Team:Jilin China/Modeling

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As the picture shows, higher the concentration of formaldehyde is, the later the number of E.coli DH5αreach the lowest point. So at first the high concentration may not beneficial to the growth of the bacterias. But when they adapt to the high concentration, they can live longer compared to those in the lower concentration. Therfore, E.coli’s life span also depend on formaldehyde concentration. But no matter what the concentration is, E.coli will become inactive after 40 hours culturing.

According to Fig.2, FDH and PADH indeed have a great effect on degrading formaldehyde. In the first 3h, the concentration of formaldehyde drops quickly. 32% formaldehyde gas has been absorbed. In the later 5 to 7 hours, the absorbing rate starts to be slower. Finally, these two enzymes degrade 42% formaldehyde.

At first, we used UV absorption spectrum method with ultraviolet light, 660nm, to detect population of E.coli. As a result, due to the limited culture medium, the amount of bacteria would descend after 1.5h breed. However, most of the time, what determines the amount of E.coli is not the nutrient, but other conditions, such as living space or temperature. Because researchers can ignore the nutrient by adding more fresh culture medium. Thus, we picked up 11 points between 0 to 1.5h to structure growth curve (Figure 1) and aborted other points.

Figure 1. Growth Curve of E.coli within 0.3mM Formaldehyde.

Next step, we concentrated on the effect of formaldehyde absorption in first 1.5h growth curve. The results are as follows (Figure 2) (Figure 3).

Figure 2. Relative Content of Formaldehyde Absorption.

Figure 3. Relative Content of Formaldehyde Absorption.

Because it is hard to distinguish the degree of curvature in this curve by the human eye, we used a type of mathematical software to conduct it and obtained a derivative of each point, which could represent the speed of formaldehyde absorption (Figure 4) (Figure 5).

Figure 4. Derivative.

Figure 5. Derivative.

We can draw a conclusion according to Figure 3 and Figure 4 that before 1h the speed of formaldehyde absorption is increasing relatively dramatically compared with that in later half an hour. When it comes to the time between 1 to 1.5h, the speed maintains a steady level at 0.12. Overall, these features verify the growth curve (Figure 1) accurately, which means that 0-1h speed is due to increase of E.coli population, and 1-1.5h speed is because of steady amount of bacteria.