A comparison of the survival of F+RNA and F+DNA coliphages in lake water microcosms

The survival of seven F+ RNA phages (MS2 Group I ATCC type strain, two Group I environmental isolates, a Group II environmental isolate, a Group III environmental isolate, and two Group IV environmental isolates) and six F+ DNA phages (M13, fd, f1, and ZJ/2 ATCC type strains, and two environmental isolates) were examined in microcosms using a surface drinking water source. Phages were spiked into replicate aliquots of a source water at about 20,000 pfu/ml. Replicate spikes were incubated at 4 and 20 degrees C and monitored for 110 days. At 4 degrees C, Groups I and II F+ RNA phages were detectable through 110 days, with reductions of about 1 and 3 log(10), respectively. The Group III F+ RNA phage demonstrated 5 log(10) reduction after 3 weeks, and the Group IV F+ RNA phages were reduced to detection limits (5 log(10) reduction) within 10 days. Of the F+ DNA phages, all four type strains were detectable with about 2.5 log(10) reduction after 110 days at 4 C. The F+ DNA environmental isolates were detectable with about a 4 log(10) reduction after 110 days at 4 degrees C. All phages demonstrated faster decay at 20 degrees C. These results suggest that differences in F+ phage survival may influence their prevalence in environmental waters and the ability to attribute their prevalence to specific human and animal sources of faecal contamination.