Occurrence of lysogenic bacteria in marine microbial communities asdetermined by prophage induction

Abstract

Viruses are abundant and dynamic members of the marine microbialcommunity, and it is important to understand their role in the ecology ofnatural microbial populations. We have previously found lysogenic bacteria tobe a significant proportion (43%) of the cultivable heterotrophic microbialpopulation. As the majority of marine bacteria are not cultivable usingstandard plating methods, we measured the proportion of marine lysogenicbacteria in natural communities by prophage induction. Mitomycin C, UVradiation, sunlight, temperature and pressure were used to induce prophage inlysogenic bacteria from estuarine, coastal and oligotrophic offshoreenvironments. To determine if hydrocarbon pollutants may cause the inductionof marine lysogens, aromatic and aliphatic hydrocarbons (including Bunker C 6fuel oil, phenanthrene, naphthalene, pyrene, and trichloroethylene) were alsoused as inducing agents. Induction was most often found in estuarineenvironments, where viral direct counts increased from 128.8 to 345% of theuninduced control, resulting in mortality of 10.5 to 67.3% (average 34%) ofthe bacterial population. Up to 38% of the bacterial population waslysogenized in estuarine environments, as calculated from an average burstsize. Microbial populations from oligotrophic offshore environments wereinducible at 3 of 11 stations sampled. Eight of the 11 samples (73%) treatedwith polyaromatic hydrocarbons resulted in prophage induction in naturalpopulations. Time series analysis was also conducted in 2 samples induced bymitomycin C from the Atlantic Ocean near the coast of North Carolina, USA.For both samples, significant decreases in bacterial numbers were detected intreated samples after 8 h of incubation. A significant increase of viruseswas detected at 8 h at one station and at 24 h at the other station afterinduction. This study indicates that natural lysogenic populations aresensitive to a variety of inducing agents, and induction occurs morefrequently in coastal and estuarine environments than offshore environments.