never quenched the curiosity they evoke, so research goes on.
Phytoplankton Viruses
(^) More than 50 species of phytoplankton have been shown to contain viruses or virus-
like particles, and it is likely that viruses infect every major algal division (Munn
2006). Many of these viruses have now been characterized (Lawrence 2008), and they
may play a major role in controlling the size and duration of phytoplankton blooms.
This was well illustrated for E. huxleyi in mesocosms (1 m^3 containers) (Martinez et
al. 2007) where a bloom was followed by a rapid increase in virus particles. Exposure
of the vegetative (coccolith-bearing diploid) stage to the virus induces the sexual stage
of the life cycle (Frada et al. 2008). The haploid sexual stage of the coccolithophore is
immune to the virus, thus allowing the population an escape mechanism.
(^) Five viruses infecting diatom species have been studied, and these replicate either in
the cytoplasm or in the nucleus. Eissler et al. (2009) studied the lytic cycle of an
intranuclear virus infecting the diatom Chaetoceros wighamii. Following inoculation
of cultures with the virus, rod-like arrays appear within the nucleus during the early
stage of infection (Fig. 2.15).
Fig. 2.15 Transmission electron micrographs of Chaetoceros cf. wighamii. (a) Section
of a healthy nucleus: NU – nucleus, NS – nucleolus, CH – choroplast). (b) Section of
a cell at early infection, showing rod-like arrays (RLA) and rod-like arrays in cross-
section (CSRLA), including an insert for more detail (scale bar, 50 nm). (c) Thin
section of a cell at mid-infection, showing virus-like particles (VLP), RLA, and
CSRLA. (d) Thin section of a cell at late infection, showing VLP, including an insert
for more detail (scale bar, 50 nm).
(^) (After Eissler et al. 2009, with permission from the Journal of Phycology.)