Dear, Jesús Perales-Adán

you can use "Glass capillary method" to isolate and purify cyanobacterial/microalgae culture.

First of all you take a sterile glass capillary tube, put it on the burning sprit lamp/ fire flame with hold it to both end of capillary then stretch it and break it into two parts and create a hair like capillary tube from the center, break end portion of capillary tube with the help of sterile forceps.

Further, take a cyanobacterial growing on agar petri dish, open it in the surrounding of fire flame and select a single cyanobacterial colony with the help of hair like end of glass capillary tube and transfer it into a fresh media (You have selected; BG-11/BBM or others). Repeat it 2-3 time then you will got pure cyanobacterial culture.

I have attached picture of glass capillary tube below.

Best Wishes.

We have used an antibiotic method to produce axenic alga cultures. This might work with your cyanobacterium. If you talk to a microbiologist, they have a kit used to test sensitivity of bacteria to many antibiotics. Your culture is spread on agar and different paper disks containing different antibiotics are placed on the agar plate. Look for a clear zone around a paper disk where the bacteria are killed but your cyanobacterium is not affected. This tells you which antibiotic to add to your culture medium. Our technique was published previously as “One step antibiotic disk method for obtaining axenic cultures of multicellular marine algae.” Bradley et al. 1988. Plant cell, tissue and organ culture 12: 55-60. Available on Peter Bradley’s ResearchGate place. Good luck with your work.

Cover the bottle with the algae-bacteria suspension to avoid radiation of light except the neck of the bottle.

Store the bottle into sunlight for a few minutes. The cyanobacteria will concentrate at the bottle neck.

It won‘ t be free of bacteria but the cyanobacterial ratio will be increased in comparison to the number of bacteria.