Thursday 15 November 2012

Symbiotic Bacteria in Snails on the Eastern Lau Spreading Center.

Hydrothermal vents in the deep oceans are colonized by a broad array of invertebrates that have symbiotic relationships with chemotropic Bacteria. These Bacteria are able to derive energy from chemicals discharged by the vents, providing a base for ecosystems entirely separated from the light of the Sun. Not all hydrothermal vent systems are the same; a volcanic field will typically contain a variety of hydrothermal vent systems with different chemical properties, which would imply that different Bacteria would be needed to metabolize the chemicals produced. Ordinarily we would expect different symbionts to have different hosts, but hydrothermal vents tend to have similar faunas to the vents closest to them physically, not those with the most similar chemistry, suggesting that in this instance the hosts are able to form symbiotic relationships with a variety of different Bacteria.

In a paper published in the Proceedings of the National Academy of Sciences, a team of scientists led by Roxanne Beinart of the Department of Organismic and Evolutionary Biology at Harvard University discuss the results of a study into Snails of the genus Alviniconcha at a number of chemically different sites on the Eastern Lau Spreading Center, a divergent plate margin that connects North Island, New Zealand to the islands of Tonga.

Map of the northern  Eastern Lau Spreading Center, showing the four sites from which Snails were sampled. Beinart et al. (2012).

Alviniconcha Snails are widely distributed at hydrothermal vents in the eastern Pacific and Indian Ocean. Beinart et al. sampled them at four sites on the Eastern Lau Spreading Center. The northernmost two of these, Tow Cam and Kilo Moana, are dominated by basaltic lavas, and the southern two, ABE and Tu’i Malila, by andesitic lavas. 

A single Alviniconcha Snail. Beinart et al. (2012).

A colony of Alviniconcha Snails at a vent on the Eastern Lau Spreading Center. Beinart et al. (2012).

Beinart et al. found that each of the Snails was contained Bacteria predominantly from one of three groups. Snails from the two northern, balsaltic, vents were dominated by ε-proteobacteria, while those at the southern two sites by one of two forms of γ-proteobacteria, named the γ-1 and γ-Lau strains.

This suggests that the Snails, and potentially other organisms living in similar ecological niches at hydrothermal vents, are capable of forming symbiotic relationships with different types of bacteria to fit the local environment. This would be a big help to the Snails in colonizing new vent-sites, as it means that planktic larval Snails would be capable of colonizing any vent they encountered, not just ones with suitable chemistry for a specific Bacterial symbiont.

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