Clams Convert Air Into Food

Jan 16, 2008
Clams Convert Air Into Food
Bacteria in a shipworm allow it to manufacture food from the nitrogen content in air. Credit: Ruth Turner, Harvard Museum of Comparative Zoology

Only plants can take nitrogen gas from the air and use it to make the protein they need to grow. Or so biologists thought.

Now scientists at Ocean Genome Legacy in Ipswich, Mass., and their colleagues at Harvard Medical School have shown that animals, too, can convert air into food. The National Science Foundation (NSF) funded their research.

The animals are marine clams called shipworms. They burrow into and eat wood, causing more than a billion dollars in damage to ships and piers each year.

"Wood has very little nutritional value," said biologist Dan Distel, executive director of Ocean Genome Legacy. "It contains almost no protein. But these clams use bacterial symbionts living inside a special organ in their gills to convert dissolved air [which is about 80 percent nitrogen] into the protein they need."

The discovery reveals a new way for animals to feed and suggests that other animals in the sea and elsewhere may be able to survive with only air as a source of protein.

Understanding how these clams make use of this process is also helping researchers gain insights into how plants fix nitrogen, responsible for a large percentage of the protein made by plants and ultimately eaten by livestock and humans, said Distel and colleagues Claude Lechene and Gregory McMahon of Harvard Medical School and Yvette Luyten of Ocean Genome Legacy.

Using multi-isotope imaging mass spectrometry (MIMS), they directly imaged and measured nitrogen fixation by individual bacteria in host cells, and demonstrated that fixed nitrogen is used for host metabolism. "This approach," said Lechene, "introduces a powerful new way to study microbes and global nutrient cycles."

Bacteria and archaea responsible for biological nitrogen fixation can be found in free-living form or in symbiosis with algae, higher plants and some animals. Although these microbes are a critical part of the global nitrogen cycle, "there has previously been no means to evaluate this fixation process at a subcellular resolution," said Lechene. "This is now possible with MIMS."

Wood and woody plant materials are abundant in the biosphere and are important carbon sources for fungi and microorganisms. But few animals are able to feed primarily on wood.

Although rich in carbon, said Distel, wood contains two orders of magnitude less nitrogen per unit of carbon than does animal tissue. Animals using wood as food must therefore obtain other sources of combined nitrogen for biosynthesis. Wood-eating termites, for example, supplement their diet with nitrogenous compounds produced by nitrogen-fixing bacteria in their gut.

Along came shipworms, able to do the same thing.

"Although conspicuous communities of nitrogen-fixing bacteria have not been found in the guts of shipworms," said Distel, "dense populations of intracellular symbionts have been observed in cells in shipworm gills." A bacterium capable of fixing nitrogen gas has been isolated from the gills of shipworms.

Distel, Lechene and co-workers localized and measured nitrogen fixation by individual cells of the bacteria using MIMS to measure the incorporation of nitrogen gas enriched in the rare stable isotope 15N. "MIMS technology has allowed us to localize, quantify, and compare nitrogen fixation in single cells and subcellular structures," said Distel.

Indeed, it turns out, animals--or at least this clam--can make food from thin air.

Source: NSF

Explore further: Researchers collect soil samples from around the globe in effort to conduct fungi survey

add to favorites email to friend print save as pdf

Related Stories

Legume research uncovers nitrogen uptake genes

Apr 01, 2014

(Phys.org) —Increased nitrogen-use efficiency of plants and an associated reduced need for nitrogen-based fertilisers may be a step closer following University of Adelaide research on legumes.

Recommended for you

Parasitic worm genomes: largest-ever dataset released

10 hours ago

The largest collection of helminth genomic data ever assembled has been published in the new, open-access WormBase-ParaSite. Developed jointly by EMBL-EBI and the Wellcome Trust Sanger Institute, this new ...

Male sex organ distinguishes 30 millipede species

10 hours ago

The unique shapes of male sex organs have helped describe thirty new millipede species from the Great Western Woodlands in the Goldfields, the largest area of relatively undisturbed Mediterranean climate ...

How can we avoid kelp beds turning into barren grounds?

14 hours ago

Urchins are marine invertebrates that mould the biological richness of marine grounds. However, an excessive proliferation of urchins may also have severe ecological consequences on marine grounds as they ...

User comments : 0

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.