Significance of lysogeny in the marine environment: Studies with isolates and a model of lysogenic phage production

The importance of lysogeny in marine microbial populations is just beginning to be understood. To determine the abundance of lysogens in bacterial populations, we studied the occurrence of lysogenic bacteria among bacterial isolates from a variety of marine environments. More than 116 bacteria isolated on artificial seawater nutrient agar plates were tested for the presence of inducible prophage by mitomycin C and UV radiation. Induction was determined as a decrease in culture absorbance at 600 nm, after treatment with inducing agents. Samples in which optical density decreased or remained the same after induction were further examined by transmission electron microscopy, for the presence of virus-like particles. More than 40% of the bacterial isolates contained inducible prophage, as determined by mitomycin C induction. A higher percentage of lysogenic bacteria was found in isolates from oligotrophic environments, compared to coastal or estuarine environments. These studies suggest that lysogenic bacteria are important components in marine microbial populations. However, a mathematical model based on viral and bacterial abundance and production rates suggests that, under normal conditions, lysogenic viral production contributes less than 0.02% of total viral production. Therefore, lysogens in the marine environment may serve as a source of viruses and only contribute significantly to viral production during natural induction events.