Temporal variations in the concentrations of bacteria and their lytic phages: an example of an indigenous phage host system in Lake Plu?see, Germany

摘要

1. We describe the abundance of an autochthonous alphaproteobacteria Sphingomonas sp. and its lytic phages during a period of about 3 months in Lake Plu?see, Northern Germany. This is the first report of a specific autochthonous phage host system of a heterotrophic bacterial strain in a natural freshwater environment. 2. The concentration of bacterial hosts (Sphingomonas sp. strain B18) fluctuated between 20 and 1,150 (median 168) colony-forming units (CFU) mL~(-1) and the concentration of the specific lytic phages ranged from 20 to 680 (median 110) plaque-forming units (PFU) mL~(-1). Different Sphingomonas sp. strains were isolated, showing different sensitivity against two phage isolates. The specific virus to bacteria ratio (VBR) varied by a factor of about 280 and ranged from 0.03 to about 8.5 (median 0.6). 3. Encounter rates of 0.0007 to 0.198 d~(-1) (median 0.03 d~(-1)) were calculated from the measured concentrations of Sphingomonas sp. and its lytic phages. From changes of PFU between two consecutive samplings net phage decay rates in a range between 0.003 and 1.3 d~(-1) (median 0.26 d~(-1)) were calculated. 4. Concentration factors were calculated which enable sufficient encounter rates to explain the concentrations of bacteria and their phages. 5. The results of Kokjohn et al. (1991) support the suggestion that the explanation of the coexistence of lytic phages and their host bacteria by the used encounter rate model needs to be revised.