15%, it would then spontaneously shoot back up to 25 to 30%. This trend was observed throughout the rest of the experiment till the 24th hour. Why??
The reason for this continuous is caused by the cells inside the fermentor. As we all know that cells respirates and oxygen is an important factor to how well they grow and to also ensure their continuous growth whilst inside the fermentor. Therefore, due to the dissolved oxygen was consumed by the cells, the rise and drop of the oxygen levels is the cause of the fermentor trying to keep up to ensure a constant oxygen supply being provided to the cells. Each time the oxygen levels get low, it compensates by increasing the level of oxygen. This is done is by increasing the stirrer speed (rpm).

4. Stirrer speed (rpm)

At the beginning, the stirrer speed was at 200 rpm for 2 hours. It then slowly and gradually increased 350rpm with 500rpm being the fastest stirring speed ever recorded throughout. At 350 rpm, the speed then dropped to 225 rpm. This trend continued throughout the experiment. The reason for this is that the stirrer speed is very closely linked to the concentration of oxygen in the fermentor. When the oxygen levels in the fermentor gets low, the stirrer speed will then increase in order to generate more oxygen to keep up with the cells needs and also help to achieve better distribution of dissolve oxygen. By doing this, the amount of oxygen and stirrer speed corresponds with each other. If the amount of oxygen is low, the speed of stirrer will increase and vice versa.


Actually we can relate it with the cell growth curve.


Cell growth curve...

After adding the cells for few hours, the dissolved oxygen started to decrease slowly.
Why?? This is because the cells consume the oxygen. However at this time, the oxygen do not decrease very quickly as the cells are trying to adapt the new environment.
Thus they are not actively growing. This portion of graph is known as lag phase for the cell growth curve.

The fluctuation of stirring speed and dissolved oxygen in the history plot shows that the cells has adopt the medium whereby they have finish synthesizing all the required enzyme for the survival in the new environment and they are doubling; more cells are growing. This part is known as growth phase.
Lastly, the stirring speed will goes back to normal as cells in the fermentor did not used dissolved oxygen.


Summarized version is shown below.... (click on the image for clearer view)




Let's move on to 2nd type of graph...



(click on the image to view it more better)


The 2nd type of history plot is very similar to the first type of graph that I have mentioned as above. The only difference that there are two growth phase. The 2nd growth phase occurred when the growing cells feed on to those death cells for nutrient. There are inverse relation between dissolved oxygen and rate of the stirring speed.


It's time for me to stop here. Next week is our last fay of practical T_T. Let's everyone together.