CALIBRATING ESTIMATES OF PHAGE-INDUCED MORTALITY IN MARINE-BACTERIA -ULTRASTRUCTURAL STUDIES OF MARINE BACTERIOPHAGE DEVELOPMENT FROM ONE-STEP GROWTH EXPERIMENTS

The timing of lytic phage development and the relationship between hos t generation times and latent periods were investigated by electron mi croscopy of one-step growth experiments in two strains of marine Vibri o species. Results were used in a correction factor developed to inter pret field studies of phage-infected marine bacteria. Both the number of mature phage per average cell section and the percentage of cells w ith mature phage increased exponentially by 73-86% into the latent per iods. Assuming that bacterial infection and lysis take place continual ly in the ocean, conversion factors for relating the percentage of vis ibly infected bacteria to the total percentage of the bacterial commun ity that are phage-infected were calculated as 3.70-7.14. When this ra nge of factors was applied to previously-collected field data [Proctor LM, Fuhrman JA (1990) Nature (Lond) 343:60-62; Proctor LM, Fuhrman JA (1991) Mar Ecol Prog Ser 69:133-1421 from 3 to 31% of the free-living bacteria and 3 to 26% of particulate-associated bacteria appeared to be phage-infected at any given time. Based upon a steady-state model i n which half the daughter cells survive to divide again, the percent o f total mortality would be twice the total percentage of phage-infecte d cells. From 6 to 62% and from 6 to 52% of mortality for the free-liv ing and particulate-associated bacterial community, respectively, may be due to viruses.