We expected the transformed PCC7942 with CrtZ gene could produce zeaxanthin and become more yellow. Just like our prediction, the result showed that the transformed PCC7942 was more yellow than wild type obviously.
Moreover, we expected the transformed PCC7942 which produce zeaxanthin would change wavelength absorbance and have better photosynthetic efficiency.
Wavelength Absorbance
To test this hypothesis, we used spectrophotometer to measure the absorbance of CrtZ and wild type at 400 to 700 nm. The outcome was that the OD value of CrtZ at 400 to 500 nm was hihger than wild type. The result verified our first prediction, a change of wavelength absorbance. Not only this, the change of wavelength absorbance was at 400 to 500 nm, which was blue light. This indicated CrtZ absorbed blue light and reflected yellow light, so CrtZ was more yellow than wild type. The measurement matched what we saw intuitively.
Photosynthetic Efficiency
To test whether the photosynthetic efficiency of CrtZ is better than wild type, we used iodine to measure starch concentration. First, the initial concentration of microalgae of CrtZ and wild type should be same, so that the measurement could be fair. We measured the OD value at 730 nm, which represented the concentration of microalgae. Then we calculated how much microalgae and BG11 (the medium) we should add to make same amount of microalgae in each plate. Second, we started to measure starch concentration. We measured the OD value of each plate at 730 nm, which represented the cell number. Then we added 50 μl iodine into each cuvette, waited for five minutes, and measured the OD value at 620 nm, which represented the starch content. We repeated this step for seven days. Here are our results.
Then we divided the starch content by cell number, and we knew there was how much starch in every unit cell.
Then we calculated the variation of starch content per cell per day.
The first day, wild type (WT) had more starch than CrtZ. However, the increase of starch per day of CrtZ was more than wild type. The result implied that CrtZ could produce more starch per day than the wild type. Moreover, the result corresponds to our hypothesis -- CrtZ actually had better photosynthetic efficiency!
Survival Ability
We also considered about the survival ability of CrtZ. Therefore, we conducted a competitive experiment of CrtZ and wild type. We co-cultured CrtZ and wild type together, and then observed the color after seven days. Similarly, the initial concentration of microalgae of CrtZ and wild type should be same, and we used the same method we used in photosynthetic efficiency experiments.
After seven days, CrtZ and wild type both survived. The result indicated that CrtZ was strong and had great survival ability!
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