Researchers Find Unexpected Role For Marine Bacteria in the Chemistry of the Ocean

East Boothbay, Maine - New research published in the journal Nature Geosciences on 18 November 2012 suggests that cyanobacteria -- tiny photosynthetic bacteria -- living in vast open expanses of “blue ocean” waters may be playing a wholly unexpected role in determining ocean chemistry.

The study, led by Dr. Stephen Baines of the Department of Ecology and Evolution at Stony Brook University and Dr. Benjamin Twining of the Bigelow Laboratory for Ocean Sciences, used state-of-the-art high-resolution x-ray fluorescence microscopy to measure the elemental composition of single cells of photosynthetic bacteria collected from remote regions of the Pacific and Atlantic Oceans.

 “Surprisingly, the measurements revealed that cells of the genus Synechococcus accumulated substantial amounts of silicon, an element not previously thought to be of biological importance to this group of organisms,” said Baines.



The results of the study were confirmed in laboratory experiments conducted by the lead authors and their colleagues Drs. Mark Brzezinski and Jeff Krauss at the University of California at Santa Barbara.

“Silicon is important as a required element for diatoms, a group of unicellular algae that account for 20% of the photosynthesis on earth,” said Twining.  “Diatoms use the silicon to construct exquisite glass walls that also cause them to sink rapidly to the deep ocean. Because they take organic carbon with them when they sink, concentrations of carbon dioxide in the atmosphere—and indeed the global climate itself—are tied to the growth and sinking of diatoms in the ocean, which is tied to the availability of silicon.”

The open ocean was thought to be a nutrient-starved desert for most of the 20th century, but as observational techniques improved over the last few decades, scientists have discovered that these regions are actually occupied by a myriad of photosynthetic bacteria, specifically adapted to live there.  Added up over the whole ocean, these organisms also account for up to 20% of the photosynthesis on the planet.

The new study, “Significant silicon accumulation by marine picocyanobacteria,” suggests that the concentration of silicon in cyanobacteria cells may approach that observed in some diatoms. While cyanobacteria have typically been considered too small to sink to the ocean depths, recent research suggests that these organisms must nonetheless account for some of the carbon dioxide that is constantly being sequestered in the deep ocean.  The presence of dense silica in cyanobacterial cells could explain this paradox by providing a mechanism to speed the sinking rate of particles containing these organisms.  Thus, the ability of the ocean to sequester carbon may be tied to growth of cyanobacteria, as well as to diatoms.

The ability of these tiny bacteria to take up silicon also may be of interest to those working on energy efficient production of computer chips.

“Diatoms are the envy of the engineering world for their ability to construct tiny complex structures of mineral silica at much lower energetic cost than incurred by computer chip makers,” said Baines. “But unearthing the secret of this biochemical trick has been challenging.”

Cyanobacteria, on the other hand, are much simpler organisms than diatoms, and the genomes of many strains have been sequenced.  If the silicon in these cells is truly mineral silica, it may be that these organisms are better models for developing a biomimetic approach to nano-fabrication of silica chips.

Bigelow Laboratory for Ocean Sciences is an internationally known, independent, non-profit center for global ocean research, ocean science education, and technology transfer.  A recognized leader in Maine's emerging innovation economy, the Laboratory’s research ranges from microbial oceanography to the large-scale biogeochemical processes that drive ocean ecosystems and global environmental conditions.