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September 2011 Issue

Hydrogen-Powered Bacteria Found in Deep-Sea Vent Mussels
During a recent expedition to hydrothermal vents in the deep sea, researchers from the Max Planck Institute of Marine Microbiology and the Center for Marine Environmental Sciences (MARUM) discovered mussels have a form of symbiotic bacteria that use hydrogen as an energy source.

Their results, published in an August issue of Nature, suggest the ability to use hydrogen as a source of energy is widespread in hydrothermal vent symbioses. Until now, only two sources of energy were known to power chemosynthesis by symbiotic bacteria at hydrothermal vents: hydrogen sulfide and methane.

"We have now discovered a third energy source," says Nicole Dubilier from the Max Planck Institute, who led the team responsible for the discovery.

The discovery began at the Logatchev hydrothermal vent field, at 3,000 meters' depth on the Mid-Atlantic Ridge. In the gills of the deep-sea mussel Bathymodiolus puteoserpentis, the researchers discovered a sulfur-oxidizing symbiont that can also use hydrogen as an energy source.

To sample these mussels, researchers deployed two deep-sea ROVs, MARUM-QUEST from MARUM at the University of Bremen and KIEL 6000 from Leibniz Institute of Marine Sciences. Researchers were then able to identify the mussel symbiont hydrogenase, the key enzyme for hydrogen oxidation.

The deep-sea mussel symbionts therefore play a substantial role as the primary producers responsible for transforming geofuels to biomass in these habitats. Even the symbionts of other hydrothermal vent animals such as the giant tubeworm Riftia pachyptila and the shrimp Rimicaris exoculata have the key gene for hydrogen oxidation, which had not been previously recognized. For more information, visit www.mpg.de.

Recurring Patterns of Viruses Seen in the Open Ocean
Viruses have a significant effect on ocean biology, specifically marine microbiology, according to Craig Carlson, a professor of biology at the University of California, Santa Barbara (UCSB), and collaborators.

Carlson was the senior author of a study of marine viruses published in August in the journal of The International Society for Microbial Ecology.

The new findings, resulting from a decade of research, reveal recurring patterns of marine virioplankton dynamics in the open sea, which have implications in the understanding of nutrient cycling in the ocean.

In the paper, the authors describe regular annual patterns of virioplankton abundance, tied to ocean physics and chemistry. These patterns in turn control the dynamics of the bacterioplankton hosts. The data suggest that a significant fraction of viruses in the upper photic zone of the subtropical oceanic gyres may be cyanophages, viruses that infect photosynthetic bacterioplankton.

If true, the dominance of cyanophages in open-ocean systems has significant biogeochemical implications. Viral-mediated breakdown of cyanobacteria could benefit phytoplankton through the release of macro- and micronutrients. Viral breakdown of host cells converts particulate material to suspended or dissolved materials such as amino acids and nucleic acids, effectively resulting in the retention of nitrogen, phosphorous and iron within the surface water. These dissolved materials fuel microbial activity in an otherwise nutrient-poor, open-ocean system.

The scientists studied the temporal and vertical patterns of virioplankton abundance within the open ocean. Beginning in 2000, samples were collected throughout the upper 300 meters of the water column every month at an open-ocean hydrostation called the Bermuda Atlantic Timeseries Study (BATS) site.

The additional data collected as part of the BATS program provided oceanographic details regarding ocean physics, chemistry and biology that are valuable for interpreting the observed trends in marine phages.

"This high-resolution, decadal survey provides insight into the possible controls of virioplankton dynamics and the role they play in regulating biology and nutrient cycling in the open ocean," Carlson said. "The data provided by this study will now be utilized by ecosystem and biogeochemical modelers in an attempt to better understand how microbial processes affect the larger biogeochemical cycling in the ocean."

For more information, visit www.ia.ucsb.edu.

Study Suggests New Approach to Sustain Catch of Forage Fish
Reduced catches of small oceanic forage fishes such as sardines and anchovies may be required in some ocean areas to protect the larger predators that depend on them for food, a study published in Science in July said.

Forage species are often the main food source for larger fish, marine mammals and seabirds. Lead author Tony Smith of Commonwealth Scientific and Industrial Research Organisation said these fishes account for more than 30 percent of fisheries production, and demand is rising.

The study used three models to examine ecosystem effects when forage fish were harvested at levels maximizing sustainable yield. The scientists found impacts both positive and negative, varying across forage species, ecological groups and ecosystems.

The greatest impacts were seen for forage species that dominate their local food supply, such as Peruvian anchovy in the northern Humboldt ecosystem, and for forage species that are highly connected to many other species across the food web.

Some ecological groups declined by more than 60 percent as a result of forage fishing at conventional levels. Marine mammals and seabirds were often affected.

"The modeling showed that halving fishing rates for the high-impact species would greatly reduce the impact on ecosystems, while still achieving 80 percent of the maximum sustainable yield," Smith said, adding that reduced fishing could "improve economic outcomes for forage fisheries while also improving yields for some other commercial species."

He said these results could be combined with other measures, such as closing areas near marine mammal and seabird breeding colonies to fishing, to meet ecological objectives while ensuring forage fish continue to contribute to food security.

For more information, visit www.csiro.au.



2012:  JAN | FEB | MARCH | APRIL | MAY | JUNE | JULY | AUG | SEPT | OCT | NOV | DEC
2011:  JAN | FEB | MARCH | APRIL | MAY | JUNE | JULY | AUG | SEPT | OCT | NOV | DEC

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