agar polymerization - (Jun/24/2009 )

Hello everybody!

I was wondering what could stop agar from polymerizing?
I poured plates (5g agar, 0,9 g NaCL in 100ml H20) and left them to polymerize but in 24 hours they are still half liquid! What did I do wrong?

(i) you forgot the agar (happens more ofthen than you might think).

(ii) if you are only using 5g per 1000mL you will only get a slurry. Usually 15 - 20 g per L are added (or are you really using 50 g/L?????).

(iii) your autoclave is not working and the agar did not dissolve.

(iv) the pH of your solution is to low. Agar does not polymerise at a pH smaller 4.5 (or was it 4?)

Agar is composed of polysaccharides that do not polymerize - they gel. The pH where is hydrolyzes and will not set is < 3.

GeorgeWolff on Jun 24 2009, 10:56 PM said:

You are right....sorry for sloppy language.

Thanks for refreshing the pH! Nevertheless when making media with a pH lower than 4.5 I would suggest to add some more agar (especially if you want to plate sth on it).

yes, I really use this much, the plates are not for culturing anything but to glue tissue to while making slices.