Bacterial Symbionts Provide Nitrogen

small orange ants walk along a twisted branch as they carry leaves

Biological Strategy

Leafcutter ants

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Capture, Absorb, or Filter Chemical Entities

Living systems often require chemical elements and chemical compounds, including complex sugars, proteins, and odor-making compounds, to perform critical activities. These compounds exist in various states–solid, liquid, and gas–and are ubiquitous in soil, water, and air. This requires that living systems not only have ways to capture, absorb, or filter them, but also ways to differentiate among them, selecting those that are valuable or harmful. For example, mangrove trees live with their roots in salty water and sediments. Various mangrove species have different strategies for removing salt from the water they take in so that their tissues can use the fresh water.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Leafcutter ants likely obtain a large part of their nitrogen from symbiotic bacteria living in their cultivated fungal gardens.

Where Are the Ants Carrying All Those Leaves?

“Bacteria-mediated acquisition of atmospheric N₂
serves as a critical source of nitrogen
in terrestrial ecosystems. Here we reveal that symbiotic
nitrogen fixation facilitates the
cultivation of specialized fungal crops by leaf-cutter
ants. By using acetylene reduction
and stable isotope experiments, we demonstrated that N₂
fixation occurred in the fungus
gardens of eight leaf-cutterant species and, further, that this fixed nitrogen
was incorporated into ant biomass.
Symbiotic N₂-fixing bacteria were
consistently isolated from the fungus
gardens of 80 leaf-cutter ant
colonies collected in Argentina,
Costa Rica, and Panama. The discovery of
N₂ fixation within the
leaf-cutter ant–microbe reveals a
previously unrecognized nitrogen source in
neotropical ecosystems.” (Pinto-Tomás et al. 2009:1120)

http://scienceonline.org/cgi/content/abstract/326/5956/1120
http://schaechter.asmblog.org/schaechter/2010/01/lea.html

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