The lysis may not be due to a phage infection of your strains. I have
worked on a couple of cases where BL21(DE3) did not like the expression
of specific proteins which we were trying to express and indicated their
displeasure with lysis shortly after induction. If you're not inducing
and still getting this, then try using the pLysS or pLysE versions of
the cell which will close off any leaky expression of your system. You
may also find that growth at lower temperatures or varying the OD of
induction might help.
You never mentioned whether this happens with all plasmids which you
have transformed or just the one. If only with the one, then I think
that it is a toxic protein problem (check out a reference, which I don't
have, on the trials of expressing the R Domain of CFTR in bacteria). If
this happens with all vectors including something like pGEX or pUC, then
your cells may indeed be faulty and you should try repeating the
experiment with cells from another lab.
Randall C Willis, Researcher
Biochemistry, Hosp for Sick Children
3522-555 University Ave.
M5G 1X8 CANADA
416-813-5933 (ph) -5022 (fax)
willis at gandalf.psf.sickkids.on.ca