Lidstrom:MM1/MM2/MM3/HY

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What is the difference between MM1/MM2/MM3/HY?

• They all have the same trace elements solution. The primary difference is the nitrogen source:
  • MM1/HY uses ammonium
  • MM2 uses nitrate
  • MM3 has no added nitrogen
    • MM3 is used when growing on methylamine, which releases N as it is metabolized
• FYI, the trace elements are added after autoclaving for both liquid and agar formulations. Thus it is possible there could be contaminants before you start an experiment.

If all organisms assimilate N into biomass as NH4+ why do we give them MM3?

• This is an interesting question, as the organisms must convert nitrate (NO3-) into ammonium to assimilate it. Two likely factors:
  • Ammonium is too toxic
    • In methanotrophs, it interferes with pMMO (methane assimilation enzyme). We don't have a tested hypothesis for why ammonium would be toxic to methylotroph.
  • They prefer to convert nitrate to ammonium (using NADH) to release energy, as they have an excess of NADH due to their metabolic strategy.

Why don't we have a media with nitrite?

• It is toxic.