Updates From Sea | Cruise 2007
February 3rd
By Eric Simms, Education Outreach Coordinator
Small Organisms Pack a Big Punch at Deep Sea Vents
Each one is only a single cell, but collectively they make life at deep-sea vents possible. Most of their identities remain a mystery - and we don't even know how many different types may exist. What are they? Bacteria, of course!
White bacterial mats coat these new basalt rocks. Photo © E. Simms
Bacteria are known to be an essential component of vent ecosystems - one reason is because certain types use chemosynthesis to create sugars and other compounds from hydrogen sulfide in the vent fluids. These sugars and other compounds are used for energy by the bacteria, as well as by other animals that have a symbiotic relationship with the bacteria. It has also been suggested that bacteria living at new vents may provide chemical signals that attract other animals (for example, tubeworm larvae) to the vents. Scientists still don't know the exact identity of most of the bacteria at the vents, but a group of microbiologists led by Dr. Costantino Vetriani (Rutgers University) and Dr. Stefan Sievert (Wood Hole Oceanographic Institution) are trying to change that aboard this cruise. The group has been working to find out which types of bacteria live at vents and what their role is in this unique ecosystem.
Click here for pictures of the Microbiology group at work.
Testing acidity in bacteria cultures. Photo © E. Simms
Identifying species of bacteria, and how they function, can be difficult and time consuming - bacterial cells are very small, and many different species are often mixed together in a single small sample from the seafloor. The first step is to try to separate different types of bacteria from one another in the same sample. This is done by exposing the bacteria in the sample to different conditions and seeing if they grow - each set of different conditions is called a culture. For example, if you wanted to separate bacteria that use hydrogen sulfide for energy from other bacteria in the same sample, you could create two different cultures. Both cultures would include the exact same nutrients, but one of them would also have hydrogen sulfide added. After placing a small amount of the sample in each culture, bacteria found growing in the culture with the hydrogen sulfide (but not the other culture) can be assumed to live in an environment with that chemical.
By creating many different cultures with different combinations of nutrients, chemicals, and temperatures, you can separate different groups of bacteria from one another. But what about identifying individual species? Well, when a single bacterial cell grows in a culture, it multiplies to form a colony of many duplicate cells. Once the microbiologists know they have a pure culture of one type of bacteria, they can determine the sequence of genes that are unique to that one species. They can also locate specific genes in the bacteria that tell them about its metabolism (how it makes energy and what chemicals it uses). Most of this work is done back home in the scientists' labs where they have the necessary equipment.
Dr. Sara Borin of Rutgers University works into the night preparing cultures. Photo © E. Simms
So far, the microbiologists on this cruise have collected many samples of bacteria in the water and on rocks at both high- and low-temperature vents. They have used the techniques described above to culture bacteria and prepare samples here on board that they will analyze later in their labs on shore. As the microbiologists learn more about the individual bacteria species at vents (and how they change over time), they can look for patterns to learn more about how the fluid chemistry, bacteria, and animals interact in these fascinating ecosystems.
