Maryam Taat's Bacteria & Fungi Page


Bacteria & Fungi Growth


My bacteria plate was kept in my kitchen, where the temperature was usually around 70-75 degrees Farenhiet. The spot it was placed in was located right next to a window, so it was exposed to sunlight everyday. The container was opened for one hour on the first day and for 10 minutes each day after that at around 7:15 AM. The bacteria in my plate was MM (minimal medium). This experiment was conducted over a time period of 15 days in September, 2015. 

Results 1: Total Number of Colonies 

Table 1: Total Number of Colonies

 Day                 Total # of Colonies 
 1 0
 2 4
 3 7
 4 13
 5 14
 6 20
 7 21
 8 23
 9 30
 10     31
 11 26
 12 35
 13 34
 14 31
 15 41

Figure 1: Graph of Table 1

Results 2: Individual Colony Growth 

Table 2: Growth of Individual Colonies

 Day  Type 1
(black)
 Type 2
(gray)
 Type 3
(white)
 Type 4
(beige)
 Type 5
(orange)
 1 0 0 0 0 0
 2 0 1 0 3 0
 3 0 2 5 0 0
 4 2 6 4 0 1
 5 2 6 5 0 1
 6 3 9 8 0 0
 7 3 10 8 0 0
 8 3 13 7 0 0
 9 3 20 7 0 0
 10 3 21 7 0 0
 11 3 16 7 0 0
 12 3 21 11 0 0
 13 3 24 7 0 0
 14 5 19 7 0 0
 15 4 31 6 0

Figure 2: Graph of Table 2 

Conclusion 

My bacteria plate was an example of logistic growth. In the first 9 or 10 days, the bacteria grew at an increasing rate. However, after the 10th day, the growth rate started slowing. In the last 5 days, the total number of colonies rapidly decreased and increase, suggesting that the population had reached its carrying capacity and resources had become limited. This is also probably why the bacteria growth did not cover the entire plate. In the first way I summarized my results, I counted the total number of colonies that were present each day. My first table shows that the number of colonies had reached 31 in the first 10 days, and then started decreasing. After the first 10 days, the total number of colonies stayed between mid 26-41. Therefore, the carrying capacity is probably around 30-35. After the population reached the carrying capacity, it started to decrease and increase at an unsteady pace. Eventually, the population would've leveled out and stayed closer to the carrying capacity. In the second way I analyzed my results, I counted the number of different types of colonies. I found that the decrease in some types colonies was caused by specific colonies turning into another type of colony. This was most common in white colonies that became gray. Most of the colonies were gray and very small. 


What I learned 

During this experiment, I got to witness the logistic growth of a population up close. I learned that logistic growth can occur in all types of living organisms and not just in animals. Even though the bacteria population was relatively small, it still reached carrying capacity and some colonies died off because of it. If there wasn't competition for the limited resources, such as space, the colonies would've continued growing. 
 


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