1:56 p.m., Sept. 11, 2008----They're miniscule--more than a million of them can fill a space the size of a pencil tip--but marine microbes, microscopic bacteria and plants living in our oceans, play a big role in some of the environment's most important processes.
They are known to impact the carbon cycle, a complex series of exchanges that occur among the atmosphere, land and ocean. Carbon occurs naturally in the earth's atmosphere--mainly in its gaseous form, carbon dioxide--but certain human activities, such as the burning of fossil fuels, can contribute to increased levels of the gas, strengthening the “greenhouse effect” and the subsequent warming of Earth.
By studying microbes, scientists like UD's David Kirchman, an expert on marine microbes who has traveled around the world to study them, can better understand the carbon cycle and in turn learn more about climate change.
This summer, the Maxwell P. and Mildred H. Harrington Professor of Marine Studies published a commentary in the Proceedings of the National Academy of Sciences about the microscopic organisms. His article discusses a new study on the genomes, or DNA sequencing, of microbes. College of Marine and Earth Studies writer Elizabeth Boyle reached Kirchman at his lab at UD's Hugh R. Sharp Campus in Lewes to learn more about the tiniest life at the base of the world's food web.
Why is it important to understand marine microbes?
David Kirchman: The ocean is an important part of the carbon cycle, and as we perturb it by adding more greenhouse gases, carbon dioxide and nitrous oxide being two of those, we need to know more about it.
In order to understand the ocean you need to understand microbes. One kind of microbe, phytoplankton, takes out carbon dioxide from the atmosphere and the other kind, heterotrophic microbes, puts it back in. We and other animals are also heterotrophs (meaning we burn organic carbon to make energy), but heterotrophic microbes are more numerous than humans and other animals and thus important in the carbon cycle. We need to understand the balance between phytoplankton and heterotrophic microbes.
Why is it important to understand that balance?
Kirchman: The balance between phytoplankton and heterotrophic microbes helps to set the amount of carbon that can be soaked up by the oceans. More carbon in the oceans means less in the atmosphere and a smaller contribution to climate change. But higher carbon inputs into the oceans also are causing the oceans to be more acidic, and that's not good. For example, according to a report from the International Coral Reef Symposium held this July in Florida, coral reefs cannot adapt to a more acidic ocean, even if they could to a warmer ocean.
So the ocean is like a sponge and there are these little microscopic critters in that sponge that help it absorb or release carbon?
Kirchman: That's pretty close. It's physical processes that pull the carbon into the ocean and the phytoplankton help keep it there.
Scientists in your field are working to learn exactly how these marine microbes live and function, and to do that they've started looking at their genomes. What is a genome?
Kirchman: The metaphor I use is the blueprint or an instruction book. It's all the information for building life.
What do scientists hope to gain by knowing the genomes of microbes?
Kirchman: There has been this huge push in all of biology to learn genomes. Knowing the genome is the first step in understanding the biology of that organism. It's like a blueprint--you can't say what the organism is doing (by knowing the genome) but it certainly outlines what's possible as far as the types of processes it is able to do.
So it's similar to knowing the DNA sequence of humans and being able to tell whether a particular person will be predisposed to certain types of diseases or will have a certain type of appearance?
Kirchman: Yeah, in some ways it's even more basic because if you are looking at humans you know lots about their biology already, like that they breathe air and walk on two feet on land. With marine microbes you're really looking for more basic information about what they do in the environment. In humans you're looking for extremely subtle differences between people whereas for microbes you're looking at cruder level--trying to figure out what they do.
By studying the genome of one specific kind of microbe, one known as Polaribacter MED 152, researchers recently discovered that it uses light to make energy. What's the impact of this finding?
Kirchman: We used to think that these microbes didn't respond directly to light. So, we didn't think that light affected that part of the carbon cycle (when heterotrophic microbes are making energy). That's a pretty radical change in how we thought about things.
This information will change how we do our measurements. We previously did everything in the dark; now we have to think about the light. It's hard to do experiments in the light because you have to mimic quality of light and intensity in a particular depth.
But also this information could change how we predict the effect of climate change on the ocean and could affect our understanding of the balance between phytoplankton and heterotrophic microbes. Before, we just thought about light affecting phytoplankton and in turn the phytoplankton would affect the heteroptrophs. Phytoplankton use light to create biomass and provide food for the heterotrophs. Now there's a new wrinkle--the direct effect of light on heterotrphs.
What's next the next step for scientists working on this topic?
Kirchman: The study that produced this finding was done on a single, isolated microbe, one of thousands found in the ocean, and the experiments were done in artificial conditions in the lab. We need to find out if other microbes are doing something similar to this one. Then we need to go into the ocean and see what's really happening.
To learn more about Kirchman's work and the College of Marine and Earth Studies, visit [www.ocean.udel.edu].
Photo by Bob Bowden