An autolytic system based on a thermally inducible phage lambda, λHL1, has been applied for the recovery of poly(3-hydroxybutyric acid), PHB from a recombinant E. coli, XL1-Blue.
The lytic capability of λHL1 was evaluated in flask culture for a lysogen, XL1-Blue(λHL1) which had been constructed by infecting XL1-Blue with λHL1. When the optical density at 600 nm ($OD_{600}$) of the culture broth reached 0.2, cell lysis was induced by increasing the culture temperature from 30℃ to 42℃. We observed that the $OD_{600}$ decreased to a negligible level in an hour after the thermal induction, as most of the cells were destroyed by the autolytic system.
A series of flask cultures were also carried out with XL1-Blue(λHL1, pSYL105) which had been constructed by transforming XL1-Blue(λHL1) with pSYL105, a plasmid containing PHB synthesis gene. We observed that the lytic efficiency was about 80% when thermal induction was done at an $OD_{600}$ of 0.2, and that the existence of the plasmid in the cells inhibited to some extent, the lytic capability of λHL1 even with no significant level of PHB accumulation. When we tried thermal induction at an $OD_{600}$ of 0.34 - 0.4, only a low level of lytic efficiency of less than 60% was observed. We tried chemical induction in addition to thermal induction to obtain a much better lytic efficiency.
In another series of experiments with XL1-Blue(λHL1,pSYL105), we investigated the interaction between the expression of λHL1 and the accumulation of PHB in the cells. The lytic efficiency decreased significantly from 60% to 30% as the induction was delayed from at 6 hours to at 12 hours to allow more PHB to accumulate in the cells. Also, the existence of λHL1 in the cells was found to inhibit to some extent, PHB accumulation.
