Jake Daniels

The buffer we are using is HEPES buffer, the precipitate forms with it and without it

Sorry forgot to add some info! We've checked the pH of the media throughout the adding of the Iron stock solution and the pH stays <7. The buffer isn't in the CAA medium already but is what the FeCl3 is currently dissolved in instead of H2O. 2.6g/10ml was what we used to make a concentrated Iron Supplemented CAA medium before and have since tried lower concentrations, currently on 1g/L however no change in concentration seems to change anything. Precipitate seems to form at higher and lower concentrations of FeCl3 so some reason. One of my project supervisors says it's common for iron supplementation in CAA media to add FeCl3 and we are going off of a specific paper, although I am unsure which one. Just a bit strange that it's worked before in exactly the same conditions but we can't figure out why it's happening now or what might have changed. Thanks for your response!

I'm currently doing an undergrad project where we're trying to create 3 CAA (casaminoacid) media's (one iron limited, one plain CAA, and one iron supplemented). We created an iron supplemented media by adding 10ml of 2.6g/10ml of FeCl3 (dissolved in ddH2O) to a bottle of 200ml of CAA media (made up of 4g of CAA, 0.944g of K2HPO4•H2O, and 0.2g of MgSO4). This worked and the media appeared clear. Every subsequent time we've attempted to make this, as soon as the FeCl3 stock solution is added a precipitate forms and we can't figure out why, we've tried adjusting for a more acidic pH but it still happens and it also occurs in other medias like TSB. This also occurs before the K2HPO4•H2O and the MgSO4 has been added in. Any help would be appreciated! Thanks!