Biology Reference
In-Depth Information
However, the applicability of these investigations to the peculiar character-
istics of the polar microbiota is largely unknown. Deeper understanding is
necessary in light of the important role that polar waters play in global carbon
cycling. The microbial component represents up to 90% of cellular DNA
(
Paul, Jeffrey, & DeFlaun, 1985
) and is estimated to be responsible for up
to 80% of the primary carbon production (
Douglas, 1984; Ducklow,
1999; Li et al., 1983
) and for most of the carbon flux between the sea water
and the atmosphere (
Azam, 1998; Azam & Malfatti, 2007
).
Environmental genomics revealed that heterotrophic bacteria play a key
role in controlling carbon fluxes within oceans. These bacteria dominate
biogeochemical cycles and are part of the microbial loop which, at least
in part, causes the response of oceanic ecosystems to climate change
(
Kirchman et al., 2009
). Recent diversity studies that employed sequencing
of ribosomal RNA genes (
Galand, Casamayor, Kirchman, & Lovejoy, 2009;
Ghiglione & Murray, 2012; Kirchman, Cottrell, & Lovejoy, 2010
), and
metagenomics and metaproteomics (
Grzymski et al., 2012; Wilkins et al.,
2013; Williams et al., 2012, 2013
) have clarified some of the aspects of
the interactions between microorganisms and the polar environment, which
is unique in terms of environmental parameters such as temperature, day
length and trophic interactions.
Antarctic marine waters harbour taxa of heterotrophic microbes similar
to those found in temperate and tropical waters. Among these, the most
dominant are
a
-Proteobacteria and, in particular, specific phylotypes of
SAR11 (
Brown et al., 2012
),
g
-Proteobacteria, Flavobacteria and
ammonia-oxidising Marine Group I Crenarchaeota (
Grzymski et al.,
2012; Wilkins et al., 2013; Williams et al., 2012
). However, the emerging
view is that, while the taxa present might be distributed worldwide, there are
clear signatures of allopatric speciation, which are only evident at a finer
phylogenetic scale (
Brown et al., 2012
).
The geographic separation necessary for such evolutionary events is pro-
vided by sharp transitions in chemicophysical parameters that mark and iso-
late water masses (
Agogu
ยด
, Lamy, Neal, Sogin, & Herndl, 2011
). The
Antarctic Polar Front provides one of the most dramatic examples of such
transitions. Here, the water drops
3
C in temperature over a space of less
than 30 miles which results in abrupt shifts in the microbial community
composition and functional gene distribution (
Wilkins et al., 2013
).
Moreover, certain taxa become transiently dominant in response to par-
ticular seasonal changes in environmental parameters such as the Marine
Group I Crenarchaeota which show a dramatic increase in relative
