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Fungus growing ants as model systems

Social insects make good model systems for studying symbiosis, the close and long-term interrelationship between different species. An EU-funded initiative examined the bacteria in the guts of attine ants, an almost unknown component of the symbiosis between the farming ants and the fungus gardens they maintain for food.
Fungus growing ants as model systems
The fungus-farming attine ants are used by scientists as model systems for how mutualistic (co-)evolution shapes obligate cooperation between species and regulates conflict between the ant family members involved and between host colonies and their fungal symbionts. However, very little research has been conducted into the microorganisms found in the guts of this ant lineage which evolved more than 50 million years ago. The nitrogen limited diets suggest they may have gut bacterial symbionts to preserve nitrogen and boost their nutritional efficiency.

The EU-funded GUTS (Gut symbiomes of fungus-growing ants) project was established to identify putative bacterial gut symbionts across the genera and species of attine ants, including their tissue specificity and their function in the guts, in order to reconstruct the stepwise advancement of the symbiosis from small scale subsistence farming to almost industrial scale farming.

A range of techniques were used to demonstrate that the attine gut microbial community mostly featured Alpha-Proteobacteria and Mollicutes classes of bacteria and with just a few dominant strains. The presence of prokaryotic nifH genes in the ant gut revealed that some of the microorganisms identified play a role in nitrogen preservation. This was confirmed using a specific NifH antibody, which showed that the ileum and rectal papillae are the compartments of the gut where nitrogen preservation takes place.

The study also found that gut bacteria were being affected by the presence/absence of antibiotics-producing actinobacteria on the ant cuticle. Ant species without these cuticular bacteria appeared to have more unstable gut bacterial communities. A further study was conducted on the model system Acromyrmex echinatior to determine possible connections between gut bacterial communities and kin recognition . Researchers subjected 2 000 ants from 4 different colonies to different diets, causing either slow or rapid loss of the ants’ gut bacteria or enhancing the diversity of these gut bacterial communities. Researchers then conducted aggression tests between nest-mates and non-nestmates, obtained cuticular hydrocarbon profiles, and also analysed the final gut bacteria profiles.

GUTS results will help to bridge the divide between molecular biology and evolutionary biology by answering fundamental questions concerning symbiosis in a social insect model system.

Related information

Keywords

Symbiosis, attine ants, fungus gardens, Alpha-Proteobacteria, Mollicutes, NifH gene, Acromyrmex echinatior
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