How to measure the amount of algae using a spectrophotometer

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ElenaToffanin
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How to measure the amount of algae using a spectrophotometer

Post by ElenaToffanin »

Dear Science Buddies
I am a Junior at the Awty International School of Houston and as part of the IB curriculum, I am writing a research paper on the affect of fertilizers on cyanobacteria. I am having trouble finding a way to measure the amount of algae present in the solution. I was hoping you could help me. I did find that the spectrophotometric method works but I can't seem to find the exact procedure behind this method.
Thank you so much in advance for your time
Elena
SciB
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Re: How to measure the amount of algae using a spectrophotometer

Post by SciB »

Hi Elena,

I did a search for cyanobacteria culture to see if i could find a description of the method for spectrophotometric measurement of bacterial concentration in liquid cultures. I found one paper that does use a spec to measure the bacteria, but it is really technical:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934312/

I read the method section under Growth Rate and the researchers did use a Shimadzu UV-Vis spec for some measurements. The bacteria were homogenized before the reading. What I was specifically looking for was the wavelength of light that was used to measure absorbance of the bacteria and I could not find it in the Method. Scrolling down further in the paper, I found a figure, Fig. 6, which shows the absorbance of the bacterial pigments and the wavelengths tested and the main peak was at 678 nm.

Since chlorophyll is the molecule that you would be measuring the absorbance of using a spec, you could do a search for spectrophotometric measurement of chlorophyll and see what you come up with. If I were doing this, I would use the scanning feature of the spec to scan the wavelength range of say 400 to 800 nm and see where the peak absorbances (Abs) are. Then you could use the peak Abs to measure the amount of chlorophyll in the cyanobacterial culture. You would still have to do a bacterial count on agar plates in order to convert the Abs reading to actual bacterial numbers.

If you need help with the details of this, let us know and we will try to make it clear.

Good luck!

Sybee
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