Incorporation of viruses into the budget of microbial C-transfer A first approach

Abstract

Viral lysis of bacteria has been suggested to be a quantitatively important process in the removal of bacteria, and potentially also in the production of DOC, in the ocean. In order to investigate the quantitative role of viruses in the pelagic microbial ecosystem, a die1 study was undertaken, comprising measurements of particulate and dissolved primary production, bactenal production, bacterial grazing by flagellates, bacterial lysis by viruses, and production of viruses. Estimates of algal excretion (4.7 pm01 C 1-' d-I) and bacterial carbon consumption (3.0 pm01 C I-' d-l) were in reasonable balance. Predation (2.9 pm01 C 1-' d-l) exceeded bacterial production (1.5 pm01 C 1-' d-l) estimates by a factor of 2. Major difficulties in balancing the budget emerged however, from the estimates of vual lysis of bacteria (9.2 pm01 C I-' d-l), which exceeded bacterial production by a factor of 6. Despite these problems, results support the idea that viral lysis may b e a quantitatively significant process that needs to b e incorporated into budgets of microbial C-transfer.

Evaluation of incubation-based methods for estimating virioplankton production in estuaries

“…VP estimates over a depth gradient in the hyper-eutrophic and stratified freshwater lake Plußsee ranged from 0.2 × 10 10 to 1.9 × 10 10 viruses l -1 d -1 using the FVIC method (Weinbauer & Höfle 1998b). VP estimates based on measurements of viral decay ranged from 7 × 10 10 to 155 × 10 10 viruses l -1 d -1 in coastal Norwegian waters (Heldal & Bratbak 1991) and 17 × 10 10 viruses l -1 d -1 in the Bay of Århus, Denmark (Bratbak et al 1992). However, as the aggregate results of this study demonstrate, a meaningful comparison of reported VP rates between different marine environments is complicated by the inherent variability between methods.…”

“…In low productivity environments most BP is lost to grazing, while in more productive coastal and estuarine environments BP typically exceeds grazing (Strom 2000). Making a conclusion for the impact of viral lysis on BP across a range of aquatic environments is confounded by the inexplicable observation that viral lysis often consumes >100% of BP (Bratbak et al 1992, GuixaBoixereu et al 2002. For the VP rates reported here, 6 of the 14 FLV-based estimates showed >100% of BP consumed.…”

“…Estimating in situ VP has been addressed through a diverse group of methodologies, including indirect approaches such as viral decay or loss rates (Heldal & Bratbak 1991, Suttle & Chen 1992, Wommack et al 1996, calculated virus-host contact rates (Waterbury & Valois 1993, Suttle & Chan 1994, and determining the frequency of visibly infected cells (FVIC) using transmission electron microscopy (TEM) (Proctor & Fuhrman 1990, Bratbak et al 1992, Weinbauer et al 1993. Direct approaches to estimating VP rely on short-term incubation of water samples (ca.…”

Bridging the Gap between Knowing and Modeling Viruses in Marine Systems—An Upcoming Frontier

“…Viral lysis of bacteria has been thought to create a close loop in which bacterial carbon is cycled back to the bacterial population or respired, and nutrients are regenerated (Proctor and Fuhrman, 1991;Bratbak et al, 1992;Thingstad et al, 1993). Consequently, bacterial lysis diverts carbon and other biologically elements away from higher trophic levels or may simply delay their transportation toward them (Fuhrman, 1992), by keeping the dissolved nutrients within the so-called "viral loop" (Suttle and Chan, 1993).…”

Indirect interactions in the microbial world: specificities and similarities to plant–insect systems

“…Typically, bacterial abundance in the ocean is of the order of 10 6 -10 7 individuals/ml, and the relative abundance of viruses, bacteria, and heterotrophic nanoflagellates [(HNF), the dominant group of protozoan predators of bacteria] is 10:1:10 -3 (Noble and Fuhrman 1998;Tanaka and Rassoulzadegan 2002). This implies that frequent interactions occur between organic and inorganic substrates, bacteria, viruses, and protozoan predators, which act as strong trophic links connecting phytoplankton-derived organic resources to the higher trophic levels via heterotrophic bacteria, and form the basis for the important biogeochemical roles played by microbial food webs in aquatic systems (referred to as the microbial loop by Azam et al 1983, and the viral loop by Bratbak et al 1992). In addition, viral lysis and protozoan predation are two major sources of bacterial mortality (Fuhrman and Noble 1995;Fuhrman 1999;Strom 2000;Wommack and Colwell 2000), although their relative contribution to bacterial mortality may vary greatly among and within ecosystems (Weinbauer and Höfle 1998;Colombet et al 2006;Lymer et al 2008) or seasons (Jacquet et al 2005;Pradeep Ram et al 2005).…”