AME 51:195-208 (2008)  -  DOI: https://doi.org/10.3354/ame01190

ABSTRACT: Viruses are the most abundant biological entities in aquatic ecosystems, and heterotrophic bacteria form the major host reservoir for these viruses. Together with small protozoan grazers, these biological compartments are now recognized as the most abundant microorganisms on earth. Bacterial loss, which constitutes a key process in pelagic ecosystems, is mainly a result of lysis by viruses and grazing by protists, which may be comparable at times. Both viruses and protozoan grazers are known to be driving forces in shaping bacterial diversity. A significant correlation between viruses and protozoan grazers has been reported in various ecosystems. Some studies have also shown that grazers can feed directly on viruses, although the transfer of carbon to the higher trophic levels via this process seems to be of minor importance. Thus, there are many routes of interaction between grazers, bacteria and viruses in pelagic systems, but few studies have attempted to characterize them. Interestingly, experimental studies have recently revealed both direct and indirect control by viruses and protozoan grazers on bacteria. Interactions between bacteria, between viruses and between heterotrophic flagellates are also likely to occur. From a mathematical point of view, we can argue that there are 9 different possible pathways. Although some of these have been well documented, others have barely been mentioned. This review attempts to cover advances in the field in recent years and concentrates on addressing the underexplored interactions among viruses, bacteria and heterotrophic nanoflagellates.

KEY WORDS: Viruses · Bacteria · Protists · Interactions · Aquatic ecosystems