I need to cultivate Chlamydomonas reinhardtii in an ammonium media with Air + CO2 3% bubbling. After growing very well, my cultures suddenly bleach and die. I do not have this problem with nitrate media.

Do you have an explanation for that?

The media i tried are Bold (with NH4) and TMP (with NH4) with Tris buffer (in order to keep a good pH with CO2 injection).

It is not a problem of N-deprivation because i added nitrate and more ammonium and the cultures also died at the same optical density. Moreover, microalgae shouldn't die following a N-deprivation (they bleach and stay alive for days).

It is not a problem of pH because just before the algae death, it is around 6,5.

It seems to be due to a toxicity but which one? Why don't I have this problem if I bubble only air ?

I really need to cultivate my algae on ammonium media because most of Chlamydomonas mutants are Nit- and cannot assimilate nitrate (i think that we shouldn't use nit- strains anymore because in nature, N is available mainly in the form of nitrate so we should grow microalgae on nitrate media if we want to cultivate them under similar conditions as in nature. But it is another matter of debate :-) ).

Any ideas?

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