Seasonal Variation in Lysogeny as Depicted by Prophage Induction in Tampa Bay, Florida

Abstract

A seasonal study of the distribution of lysogenic bacteria in Tampa Bay, Florida, was conducted over a 13-month period. Biweekly water samples were collected and either were left unaltered or had the viral population reduced by filtration (pore size, 0.2 m) and resuspension in filtered (pore size, 0.2 m) water. Virus-reduced and unaltered samples were then treated by adding mitomycin C (0.5 g ml ؊1 ) to induce prophage or were left untreated. In order to test the hypothesis that prophage induction was phosphate limited, additional induction experiments were performed in the presence and absence of phosphate. Induction was assessed as an increase in viral direct counts, relative to those obtained in controls, as detected by epifluorescence microscopy. Induction of prophage was observed in 5 of 25 (20%) unaltered samples which were obtained during or after the month of February, paralleling the results from a previous seasonal study. Induction of prophage was observed in 9 of 25 (36%) of the virus-reduced samples, primarily those obtained in the winter months, which was not observed in a prior seasonal study (P. K. Cochran and J. H. Paul, Appl. Environ. Microbiol. 64:2308-2312, 1998). Induction was noted in the months of lowest bacterial and primary production, suggesting that lysogeny was favored under conditions of poor host growth. Phosphate addition enabled prophage induction in two of nine (22%) experiments. These results indicate that prophage induction may occasionally be phosphate limited or respond to increases in phosphate concentration, suggesting that phosphate concentration may modulate the lysogenic response of natural populations.Lysogeny, the process whereby phage genomes establish silent infections in their host, is a common occurrence among cultivated bacteria of terrestrial (1) and marine (16) origin. Lysogeny can benefit the host by the process of conversion or the expression of phage genes, including genes coding for toxin production, antibiotic resistance, expanded metabolic capabilities, and homoimmunity (resistance to superinfection by the same or closely related phages) (19).The occurrence of lysogenic bacteria and temperate phages in the environment may be due to a variety of environmental and biological factors. Stewart and Levin (22) hypothesized that lysogenic interactions between viruses and host cells may provide a means of survival for viral populations that are threatened by poor host cell abundance and therefore cannot sustain population numbers through lytic infection alone.The importance of lysogeny as an alternative to lytic infection in natural populations of marine bacteria is poorly understood. Prior research in the Gulf of Mexico indicated that two-thirds of the marine environments sampled contained inducible prophage (6). Additionally, Jiang and Paul (17) found that 43% of marine heterotrophic bacterial isolates contained inducible prophage, indicating that lysogens comprised a significant portion of the heterotrophic microbial population. Conversely, other studies have d...

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