LLS phage grows less well on the recBCD deletion strain than on recBCD⁺ E. coli. (A, top) A suspension of LLS phage containing about 200 phages (pfu) was plated on ER1821 ΔrecBCD and ER1821 recBCD⁺ (wt). After overnight incubation at 37°C, photographs were made. (Bottom) Bacteriophage λ was used similarly as a control, showing that it grows equally well with and without RecBCD, as expected. Phages mouse 3, rabbit 1, and dog 1 behaved like LLS as expected because they have the same DNA sequence. (B) Growth curves show LLS requires RecBCD for optimal growth, but λ does not. ER1821 (recBCD⁺; round symbols) and ER1821 ΔrecBCD (star symbols) growing in tryptone broth at 37°C were infected with LLS (red symbols) or λ (black symbols) at an moi of about 0.01. Samples were removed at the indicated times into SM with CHCl₃ and titered on ER1821. Similar results were observed in a repeat experiment.