Picturing the world of ocean microbes

February 5, 2010

Streaming matter! Exploding organisms! Sinking particles! These are some of the things that populate the world of oceanic bacteria, providing the microorganisms with nutrition and perhaps exercise as they race for food, according to CEE Professor Roman Stocker, who is among those who have challenged the traditional view that ocean bacteria rarely swim, but passively wait for food to reach them.

In order to illustrate this concept, Stocker, who studies the fluid mechanics and ecology of ocean microorganisms; artist Glynn Gorick; and former postdoctoral associate Justin Seymour, now a senior research fellow at the University of Technology Sydney, created an image of this dynamic seascape.

The image was selected by Science magazine to grace the cover of its Feb. 5 issue, which highlights the Gordon Research Conferences, a 75-year-old nonprofit organization that will run 400 conferences on different topics in 2010. CEE science writer Denise Brehm interviewed the scientists and artist about their collaboration.

What are we looking at in this image?

Justin: We are looking at the world experienced by a bacterium living in the ocean. For a long time it was assumed that the microscale world experienced by these microbes was fairly homogeneous. This image shows that this microscale world is in fact extremely patchy, structured and dynamic, and highlights that marine bacteria, just like larger foraging organisms, can exploit discrete resource islands. This has implications for overall bacterial growth and production, competition between different microbial populations, and the cycling of carbon and other important chemicals in the ocean.

Roman: Up to 20 years ago, the ocean was described as a "homogeneous soup" at small scales (meters and below). In that scenario, everything was well mixed at these small scales, and small organisms would not have had reason to be motile. Recent research, however, has painted a different picture: the ocean is highly structured and heterogeneous even at minute scales. That is, even marine microbes experience a very dynamic seascape. The image shows a few examples of processes that contribute to create this patchy, dynamic seascape.

The trails and patches represent dissolved organic matter, which serves as nutrients for bacteria. At the top left we show excretions of dissolved organic matter by larger organisms, like zooplankton. At the top left center and bottom right we show the release of such matter by two phytoplankton cells, which creates a high-concentration region to which bacteria are attracted. On the top right, we show the death of a phytoplankton by lysis, possibly due to viral infection. The lysis creates a violent burst of dissolved organic matter. At the center of the image, extending along its height, we show the plume of dissolved organic matter created by a settling marine snow particle. The main actors in the image are motile bacteria, which are swimming by use of their helical flagella.

And is that spherical object at top center meant to be a single phytoplankton?

Roman: Yes, it's called a Coccolithophore, because it carries — phore — little scales — coccoliths. We chose it as a representative phytoplankton; we could have chosen others.

How big would these microbes and this cube be in reality?

Roman: The cube represents 1 milliliter of seawater. That is, it's 1 centimeter on each side. The bacteria are about 1 micrometer in size; the phytoplankton, about 10 micrometers. The zooplankton and marine snow particle could be 100 micrometers to 1 millimeter.

Why should we care about these microbes?

Roman: These microbes represent a crucial link in the marine food web. They are the main players in the oceans' biogeochemical cycles, for example the carbon cycle. These organisms include the phytoplankton, which are the primary producers that enable all life in the ocean. Then there are the heterotrophic bacteria, which are recyclers; they are the only ones who can take up dissolved organic matter that would otherwise be lost from the food web, thereby exerting a fundamental control on the budgets of the elements — like carbon, nitrogen and phosphorus — and on the productivity of aquatic ecosystems.

Why did you have this image created?

Justin: Because seawater appears clear and empty to the naked eye, it's often difficult to comprehend the level of ecological complexity occurring within each individual drop. So our objective was to illustrate graphically some of the ecological processes occurring within these drops of seawater.

Roman: The world of microbes escapes our intuition, because it is so much smaller than ours and the dominant physical processes are rather different from those that dominate our everyday life. An image makes these microscale processes more intuitive and calls attention to the importance of a world that — in virtue of its size — is poorly known, yet extremely important. Work in our laboratory focuses on visualizing the movement of organisms at these small scales, hence a graphic representation of what this micro-world looks like came as a natural extension of our research.

How did you start working with Glynn?

Roman: Glynn has a bit of a reputation in the field, and already had produced several images of marine processes. I saw one of his images at a conference and decided to get in touch. I thought there was great potential in linking his amazing skills in making the ocean come to life with our research on marine microbial ecology.

Glynn, your artwork is beautiful! How do you make each microbe's appearance accurate?

Glynn: Well thanks a lot, Denise! I search for photographs of the larger organisms such as the 1 millimeter size shrimp-like animal — Calanus finmarchicus — and electron micrographs of the very small members of the plankton community, for example, the single cell plant alga Emiliania huxleyi or Ehux shown at top left center and the bacteria cells with helical swimming appendages, the viruses, etc.

This 1 milliliter or 1 cubic centimeter of normal sea water from the surface sunlit zone may contain 10 Ehux cells, 1 million bacteria cells and 10 million virus particles, plus an occasional C. finmarchicus scudding upwards or sinking downwards. The marine snow particle is slowly sinking, leaving a trail of dissolved organic matter, which as Roman and Justin demonstrate in their research, is an attractant to swimming bacteria.

You're all on different continents. What are the logistics for this collaborative project - in both physical and intellectual terms?

Justin: All of the communication was done remotely, via email conversations. Roman and I came up with the original idea and we had clear ideas of what processes should be included in the image. And Glynn brought to the table great insight into the scientific processes, as well as excellent design ideas.

Roman: Glynn was great at accommodating all our requests and changes. Typically, Justin and I would discuss the latest version of the image, compile a list of requested changes and send that to Glynn, who prepared the next iteration and often sent us more than one alternative to choose from. I believe there were around 30 iterations for this image!

The key to making this work is to remain open-minded on both sides, and this worked really well in this case. Glynn has a good background in marine processes, but was always keen to learn more; we had precise ideas on what we wanted, but often no clue on how to implement these ideas, and were thus guided by Glynn.

One example is the representation of the chemical plumes and patches. Justin and I had this world of chemical trails in mind, but we had serious doubts that it could be represented graphically in a simple yet intuitive way. Glynn was great at exploring various options with us and ultimately came up with what I think is a really nice solution.

How do you create these images? What's the medium?

Glynn: I used to make detailed pencil drawings, which I then made into oil paintings. I started this line of work about 16 years ago when I chose photosynthesis — a key process for life on Earth — as a subject for a painting. Then I got a computer to enable me to alter color and shape very easily so that I could try out many combinations of styles and objects in the design.

Can you tell me a little about your creative process?

Glynn: The process is a bit like setting one snapshot of a scene in a stage play. The first job is to have the best possible script. In this project the research scientists write the play, I make and position the main characters, and we arrive at a best scene layout. For instance, Roman and Justin directed me on the structure of the bacteria and how they accumulate around the food source. The final job is to alter the background color and texture to make it as accurate a representation as possible. Roman and Justin gave me very detailed direction and the fine-tuning really was very fine.

I understand that you were once a science teacher. Your current work seems to be a perfect melding of your interests in science education and art.

Glynn: These images over time are adding up to a resource that I would like to develop as a teaching tool — a visual communication device. If I were making a school science image here I would say this is a drifting community of huge numbers of very small individuals of many different species occupying the largest living space on the planet. The producers are the small algae plants (phytoplankton) harvesting sunlight and making food. The consumers are the animals (zooplankton mostly, plus fish and eggs) and the bacteria are the vital decomposers recycling nutrients. They then release nitrates and phosphates essential for plant growth, and the oxygen essential for animal life in the seas and on land.

What are your next steps in this work?

Roman: As movement is an essential feature of life in the micro-world, it will be interesting to pursue animation as the best way to convey this. I know that Glynn has been thinking along these lines, and my group is working on the development of an educational video game called "Virtual Microbe" with the same purpose.

Glynn: I have made short animated movie clips of the viral infection of Ehux cells, signaling between bacteria, and microbes in the evolving "tree of life." I am keen to work on ways of showing movement of chemicals between marine microbes that relates to global chemical cycles. I hope there are ways to continue our collaboration and widen its reach.