Marine mystery solved: 'Rare' bacteria in the ocean ain't necessarily so

July 21, 2011 by Tracey Bryant, University of Delaware
Barbara Campbell, assistant professor of marine biosciences, led a study that sheds light on the ocean's 'rare biosphere' of bacterial life.

( -- A teaspoon of seawater contains thousands of naturally occurring bacteria. Scientists previously believed that less than half of these ocean microbes are actively taking up organic compounds, while the remainder -- a mix of rare species -- lie dormant.

Not so, according to researchers from the University of Delaware and the University of Southern California. In a study reported in the July 18 online edition of the , the UD-USC team found that over half the sampled from surface waters actively cycled between abundant and rare, and only about 12 percent always remained rare and potentially inactive.

“Scientists have been interested in shedding light on this so-called ‘rare biosphere’ made up of a huge diversity of ,” says Barbara Campbell, assistant professor of marine biosciences in UD’s College of Earth, Ocean, and Environment. “The surprise is that many of these bacteria are actually quite active, and they cycle from low to great abundance.”

Campbell’s co-authors on the study include David Kirchman, Maxwell P. and Mildred H. Harrington Professor of Marine Biosciences at UD, and John Heidelberg, associate professor of biological sciences at USC.

Every month for three years, Campbell and colleagues collected water samples from a site in the Atlantic Ocean near UD’s Hugh R. Sharp Campus in Lewes, Del. Then using a high-throughput sequencing technique at USC, the researchers examined a portion of the genome of individual microbial species -- the ribosomal RNA -- a gene involved in enzyme production. The more copies of RNA present, the more metabolically active the cell. The team analyzed over 500,000 sequences.

For the first time, Campbell says, the team saw some of the bacteria switch from being rare to abundant. Their findings also suggest that although abundance follows activity in the majority of species, a significant portion of the rare community is active, some with growth rates that decrease as abundance increases.

“Many of these bacteria cycle between abundant and rare, and there’s a reason for that,” Campbell notes. “Bacteria that lie dormant appear to serve as seeds for the future community -- like a microbial seed bank.”

The scientists are now trying to explain what causes the cells to become dormant and active again. It doesn’t appear to be seasonally driven or to correlate much with the environment, but it may be driven by the microbial community itself, Campbell explains.

“When one bacteria is happy, it’s in association with its cousins in a community. You might say it likes it neighborhood,” Campbell says.

Better understanding the microbial world matters, Campbell points out, since these tiny organisms not only provide food for other organisms, but also affect the cycling of carbon, nitrogen and sulfur throughout the ocean and across the entire planet, with important implications for climate change and other phenomena.

She also notes that the molecular methods used in the research may be applied to other problems, such as determining at your local beach if the bacteria that affect water quality are alive and replicating.

Explore further: How bacteria keep us healthy

More information: … /1101405108.abstract

Related Stories

How bacteria keep us healthy

January 25, 2011

( -- Joerg Graf is studying medicinal leeches for clues about how changes in diet affect microorganisms in the digestive tract.

Every Microbe in Its Place

August 29, 2006

Marine bacteria populations vary according to ocean conditions, say University of Southern California and Columbia University marine biologists. The finding could improve reach and accuracy of ocean-change models.

Researchers trace source of cocaine-driven TB outbreak

February 23, 2011

( -- Simon Fraser University researchers are the first to combine the latest techniques of whole bacterial genome analysis with social networking surveys to track down the puzzling origins of a tuberculosis (TB) ...

Recommended for you

Tasmanian tiger just another marsupial in the pouch

February 21, 2018

Australia's ill-fated Tasmanian tiger looked like any other marsupial when born but assumed dog-like features by the time it left the mother's pouch, scientists said Wednesday in shedding new light on its puzzling evolution.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.