BACTERIOPHAGE DIVERSITY IN THE NORTH-SEA

In recent years interest in bacteriophages in aquatic environments has increased. Electron microscopy studies have revealed high numbers of phage particles (10(4) to 10(7) particles per mi) in the marine enviro nment. However, the ecological role of these bacteriophages is still u nknown, and the role of the phages in the control of bacterioplankton by lysis and the potential for gene transfer are disputed. Even the ba sic questions of the genetic relationships of the phages and the diver sity of phage-host systems in aquatic environments have not been answe red. We investigated the diversity of 22 phage-host systems after 85 p hages were collected at one station near a German island, Helgoland, l ocated in the North Sea. The relationships among the phages were deter mined by electron microscopy, DNA-DNA hybridization, and host range st udies. On the basis of morphology, 11 phages were assigned to the viru s family, Myoviridae, 7 phages were assigned to the family Siphovirida e, and 4 phages were assigned to the family Podoviridae, DNA-DNA hybri dization confirmed that there was no DNA homology between phages belon ging to different families. We found that the 22 marine bacteriophages belonged to 13 different species. The host bacteria were differentiat ed by morphological and physiological tests and by 16S ribosomal DNA s equencing. All of the bacteria were gram negative, facultatively anaer obic, motile, and coccoid, The 16S rRNA sequences of the bacteria exhi bited high levels of similarity (98 to 99%) with the sequences of orga nisms belonging to the genus Pseudoalteromonas, which belongs to the g amma subdivision of the class Proteobacteria.