Functional consequences of viral impacts on bacterial communities: a food-web model analysis

1. Viruses in aquatic ecosystems can alter the abundance of bacteria and influence organic matter flows and bacterial community composition, but the combined effects of the multiple processes involved in the bacteria-mediated carbon cycle are not entirely clear. 2. We developed a new conceptual model that incorporates a fundamental but neglected aspect of bacteria-organic matter interactions: that different bacterial groups utilize different kinds of organic matter. In addition, the model incorporates several other realistic features of microbial food webs, including the presence of lysogenic viruses, bacterial resistance to viral infection and dependence of protozoan grazing rate on viral infection. 3. Our model analysis indicates that a 'viral shunt' view (i.e. viruses enhance bacterial utilization of organic carbon through regeneration of organic matter but diminish carbon flow to higher trophic levels) is robust, regardless of the specific situations we examined by either incorporating or ignoring various features of microbial food webs. 4. We also found that host-specific mortality induced by viral infection changes the bacterial utilization of different types of organic matter, which was attributable to diminished 'apparent competition' between predator-sharing bacterial groups that use different carbon sources. This mechanism can facilitate transformation to carbon dioxide of diverse types of carbon sources (e.g. organic matter of algal and terrestrial origin, methane or xenobiotics) and extends the previously recognized roles of viruses in microbial food webs.