8/6/2019 Timeline of the ancient mariners

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Changes in the composition ofancient planktonic communities

can be studied by microscopic andchemical analyses of sedimentsand are usually explained by changes

in environmental conditions.However, the viral populations thatare associated with these communi

ties, and their roles during thesechanges, are poorly understood.Writing in Science, Marco Coolen

now provides a 7,000year recordof the population dynamics ofthe photosynthetic haptophyte

alga Emiliania huxleyi and itsviruses in the Black Sea.

The author PCR

amplified and sequencedDNA fragmentsencoding parts of the

major capsid protein(MCP) andphosphoglycerate

mutase (PGM) ofE. huxleyiinfectingcoccolithoviruses

from sedimentsof the westernBlack Sea that had

been deposited between 7,500 and450 years ago. He found a total of

33 viral genotypes and studied theircooccurrence with 11 E. huxleyigenotypes that had been previously

identified by sequencing DNAencoding mitochondrial cytochromeoxidase subunit I (COI) from the

same sediment samples. DNAfragments were wellpreserved in the sedi

ment record, as shown bya constant ratio betweenCOIgene copy numbers

and the concentrationofE. huxleyispecificrecalcitrant lipid bio

markers. Most shifts inviral and host populations coincided with

important environmental changes thataffected salinity

and nutrient availability, as previously

determined by

geochemical andpalynological

studies. Whereas

some host and viral genotypesseemed to show limited persistence,

others coexisted for long periods oftime. For example, the host genotype COI1 and the viral genotype

MCP20PGM2 coexisted for morethan a century (495640 years ago).

Similar methods could be applied

to other photosynthetic marinemicroorganisms such as cyanobacteria, which are infected by their

own DNA viruses. Given the majorrole of phytoplankton in the globalcarbon cycle, an understanding of

the importance of viruses in controlling past and present phytoplanktonpopulations is greatly needed.

Furthermore, these studies may beuseful to paleoecologists and paleoclimatologists for improving their

interpretation of past climate records.Cesar Sanchez

EVOLUTION

Timeline of the ancient mariners

a 7,000year

record of thepopulation

dynamics of

Emiliania huxleyi

and its viruses

ORIGINAL RESEARCH PAPER Coolen, M. J. L.

7000 years ofEmiliania huxleyi viruses in the Black

Sea. Science333, 451452 (2011)

FURTHER READING Suttle, C. A. Marine viruses

major players in the global ecosystem.Nature

Rev. Microbiol.5, 801812 (2007)

R E S E A R C H H I G H L I G H T S

NATURE REVIEWS |MICROBIOLOGY VOLUME 9 | SEPTEMBER 2011

2011 Macmillan Publishers Limited. All rights reserved