Increasing cell growth rate in plain M9 medium - (Oct/05/2012 )

I have been trying to grow E. coli DH1 transformed with various plasmids in "plain" M9 medium, ie. this recipe with thiamine and NO other supplements like casamino acid, iron, trace metals etc. I've adapted the cells by subcultivation 3x but the growth rate is still significantly slower than rich media like LB. Adding casamino acid definitely increased growth rate but I don't want to use it because I want a real defined media. Are there other ways to increase the growth rate? Would adding iron and/or trace metals help?

Indeed, casaminoacids it's something I would avoid as it makes the media undefined.

Some M9 variations include different aminoacids and most of them include also proline (e.g. M9 with arginine includes Arg and Pro).

You may also try supplements of trace elements, very common in minimal media. Some of this solutions have even their own name such SL-6 or SL-10 trace element solutions, Wolfe's mineral solution, Wolfe's vitamin solution... and you may find easily recipes