We are currently working with mixed bacterial cultures of CO-converting bacteria in completely inorganic media compositions. We have observed that changing buffer conditions (phosphate, carbonate or synthetic compounds) leads to enrichment of some members of the mixed culture, and its detrimental for others. Specifically, the addition of phosphate causes a tremendous shift in a Clostridium population, which decreases to almost undetectable levels (molecular detection methods applied).

I've read about the oxidizing effect of autoclaving phosphate together with other elements in the media (paper by Tanaka et al in AEM doi:10.1128/AEM.02741-14), however no autoclave sterilization is used for the media we use that will prevent formation of active oxides. We are also aware of "the accelerated substrate death" concept (early proposed by Gunter, 1954 http://jb.asm.org/content/67/6/628.full.pdf), that may cause the excess of phosphate in the media to some bacterial species. We work at 25 mM phosphate (highest concentration).

However, none of the above proposed effects fit with our data and probably other aspects need to be considered. Does any one know about any of these other aspects that should we be aware of and can help explaining our results?

Thanks in advance

Cheers