Hello!
I measured an unknown strain of cyanobacteria growing in suspension at 730 nm. What exactly is measured at 730 nm, though?
And can anyone explain to me please, why OD 730 drops when the cyanobacteria is put under limitation and increases again after sometime? Is there some type of downregulation of the protein that is measured at 730 nm?
I've also read about people using OD 750 nm and 655 nm. What is measured at these wavelengths and when should you use these instead?
Thanks and regards
When you do OD to follow microbial growth, what you are trying to measure is not actually optical density, but turbidity. In other words, the light not reaching the detector has not been absorbed, but deflected/scattered by the cells in suspension. This has two important practical implications:
So, in your case, you can use 730 nm, 750, 655, whatever, as long as a) it is not actually absorbed by the cells or the culture medium, and b) you use it consistently.
Hope it helps!
Thank you very much, this is helpful to know that I am measuring turbidity instead of optical densitiy. I must take that into consideration. I also know that 730 nm works for this type of cyanobacterial culture. I more wanted to know which molecule I am measuring here...is it chlorophyll a? And which other molecules are measured at the other wavelengths. May be, that I am completeley on the wrong track here...
1. Since you want to measure cell numbers, you should use a wavelength that is NOT specific for a cetrtain molecule (e.g. chlorophyll). Otherwise you cannot be shoure whether a change in your OD reflects "more cells" ore "more chlorophyll per cell". I would use 750 or 800 nm.
2. You should check wether the detector response of your instrument is linear (number of cells vs. OD measured
3. For filamentous cyanobacteria this method is very problematic. Works best with unicell.
I agree with both responses, but especially with Gerd response. I would add that cyanobacteria contain chlorophylls plus phycoerythrin and other cyano-specialized pigments. These pigments can be very affected by nutrient limitations, which means that the pigment cell content is different depending upon environmental conditions. To prevent biais in your measurements due to pigment cell content you need to take measurements with wavelengths that do not interfere with the pigments' absorption spectra. And for that you need to be above 750 nm. Also, it's good to get calibration with cell number or cell bio-volume vs spectro signals in relation to environmental conditions, otherwise you objectively cannot compare growth curves and "OD intensity" between conditions.
Also, for filamentous cyanobacteria, there is NO good method, it is difficult everytime. So best is multiplying measurement types to get more robust results.
Good luck!
As above. You want to measure any wavelength >700nm because you are interested in light that is scattered (turbidity), but not absorbed. The method is in no way chemically specific, but rather measures the abundance of particles (including cells) in suspension. This is a reliable, easy, robust method for routine monitoring of cultures. It is not, however, a good method for answering specific research questions regarding the how's and why's of cell growth.
Good Luck!
The growth rate (K) and doubling time
(G) were obtained according to the
following equation:
(log ODt- log OD0
K =-------------------------------- x 3.322 [15]
t
0.301
G = -------------------------- [16]
t
T: time (day)
ODt: Optical density after (t) day
ODо: Optical density at beginning of
the experiment zero time
15. Huang X.H., Li, C.L., Liu, C.W. and Zeng, D.Q. 2002a. Studies on the Ecological Factors of Oocystis borgei. J. Zhanjiang Ocean Univ. 22(3): 8-12.
16. Huang X.H., Li C.L., Liu C.W., Wang, Z.D andChen, J.J. 2002b. Studies on the N and P nutrient demand in Nannochloris oculata. Mar. Sci. (China). 26(8): 13-17.
for me I have used 760 nm for turbidity and for filamentous cyanobacteria I had used Kroll Ultra-Turrax homogenizer to give uniform and stable suspension before growth measurements.I had selected 760 nm away from absorping pigments.
O.D can be used as an indirect measurement of biomass for microalgal cultures. In some species pigment content such chlorophyll a vary with age and culture conditions - such as nitrogen limitation which can lead to increase in pigment content.
This could introduce error in biomass measurement due to absorbance by the pigment. So by selecting a wavelength that reduce absorbance by the pigment , the error can be minimized. 750 nm is best where chlorophyll a is the main pigment in the species being studied, as the absorption maxima of chlorophyll a is 665 - 680 nm
Ahmed Darwish El-Gamal Hi!!
How can you used the Kroll Ultra-Turrax homogenizer?
I will use filamentous cyanobacteria and for detecting spesific growth rate I dont know what I do. can you mange this? and how?
Gerd Kloeck Hi!
Your answer is helpfull, thank you. Do you have any solution for detecting culture growth of filamentous cyanobacteria?
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