We are doing some experiments on plastic-degrading microbes, growing them on M9 salts with plastic as the sole carbon source. We buy the M9 salts from Sigma.
According to the formulation, the only cations are Na, K, ammonium, Ca, Mg and the only anions are phosphate, sulfate and chloride.
Trace elements such as Fe, Zn, Cu, etc are not mentioned. Nonetheless, M9 medium works fine, although we do find the microbes grow better if we reconstitute the media with tap water instead of distilled water.
Can anyone clarify this conundrum? Do the trace elements perhaps just follow along as impurities in the components?
I don't work on microbes or M9 media, so can't say much specifically, but I would guess that there would be some trace elements at the parts per billion level, for example Sr often accompanies Ca, due to their similar chemistry etc. Unless you get your M9 stock analysed for other elements, you won't be sure what else might be in there, so go to your friendly analytical chemistry lab and have it analysed.
Tap water will definitely have a range of anions present, from the copper piping at least, but also reflecting the water source and storage (rivers, lakes, dams, tanks etc). Even distilled water will have some trace elements, but possibly not at biologically significant concentrations.
Microbes need a range of trace elements, so I'm not surprised yours grow better with tap water than distilled water. Not knowing the conditions and scale of your experiments you want to use to degrade plastic, I would not presume to suggest any recipes for you, but I would highly recommend investigating whether trace elements could help your microbial growth.
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