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Baltic flora of bacterial plankton mapped out

Published Jun 23, 2011

Using advanced DNA sequencing technology, researchers at KTH in an international research collaboration have created a three dimensional map of the distribution of thousands of bacterial plankton species in the Baltic Sea. Since bacteria play key roles in various nutrient cycles in the marine environment, this is important work in order to understand how the Baltic Sea’s ecosystem functions.

The bacteriological survey shows that salinity has a major influence on the species composition of bacteria in the Baltic Sea. West of the Danish Straits, typical marine species dominate but the further into the Baltic Sea you go, the bacterial community starts to contain bacteria that are close relatives of sea-leaving species.

The type of bacteria also changes drastically when you get down to the oxygen-free depths. Here organisms that can use other molecules than oxygen for respiration dominate.

This is the first step in creating an overall picture of the Baltic Sea’s microbial world. The aim in the long term is to determine which biogeochemical processes that are carried out by the various microorganisms, and how these processes are controlled.

“Now we have a map of the type of bacteria there are, at least during the summer. The next step will be to determine which metabolic properties the microorganisms have in different areas and at different depths, says KTH researcher Anders Andersson, who works with systems biology studies of microbial communities, and who directed the study.

Scientists have sequenced the bacterial DNA from a few hundred samples taken at various locations and depths throughout the entire Baltic Sea including the Kattegat and Skagerrak; the samples were collected during an expedition coordinated by the Liebniz Institute for Baltic Studies in Rostock.

By sequencing the taxonomic marker genes from thousands of bacteria in each sample, the researchers have created a clear picture of the bacterial species present and at what frequencies. The DNA sequencing method is based on so-called pyrosequencing, which was originally developed by KTH researcher Pål Nyrén. The method uses a more modern version of pyrosequencing, which can read approximately one million sequences simultaneously.

“The new sequencing technologies have revolutionized not only organism biology and medical research, but also ecology. Now you can get a detailed picture of which micro organisms can be found in different environments and begin to create models as to what determines the composition and dynamics of microorganisms,” says Anders Andersson.

The study has attracted international attention and was recently published online in Nature Publishing Group’s journal ISME Journal.

For more information, contact Anders Andersson on 08-515 26 00 or

Here is the article on Nature's website

Peter Larsson