Cell lysis after IPTG induction?

I'm expressing a recombinant protein in e.coli BL21pLyss strain using pET expression system. After adding IPTG (final conc. 0.1, 0.3, and 1mM) at OD600 = 0.8 in TB medium, cells were lysed after a few hours of induction at 37C. Transformants without IPTG kept growing. Does someone have Read more Read less