International Polar Year 2007–2008 - WMO

Biological and chemical analyses of the newly obtained
accretion ice core and the development of
clean procedures for biological sampling continued in
collaboration with French scientists from Laboratoire
de Glaciologie et Géophysique de l’Environnement,
Laboratoire de Ecologie Microbienne аnd Laboratoire
de Microbiologie des Environnements Extrêmes in the
bilateral research network “Vostok,” established just
prior to IPY. A special effort was made by biologists
from the Petersburg Nuclear Physics Institute (PNPI)
of the Russian Academy of Sciences to accurately assess
the cell concentration of microorganisms in the
Antarctic ice sheet in the vicinity of Vostok Station.
Segments of the Vostok ice core and 10 kg samples of
snow collected from layers deposited before the beginning
of human activity in the area were collected
avoiding contamination (Figs. 2.6-5). The samples
were then processed using state-of-the-art decontamination
procedures (Bulat et al., 2004, 2007; Alekhina et
al., 2007) and concentrated up to 3000-10,000 times.
Among methods used for detection and counting of
microbial cells (fluorescence, laser confocal and scanning
electron microscopy, cytofluorimetry) only the
flow cytofluorimetry was successful in assessing the
very low quantities of cells typical in the samples studied.
The results suggest extremely low biomass in ice
strata, both of atmospheric and lake water origins, and
emphasize the importance of ultra-clean procedures
(and decontamination where necessary) if ice samples
are to be used for microbiological analyses (Bulat et
al., 2009). Similar pre-IPY studies were undertaken by
U.S. and U.K. researchers, confirming low cell numbers
and diversity in glacial and accreted ice, though their
findings suggested higher cell numbers and diversity
in the accreted ice (Christner et al., 2006).
The data obtained for contemporary snow and glacial
(meteoric) ice suggest that the Antarctic ice sheet
over Lake Vostok serves as a barrier preventing the
contact of potential lake biota with the surface rather
than being a conveyer of dormant microorganisms
inoculating the lake water as assumed in the earliest
studies. The purity of accreted lake ice suggest that
Lake Vostok water may have a very low microbial
content as PCR-based prokaryotic 16S ribosomal RNA
gene sequencing has indicated that accretion ice is
essentially free of bacterial and archaeal DNA (Bulat
et al., 2009). The few bacterial phylotypes recovered
from accreted ice cores have all been found in those
Fig. 2.6-4. Spatial
and temporal
coverage of the lake
ice extracted as a
core from the deep
borehole at Vostok
Station (adapted
from Ekaykin et
al., 2010). The Inset
shows a relatively
large inclusion of
Lake Vostok bottom
sedimentthat was
trapped in lake
ice 1 as the glacier
was crossing the
“islet” located 40
km upstream of the
borehole.
s C I e n C e P r o g r a m 249