BL21 question

[Chen Ho An]

Does anyone know from which strain is BL21 derived from?  I'm asking this
because the Health & Safety people here thinks BL21 is unsafe because it
is not a K12 or B strain derivative and do not have sufficient evidence
of its disablement (don't know what that means or refer to - probably
refer to the transmissibility of the plasmids).  We may not therefore use
it in the future.  I've always thought that BL21 is a B strain derivative
but it seems I'm wrong, so, what is it derived from?

p.s  does anyone knows of other good expression strains?




--