'Dead-zone' microbe measures ocean health

Canadian and U.S. researchers have mapped the genome of a microbe that lives in ocean "dead zones," areas of low-oxygen water that are expanding because of climate change.

Researchers at the University of British Columbia and the U.S. Department of Energy say the microbe, called SUP05, is the most abundant organism in these oxygen-minimum zones and plays an important role in their ecosystems.

Because of this, SUP05 is a useful indicator for the overall health of ocean ecosystems, the scientists said in a study published in this week's issue of Science.

"Our analysis showed this microbe to be a key biological indicator of oceanic dead zones," said Steve Hallam, a professor of microbiology and immunology at the University of British Columbia.

Dead zones are areas of ocean water with low concentrations of dissolved oxygen, found off the coasts of B.C., Chile, Namibia and elsewhere. They are expanding, and research attributes their growth in part to global climate change.

As well, dead zones are themselves a source of greenhouse gases and draw in nitrogen, an important nutrient for sea life, meaning they can affect the productivity of fisheries and the health of ocean ecosystems.

Microbes like SUP05 are able to survive in the dead zones because they "breathe" other compounds instead of oxygen, such as nitrates, sulphates and metals.

The scientists studied SUP05 in Sannich Inlet, a fjord on Vancouver Island that acts like a natural laboratory for organisms in low-oxygen environments.

The microbe's genome, the map of its complete genetic sequence, indicates that it is related to microbes that metabolize sulphur and live on the gills of deep-sea clams and mussels. But while these symbiotes use oxygen in their energy metabolism, SUP05 uses nitrate.

This is the first time the metabolism of carbon, sulphur and nitrogen has been linked genetically in one dead-zone microbe, the scientists said.

The researchers found that SUP05 plays an important part in their ecosystem but also creates byproducts that have a negative impact on the climate.

"Specifically, SUP05 removes toxic sulphides from the water and fixes carbon dioxide, but we also think it's producing nitrous oxide, which is a more potent greenhouse gas than either carbon dioxide or methane," Hallam said.

Little is know about the metabolism of organisms in dead zones, so the genome of SUP05 is only the beginning of the research, the scientists said.

"The genetic blueprint of SUPO5 opens the door to studying the who's who of dead zone ecology and provides an experimental framework for asking an entirely new set of research questions," Hallam said.