THE ROLE OF PSEUDOLYSOGENY IN BACTERIOPHAGE-HOST INTERACTIONS IN A NATURAL FRESH-WATER ENVIRONMENT

Bacteriophages occur in high numbers in environmental ecosystems and a re thus significant mediators of microbial survival and activities. Ho wever, interactions between microbial populations and phages in si tu have been largely ignored. Current understanding of the process relies on studies performed with well-fed, laboratory-grown host bacteria. T he purpose of the experiments reported here was to determine bacteriop hage-host interactions under environmentally relevant conditions of nu trient limitation. These studies have revealed the importance of a phe nomenon called pseudolysogeny in the maintenance of viral genetic mate rial for extended periods of time in natural ecosystems. Pseudolysogen y is a form of phage-host cell interaction in which the nucleic acid o f the phage resides within its starved host in an unstable, inactive s tate. It is hypothesized that pseudolysogeny occurs due to the cell's highly starved condition. In such cells, there is insufficient energy available for the phage to initiate genetic expression leading to eith er a true temperate response or to the lytic response. However, upon n utrient addition, the pseudolysogenic state is resolved, resulting in either the establishment of true lysogeny or the initiation of the lyt ic production of progeny virions. The pseudolysogenic state may explai n the long-term survival of viruses in unfavourable environments in wh ich the infective half-life of their virions is relatively short.