OCCURRENCE OF LYSOGENIC BACTERIA IN MARINE MICROBIAL COMMUNITIES AS DETERMINED BY PROPHAGE INDUCTION

Viruses are abundant and dynamic members of the marine microbial commu nity, and it is important to understand their role in the ecology of n atural microbial populations. We have previously found lysogenic bacte ria to be a significant proportion (43%) of the cultivable heterotroph ic microbial population. As the majority of marine bacteria are not cu ltivable using standard plating methods, we measured the proportion of marine lysogenic bacteria in natural communities by prophage inductio n. Mitomycin C, UV radiation, sunlight, temperature and pressure were used to induce prophage in lysogenic bacteria from estuarine, coastal and oligotrophic offshore environments. To determine if hydrocarbon po llutants may cause the induction of marine lysogens, aromatic and alip hatic hydrocarbons (including Bunker C #6 fuel oil, phenanthrene, naph thalene, pyrene, and trichloroethylene) were also used as inducing age nts. Induction was most often found in estuarine environments, where v iral direct counts increased from 128.8 to 345% of the uninduced contr ol, resulting in mortality of 10.5 to 67.3% (average 34%) of the bacte rial population. Up to 38% of the bacterial population was lysogenized in estuarine environments, as calculated from an average burst size. Microbial populations from oligotrophic offshore environments were ind ucible at 3 of 11 stations sampled. Eight of the 11 samples (73%) trea ted with polyaromatic hydrocarbons resulted in prophage induction in n atural populations. Time series analysis was also conducted in 2 sampl es induced by mitomycin C from the Atlantic Ocean near the coast of No rth Carolina, USA. For both samples, significant decreases in bacteria l numbers were detected in treated samples after 8 h of incubation. A significant increase of viruses was detected at 8 h at one station and at 24 h at the other station after induction. This study indicates th at natural lysogenic populations are sensitive to a variety of inducin g agents, and induction occurs more frequently in coastal and estuarin e environments than offshore environments.