Identical virus, host populations can prevail for centuries, WHOI researcher reports

July 21, 2011

A Woods Hole Oceanographic Institution (WHOI) scientist, analyzing ancient plankton DNA signatures in sediments of the Black Sea, has found for the first time that the same genetic populations of a virus and its algal host can persist and coexist for centuries. The findings have implications for the ecological significance of viruses in shaping algae ecosystems in the ocean, and perhaps fresh water as well.

"The finding that the DNA of viruses and algal host cells can be preserved in the geological records is of great interest to microbial ecologists," said Marco Coolen of WHOI's Marine Chemistry and Geochemistry department and author of the study, which appears in the July 22 issue of Science. "This offers unprecedented insights into long-term algal, viral, and host population dynamics between globally important algae and their viral pathogens in the ocean."

In examining the 7,000-year continuous genetic record in sediments underlying the Black Sea, Coolen discovered that the DNA of both the Coccolithovirus and its host, Emiliania huxleyi, a phytoplankton that plays a major role in the global carbon cycle, have been preserved over thousands of years.

"Biologists now for the first time have a picture of long-term viral/host dynamics in the ocean," Coolen said. Previous laboratory work had confirmed such co-existence for only a few successive years.

Coolen added that much longer virus/host records such as the ones he studied, for the first time "could answer important questions, such as:

'What factors are involved in controlling viral infection of the globally important marine algae and how long can the same host and virus populations co-exist?' and 'Were past algal populations only controlled by the prevailing environmental conditions or did viruses also play an important role in shaping past algal community structures?'"

The latter question is of particular interest, Coolen said, because "nobody has long-term records of viruses. Ecological shifts in past algal communities are generally explained by changes in climate and environmental conditions." Now it seems possible, he said, that viruses also played an important role in shaping past algal communities.

This is important for E. huxleyi, which performs photosynthesis--"just like plants," says WHOI scientist Benjamin Van Mooy. "They consume carbon dioxide." In doing so, they reduce the amount of CO2 released into the atmosphere. They form a calcium carbonate shell, also helping to regulate the carbon cycle.

But DNA viruses of the genus Coccolithovirus kill off large populations of E. huxleyi, particularly in the North Atlantic. Van Mooy has traced this phenomenon to lipids, or fatty compounds, in certain viruses. If viruses are killing off phytoplankton, this can increase greenhouse emissions, Van Mooy suggests. "That's important because if viruses infect a whole bunch of cells, then they can't perform photosynthesis, they can't take up carbon dioxide."

Coolen says his data buttress Van Mooy's work by suggesting a significant role for viruses in affecting the algal population and carbon cycling in the past. He observed, for example, major shifts in the types of Coccolithovirus and E. huxleyi in the Black Sea sediments over the centuries. Environmental conditions almost certainly had a role in selecting successful E. huxleyi genotypes, but Coolen believes viruses may have as well.

"Until now, shifts in past plankton species identified through the microscopic analysis of preserved diagnostic cellular fossils have mainly been linked to changes in environmental conditions and climate," Coolen said. "However, understanding the viral role in controlling past algal stocks is necessary to improve the interpretation of past climate records. This can now be studied using ancient DNA methods."

One thing that enabled Coolen to study sediments so far back in time was the continuous absence of oxygen in the bottom waters of the Black Sea the last 7,500 years. "This lack of oxygen facilitated the preservation of organic material in general and ancient viral and algal plankton DNA in particular," he said.

In addition, unpublished data from Coolen's lab "show that Black Sea sediments older than 7,500 years contain well-preserved DNA of a different suite of algae adapted to lower salinities and freshwater environments and likely also DNA of their viral pathogens," he said. "In other words, comparable studies could most likely be employed in a wide variety of marine and lake ecosystems.

"In a different and broader context," he adds, "it will perhaps be possible to reconstruct the historical spread of human viral diseases since a variety of human viral infections are also caused by DNA viruses."
-end-
The research was funded by grants from the National Science Foundation (NSF) and a grant from the Andrew W. Mellon Foundation.

The Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment.

Woods Hole Oceanographic Institution

Related DNA Articles from Brightsurf:

A new twist on DNA origami
A team* of scientists from ASU and Shanghai Jiao Tong University (SJTU) led by Hao Yan, ASU's Milton Glick Professor in the School of Molecular Sciences, and director of the ASU Biodesign Institute's Center for Molecular Design and Biomimetics, has just announced the creation of a new type of meta-DNA structures that will open up the fields of optoelectronics (including information storage and encryption) as well as synthetic biology.

Solving a DNA mystery
''A watched pot never boils,'' as the saying goes, but that was not the case for UC Santa Barbara researchers watching a ''pot'' of liquids formed from DNA.

Junk DNA might be really, really useful for biocomputing
When you don't understand how things work, it's not unusual to think of them as just plain old junk.

Designing DNA from scratch: Engineering the functions of micrometer-sized DNA droplets
Scientists at Tokyo Institute of Technology (Tokyo Tech) have constructed ''DNA droplets'' comprising designed DNA nanostructures.

Does DNA in the water tell us how many fish are there?
Researchers have developed a new non-invasive method to count individual fish by measuring the concentration of environmental DNA in the water, which could be applied for quantitative monitoring of aquatic ecosystems.

Zigzag DNA
How the cell organizes DNA into tightly packed chromosomes. Nature publication by Delft University of Technology and EMBL Heidelberg.

Scientists now know what DNA's chaperone looks like
Researchers have discovered the structure of the FACT protein -- a mysterious protein central to the functioning of DNA.

DNA is like everything else: it's not what you have, but how you use it
A new paradigm for reading out genetic information in DNA is described by Dr.

A new spin on DNA
For decades, researchers have chased ways to study biological machines.

From face to DNA: New method aims to improve match between DNA sample and face database
Predicting what someone's face looks like based on a DNA sample remains a hard nut to crack for science.

Read More: DNA News and DNA Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.