Marine cyanophages infecting oceanic and coastal strains of Synechococcus: abundance, morphology, cross-infectivity and growth characteristics

Abstract

Eight different phycoerythrin-and phycocyanin-containing strains of Synechococcus spp. and 1 strain of Anacystis marina were screened against 29 natural virus communities taken from 3 locations in south Texas (USA) coastal waters, at different times of the year. In add~tion, 1 sample was screened from Peconic Bay, New York, USA. Cyanophages were detected in all samples, but the frequency with which they were detected and their abundance depended upon the strain of Synechococcus sp. that was screened. Viruses that infected red Synechococcus spp. strains (DC2, SYN 48) were particularly common and in some instances were in excess of 105 ml-l The abundances of cyanophages were weakly correlated with temperature (r2= 0.53 to 0.70), although they occurred at all of the temperatures (12 to 30.4 "C) and salinities (18 to 70 ppt) that were screened. The 7 cyanophages that were cloned belonged to the same 3 families of viruses that have been observed to infect freshwater cyanobacteria, namely the Siphoviridae (formerly Styloviridae), Myoviridae and Podoviridae. The cyanophage clones varied in host-specificity. For example, 1 clone infected a single Synechococcus sp. strain of 12 that were tested, whereas, another infected 4 of 9 strains tested. Growth characteristics of 1 of the virus clones was determined for a single host (BCCI). Photosynthesis in BCCI was not affected until near the onset of cell lysis and the virus burst cycle was complete ca 17 h post-infection. The burst size was approximately 250 infective particles. The high abundance of cyanophages in the natural environment provides further evidence that viruses are probably important regulators of phytoplankton dynamics in marine systems.

Re-examination of the relationship between marine virus and microbial cell abundances

“…For example, if prokaryote and virus abundances varied systematically with another environmental co-factor during a transect, then this would potentially influence the inferred relationship between virus and prokaryote abundances. In that same way, variation in environmental correlates, including temperature and incident ration, may directly modify virus life history traits [20,44]. Likewise, some of the marine survey datasets examined here constitute repeated measurements at the same location (e.g., at the Bermuda Atlantic Time-series Study (BATS)).…”

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

“…Different approaches, relying on conceptual models or other indirect measurements, suggested that losses from viral lysis were in the same range as those attributed to protist grazing (Proctor and Fuhrman, 1990;Suttle and Chan, 1993). For a mesocosms experiment, for example, Fuhrman and Noble (1995) showed that viruses and protists were responsible for similar amounts of bacterial loss (they specifically account for 70-75% of the total apparent mortality with these two mechanisms).…”

“…The "viral loop" was not considered as an independent process, but rather as a component of the "microbial loop, " and early estimates suggested that as much as 25% of the primary production in the ocean flows through this loop (Wilhelm and Suttle, 1999). For its capacity to disrupt the microbial loop, it was even advanced that the viral loop leads to a "futile cycle" or "short circuit" of carbon flow, resulting in an energy loss by respiration as the cycle turns (Suttle and Chan, 1993;Azam et al, 1994), since bacteria do not convert DOM into biomass with a 100% efficiency.…”

“…Phytoplankton is inevitably exposed to high physiological stress in dense blooms which increases cell lysis (Brussaard et al, 1997), where lytic viruses play a significant role by completely destroying host populations within hours to days (Suttle and Chan, 1993;Cottrell and Suttle, 1995;Jacobsen et al, 1996;Bratbak et al, 1998a;Baudoux and Brussaard, 2005). As with viral infection in bacteria, P limitation seems to play an important role in viruses-phytoplankton interactions.…”

“…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). This semi-closed trophic loop (Figure 2), fed externally by the release of DOM from phytoplankton and grazers, has the net effect of oxidizing organic matter and regenerating inorganic nutrients (Proctor and Fuhrman, 1991).Viral lysis of bacterial and phytoplankton cells removes a portion of autotrophic and microbial heterotrophic production from protozoan grazers providing, at the same time, a short circuit to the "traditional" concept of carbon cycling.…”