Valérie Cueff - Gauchard
Valérie Cueff - GauchardThe complex symbiosis of the hydrothermal shrimp Rimicaris exoculata : from descriptive to functional, thanks to the technological development of a new sampling tool. or The use of different methodological approaches to understand how the shrimp lives on the seabed with its symbionts. |
Rimicaris exoculata is a shrimp that lives in deep-sea hot springs. This shrimp has the particularity of having a large modified head that contains its food suppliers; in other words, symbiotic bacteria that will grow on the chemical elements emanating from the hot springs. During her thesis, Valérie focused on one hand, on the players in the symbiosis. During the reproduction period, this species presents a particular spatial segregation, with females found in dense aggregations near the hot fluids, while the males are dispersed around the periphery of the sites, far away from the fluids. Valérie has therefore compared the symbiotic communities of males and females.
On the other hand, Valérie was also interested in the messenger RNAs of these symbionts; which are molecules that carry genetic information from a gene, located in the DNA, to the cellular machinery that make the proteins needed for the cells to function. But these molecules have a very short lifespan of just a few minutes. Yet, between the time when the shrimps are taken from the bottom and the time when they are collected from the boat, at least 3 hours pass. Therefore, a large part of the information of what is active undersea is lost. To be able to preserve this information, Valérie has led the development of a new technological tool that enables to sample mobile animals like shrimps, and to inject a chemical fixative that preserves the molecules in the state they are when they are collected. Thank to this tool, the molecular signal present at the bottom is preserved until the shrimps are recovered on board the ship.
Why this subject ?
Valérie has been working on this little shrimp for over 20 years. Technologies for genetic studies have evolved a lot during those past few years, and the associated costs have considerably decreased, making studies accessible that weren’t before. Today, we know pretty well the players involved in the symbiosis in this shrimp, but there are still many questions about their functioning together, especially how they function in-situ according to the fluctuating geochemical conditions. Valérie set out to better understand how symbiosis works in this shrimp.
A funny story related to this subject ?
For the preservation of molecules to be effective with the new FISH tool developed during the PhD research, a ratio of 10 volumes of fixative to 1 volume of animal tissue must be maintained. During the initial deployments of the FISH tool at the seafloor, when Valérie was not the onboard scientist in the Nautile submersible, one of the pilots was very proud to tell her he had collected plenty of shrimp in the FISH bowl: “Is that enough for what you needed?”. However, to ensure proper fixation, it was crucial not to exceed about twenty shrimp, and there were nearly 200 in the container this time. So, while Valérie certainly received an abundant sample, for her, quality mattered more than quantity! Unfortunately, the fixation was insufficient. She later asked the pilots to count the shrimp as they were being collected, which amused them, as it is technically very challenging given the density of the aggregates and the opaque bowl. Imagine plunging the narrow nozzle of a vacuum cleaner into a swarm of bees and trying to suck up no more than 20—definitely not an easy task!