e.coli-killing infection

[R Hanemaaijer]

Dear netters,

Help !!
we have a rather big problem with our E.Coli (both XL-1blue MRF' and 
JM109). When we grow them, they behave normal untill they reach an 
OD550 of 0.4. From that moment on in 10 minutes time the OD550 drops 
to less than 0.1; the medium gets clear with undefined precipitates.
When we grow them further over-night the culture is full grown (OD550 
is more than 2.0), but we can not infect them anymore with helper-
phages.
Can the reason be a lytic-phage?, and, if so, does anybody know how 
can we get rid of them. (We grow M13-phages so we need a F-pilus on 
the cells) Any suggestions are welcome!!

Annette van der Goes,
graduate-student, Leiden.