Debunking the dogma that RecBCD nuclease destroys phage.

For decades, it has been repeatedly claimed that the potent bacterial helicase-nuclease RecBCD (exonuclease V) destroys foreign (non-self) DNA, such as that of phages, but repairs and recombines cellular (self) DNA. While this would constitute a strong host-survival mechanism, no phage destroyed by RecBCD is ever specified in those claims. To determine which phages are destroyed by RecBCD, we searched for phage isolates that grow on Escherichia coli ΔrecBCD but not on recBCD+. In contrast to the prevailing claim, we found none among >80 new isolates from nature and >80 from previous collections. Based on these and previous observations, we conclude that RecBCD repairs broken DNA that can recombine but destroys DNA that cannot recombine and recycles the nucleotides.