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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.