Hello everybody, I made 10x BG-11 medium for cyanobacteria. After autoclave, the medium became a little turbid. There is much precipitation at the bottom and it looked like Japanese Miso soup. Can it still be used for culturing cyanobacteria?
I have similar experience before but the media still worked for my Chlorella.
It is the matter of changing solubility of various mineral salts at high temperature. Some of them tend to precipitate when the temperature increases. It is very important to weigh all compounds accurately, check pH before autoclaving and adjust it if necessary. Precipitation of some mineral salts may slow down cyanobacteria growth but if you don't need to collect the biomass after certain number of days, it should be fine. Moreover, if you want to determine the content of some bioactive compounds in your biomass then it is better to avoid precipitates in the medium - only ionic forms of minerals are available to cyanobacterial cells. Precipitates dissolve in time but they still make the synthesis of some biomass compounds.
I agree with Lukasz, use an alternative method of sterilization which is sterile filtration.
Dear Fu Yen Jie,
Any media with ferric compounds in it will automatically develop hydroxide upon autoclaving which ultimately precipitates heavily when cooled down to room temperature. To eliminate this issue, add more or similar amount of EDTA prior to the addition of iron salts and then proceed to sterilization. A separate stock of iron salt in sterilized water can be prepared also by maintaining the concentration of the salt to be present in the final volume and this can also be added to the media after autoclaving. However, this method is rather laborious and tends to introduce errors to the stoichiometry of the media. Application of EDTA stabilizes almost all the salts in media except the ones where fixed nitrogen source in unintended. Using presterilized water you can also follow Lukasz's advice with success.
Thanking you,
Dr. Abhishek Mukherjee
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