Fact box 3. The role of ocean viruses and bacteria in the carbon cycle
Free living marine microorganisms (plankton, bacteria and vi- day from the biological pool within the oceans (Suttle, 2007). It is
ruses) are hardly visible to the human eye, but account for up to thought that up to 25% of all living carbon in the oceans is made
90% of living biomass in the sea (Sogin et al., 2006; Suttle, 2007). available through the action of viruses (Hoyle and Robinson, 2003).
These microscopic factories are responsible for >95% of primary
production in oceans, producing and respiring a major part of the There is still a critical question as to whether viruses hinder or
reduced carbon or organic matter (Pomeroy et al., 2007). stimulate biological production (Gobler et al., 1997). There is an
ongoing debate whether viruses (1) shortcircuit the biological
Plankton pump by releasing elements back to the dissolved phase (Poor-
More than 36.5Gt of CO
2
is captured each year by planktonic vin et al., 2004), (2) prime the biological pump by accelerating
algae through photosynthesis in the oceans (Gonzalez, et al. host export from the euphotic zone (Lawrence and Suttle, 2004)
(2008). Zooplankton dynamics are a major controlling factor in or (3) drive particle aggregation and transfer of carbon into the
the sedimentation of particulate carbon in open oceans (Bishop deep sea through the release of sticky colloidal cellular compo-
and Wood, 2009). Of the captured CO
2
, and an estimated 0.5Gt nents during viral lysis (Mari et al., 2005).
C yr
–1
is stored at the sea bed (Seiter et al., 2005).
Bacteria
Marine viruses and bacteria – significant in the carbon budget Ocean bacteria are capable of taking up CO
2
with the help of
Marine viruses require other organic life to exist, but in them- sunlight and a unique light-capturing pigment, proteorhodopsin,
selves have a biomass equivalent to 75 million blue whales which was first discovered in 2000 (Beja et al., 2001). Proteorho-
(11.25Gt). The estimated 1x1030 viruses in the ocean, if stretched dopsin can be found in nearly half of the sea bacteria. Knowledge
end to end, would span farther than the nearest 60 galaxies (Sut- of marine bacteria may come to be of major importance to our
tle, 2007). Although the story of marine viruses is still emerging, understanding of what the climate impact of rising CO
2
emis-
it is becoming increasingly clear that we need to incorporate vi- sions means for the oceans.
ruses and virus-mediated processes into our understanding of
ocean biology and biogeochemistry (Suttle, 2007). Life deep below the sea bed
Life has been shown to exist in the deep biosphere, even 800m
Interactions between viruses and their hosts impact several impor- below the sea floor. It is estimated that 90 Gt of microbial organ-
tant biological processes in the world’s oceans including biogeo- isms (in terms of carbon mass) are living in the sediments and
chemical cycling. They can control carbon cycling due to cell lysis rocks of the sea bed, with bacteria dominating the top 10 cm, but
and microbial diversity (by selecting for various hosts) (Wiggington, more than 87% made up by a group of single cell microorganisms
2008). Every second, approximately 1x1023 viral infections occur in known as Archaea. It is still not clear what their ecological func-
the ocean and cause infection of 20–40% surface water prokaryotes tions are, or even how they survive in such a low flux environment,
every day resulting in the release of 108–109 tonnes of carbon per living on previously digested fossil remains (Lipp et al., 2008).
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