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Free keywords:
phage-host system; immunity; lysogeny; pseudolysogeny; phage/bacterium ratio; coexistence
Abstract:
The influence of specific phages on the population size of their host bacteria was studied using a model system of a selected phage and its host bacterium, identified as Aeromonas sp. isolated from a lagoon in the southern Baltic Sea. For all initial phage/host ratios (PBR [phage/bacterium ratio] of 0.1 to 100), phage and host abundances reached a ratio of about 5 to 50 within the first 8 h. Interestingly, this range of phage/bacterium ratios of a single phage-host system corresponds to the ratio of virus to bacterial abundance found in natural habitats. The proportion of sensitive cells containing mature phage particles increased in the first 4 h to 40%, and then decreased (at rates dependent on the initial ratio) within 12 h (initial PBR of 100), 48 h (initial PBR of 10 and 1) and 72 h (initial PBR of 0.1) to less than 1%. There was evidence for rapid development of immunity (probably pseudolysogeny), especially at high initial phage concentrations. After 96 h incubation, carbon, nitrogen and phosphorus were added to improve the nutritional state of the bacteria. Although nutrients were added to all treatments when phage/host ratios were nearly equal, quite different reactions were observed for the bacteria populations with different initial PBRs. Those with low initial PBRs showed the most pronounced increase.
