Viral mortality of the marine alga Emiliania huxleyi (Haptophyceae) and termination of algal blooms

Abstract

The possible roles of viruses in phytoplankton dynamics were investigated in seawater mesocosms with natural assemblages of phytoplankton growing under various nutrient regimes. Blooms of the marine coccolithophorid Emiliania huxleyi (Lohmann) Hay & Mohler were in some cases succeeded by an increase in the abundance of a morphologically homogeneous population of viruses. The viruses had an hexagonal outline and were about 180 nm in diameter. Similar viruses were found both intracellularly and associated with apparently lysed cells. Viral lysis could account for 25 to 100 % of the net mortality of E huxleyi when the blooms declined under non-limiting nutrient conditions or when the nitrate concentration was low. Production of viruses was limited when the phosphate concentration was low. Dur~ng a bloom of E. huxleyi in Norwegian coastal waters in 1990 we found that the concentration of free algal viruses was increasing at the end of the bloom, indicating that viruses of E. huxleyi may be important under natural conditions as well. These results suggest that viral mortality of phytoplankton may be an important factor regulating community structure, diversity and biomass production in marine environments.

Seasonal Variation of Virioplankton in a Eutrophic Shallow Lake

“…It is suggested that high concentrations of phytoplankton might result in more planktonic viruses, and the significant correlation has been suggested by some previous studies (Boehme et al, 1993;Maranger & Bird, 1995;Weinbauer et al, 1995). In addition, phytoplankton had larger burst sizes than bacterioplankton, ranging from 92 to 500 (Bratbak et al, 1993;Suttle & Chan, 1994). In a previous study, we have found that there are large numbers of virus particles existing in algae tubule (Liu et al, 2005).…”

Isolation of viruses responsible for the demise of an Emiliania huxleyi bloom in the English Channel

“…Although such conclusions from similar data sets are not new (Bratbak et al, 1993Brussaard et al, 1996;Castberg et al, 2001), there have been no reports of E. huxleyi-speci¢c viruses being isolated and maintained in culture from E. huxleyi blooms. Bratbak et al (1996) reported the initial isolation of a virus by plaque assay, however they were unable to propagate it further for characterization.…”

“…This further supports the prediction made by Wilson et al (in press) who discussed that viruses would play a much more important role towards the end of a bloom when virus concentrations would reach a threshold level required to cause termination of that bloom. Indeed, numerous mesocosm studies have been conducted where high concentrations of LVLPs have been observed following the demise of the E. huxleyi population (Bratbak et al, 1993;Castberg et al, 2001). It is di¤cult to measure such termination at sea since it is not often logistically possible to be on a ship throughout the progression of a bloom.…”

Pilot study of an EST approach of the coccolithophorid Emiliania huxleyi during a virus infection

“…Several studies have investigated the role of viruses in controlling the bloom development of E. huxleyi (Bratbak et al, 1993, Brussaard et al, 1996, Castberg et al, 2001, Jaquet et al, 2002, Wilson et al, 1998, 2002a, 2002b. It became evident from these investigations that viruses are intrinsically linked to the decline of E. huxleyi blooms.…”