Occurrence of lysogenic bacteria in marine microbial communities as determined by prophage induction

Abstract

Viruses are abundant and dynamic members of the marine microbial community, and it is important to understand the11 role in the ecology of natural microbial populations We have previously found lysogenic bacteria to be a significant proportion (43%) of the cultivable heterotrophic microbial population. As the majority of marine bacteria are not cultivable using standard plating methods, we measured the proportion of marine lysogenic bacteria in natural communities by prophage ~nduction. Mitomycin C, UV radiation, sunlight, temperature and pressure were used to induce prophage in lysogenlc bacteria from estuarine, coastal and oligotrophic offshore environments. To determine ~f hydrocarbon pollutants may cause the induction of marine lysogens, aromatic and aliphatic hydrocarbons (including Bunker C #6 fuel oil, phenanthrene, naphthalene, pyrene, and trichloroethylene) were also used as inducing agents. Induct~on was most often found in estuarine environments, where viral direct counts increased from 128.8 to 345% of the uninduced control, resulting in mortality of 10.5 to 67.3% (average 34%) of the bacterial population. Up to 38% of the bacterial population was lysogenized in estuanne environments, as calculated from an average burst size. Microbial populations from oligotrophic offshore environments were inducible at 3 of 11 stations sampled. Eight of the 11 samples (73 %) treated with polyaromatic hydrocarbons resulted in prophage induction in natural populations. Time series analysis was also conducted in 2 samples induced by mitomycin C from the Atlantic Ocean near the coast of North Carolina, USA. For both samples, significant decreases in bacterial numbers were detected in treated samples after 8 h of incubation. A significant increase of viruses was detected a t 8 h at one station and at 24 h at the other station after induction. This study indicates that natural lysogenic populations are sensitive to a variety of ~nduc ing agents, and induction occurs more frequently in coastal and estuanne environments than offshore environments.