Research Product

The persistence and interaction between newly isolated strains of Pseudomonas aeruginosa and resident bacteriophages indigenous to a freshwater environment was monitored over 45 days in lake water microcosms. The interaction between susceptible and resistant bacteria with pure phage (UT1) particles, or a mixed phage population (M1) was investigated by following temporal changes in host density, phage to bacteria ratio (PBR), and the appearance of apparent prophage carriers within the host population. Decay rates of the phage (UT1) ranged from 0.054 h-1 in natural water to 0.027 h-1 in filtered lake water. About 45% of sensitive bacteria incubated with phage UT1 were pseudo-lysogenic within 12 h of incubation in natural lake water. This process was delayed until 72 h in the sterile lake water control, suggesting that host-phage interaction is promoted in the presence of a viable natural microbial community. Phage UT1 appeared to stabilize the density of host bacteria in lake water at a level of 10 to the fourth power cfu ml-1. Bacterial coexistence with the mixed phage (M1) population resulted in an oscillating equilibrium with the (PBR) stabilizing at about 3. The presence of extraneous homoimmune phages appeared to be detrimental to the stability of the pseudo-lysogens, which were maintained at a lower population density than prophage-free cells in lake water containing the mixed phage (M1) population.