Submersible Incubation Device (SID)

The main idea leading to the instrument developed by Woods Hole Oceanographic Institution (WHOI) Oceanographers was to automatically run microbiological incubations in situ – in this case underwater. This was deemed necessary in order to avoid having to bring the samples to the surface in order to incubate them, because by doing this, the samples would not be in the same habitat in which they live and would be subjected to different pressure, temperature, light, and other conditions, which would probably alter the way they function.

The SID concept began to unfold more than 30 years ago through the vision of microbiologist Craig Taylor and engineer Ken Doherty at WHOI. They wanted a way to see exactly what the multitudes of microbes in the ocean were doing. It took many decades for the necessary technology to become available, as the robotic submersible mini-lab would have to take in samples of precise volumes at specific depths, incubate them, stop the incubations at specified times, and preserve the samples for later retrieval. A major problem was how to stop the incubation. In a normal lab, this is done by running the samples through a filter, where, for example, phytoplankton cells trapped on the filter get exposed to an airborne preservative, stopping their chemical reactions. That would not work in a SID. “It’s all still in water, so the cells won’t die right away,” said Taylor. “There are also bacteria there. Well, for them it’s the dinner bell. Over the next couple of days, all of the phytoplankton would slowly die, and then the bacteria would decompose that organic matter and turn it back into CO2.

So you’ve destroyed the very measurement you set out to make.” Adding a preservative to the filtered cells would do the trick, but doing so under water was complicated. It required synchronizing the filtering with injections of preservative. After a few rounds of trial and error, Taylor and Doherty came up with the “Fixation Filter.” It takes advantage of the fact that the preservative for these experiments is less dense than seawater, so it tends to rise through seawater if given the chance. While the sample cells are being filtered, the Fixation Filter holds the preservative in a closed reservoir below the filter, except for 2 small holes. When filtering stops, the preservative flows up through one hole as denser seawater in the filter chamber moves down through the other. Within 15 minutes, the cells on the filter are immersed in preservative. Best of all, it works with no moving parts. This is the world's first subsea incubation system in operation and development is ongoing in order make the system even more efficient, while allowing it to go deeper and to sample a wider range of microbes.

Source: Oceanus Magazine

Excerpts from:

An Ocean Instrument Is Born

Meet SID: the Submersible Incubation Device