is minimal medium for MOPS minimal medium β-D-glucopyranose 20 g/l 3-(N-morpholino)propanesulfonate 40 mM ammonium chloride 9.5 mM ammonium heptamolybdate 3 nM borate 400 nM calcium chloride 0.5 µM cobalt chloride 30.0 nM copper sulfate 10 nM dipotassium phosphate 1.32 mM iron sulfate 10 µM manganese chloride 80 nM MgCl2 528 µM potassium sulfate 276 µM sodium chloride 50 mM tricine 4 mM pH Buffer zinc sulfate 10 nM The goals for this medium were to find a convenient and well defined composition that allowed varying all of the elements independently to facilitate isotopic labelling. This required using much less phosphate than in older media, which served roles of pH buffering and chelation of metals like Fe2+. For buffering, MOPS was used instead, with some Tricine added to help chelate Fe2+. E. coli can use MOPS as a sulfur source if not other sulfur source is added. However, sulfate easily outcompetes MOPS if both are present. To increase ionic strength and thus optimize the growth rate, NaCl was added. However, it is probably the case that KCl would work just as well, which would allow completely eliminating Na+ from this medium. morpholinepropanesulfonic acid (MOPS) minimal medium microbiological culture medium Escherichia coli K-12