Polar Science Station: The Case of the Elusive Element

Week 5
31 July 2006

Searching for the Elusive Element Using Biological Oceanography

Part I
The Azam Group

1. What is the objective of the project?

The objective is to collect information about the bacteria found in these waters at this time of year (winter).

Question: What are bacteria? What processes are bacteria responsible for? Someone hands you a food that is full of bacteria. Under what circumstances would you consume it? (See end of this article for a hint).

2. What do bacteria have to do with iron? Bacteria are recyclers.

They are the only organisms that can use dissolved organic materials and make them available in the food chain. Phytoplankton take up iron from the ocean. When the phytoplankton die and decompose, the iron is now part of the dissolved organic material. Phytoplankton cannot absorb the iron in this form. Bacteria are able to take up and use the dissolved organic material, that can be up to 90% of the organic material in the sea. Bacteria are not only recyclers. They are fed on by protozoa, that in turn are fed on by small zooplankton, and so on. In this way, bacteria return dissolved organic matter towards fish and, ultimately, towards fishermen. So it is important to know how much carbon and iron go through phytoplankton and through bacteria.


bacteria - compare size with diatom in picture (long single-celled algae)	instrument used for filtering

3. What information on bacteria are you looking for on this cruise?

We can measure the flux of carbon by looking at:

a) How fast do they grow?

b) How many are there?

c) How many species are there? What kinds are dominant?

4. How do you collect, process, and analyze information?

First, we collect water samples using the TMC rosette.
Next, we start incubations or filter the water.
Then, we analyze the samples.

To measure growth, we add a small amount of radioactive tracer. In this case we use the amino acid leucine to which tritium has been added. Only the bacteria (not phytoplankton or other organisms) are able to uptake the leucine from the water. We incubate bacteria in 2ml vials, at in situ temperature, to allow them time to grow. After few hours, we kill bacteria and centrifuge the vials, to get rid of the water. A liquid scintillation cocktail is added to each vial. We use a “Liquid Scintillation Counter” to measure the amount of tracer that has been absorbed in order to determine the growth rate.


A basic diagram of bacteria

Liquid Scintillation Counter - liquid scintillation counting is a standard laboratory method in the life-sciences for measuring radiation from beta-emitting nuclides	bacteria that are in the grid the portion of the slide that you see in the microscope

To measure quantity, Bacteria are very small and you need a microscope to look at them. So we add a fluorescent stain that binds to DNA and then filter about 10ml of water on a 25 mm membrane. This membrane is then mounted on a slide and put under a microscope, which has a grid with 100 small squares. On each slide we count all the bacteria that are in the grid, from 20-30 fields (the portion of the slide that you see in the microscope). We determine the average number of bacteria found in that area and use a transformation factor to determine how many bacteria there are in one ml of water.

To measure composition, (We do not do this on board ship; we wait until we are back at our lab.) On board, we filter about 9 liters of water (using a 0.2 micron filter) onto a membrane and then, in the lab, extract the DNA from the bacteria. Then we use the DNA to identify the kind of bacteria that are present in the sample.


Maura Manganelli Biography

5. Why is this research important?

We don’t know much about the processes of bacteria in the ocean. However, without bacteria, the food chain would not exist. Bacteria are essential to the health of the ocean and the planet.

Hint for the bacteria food question:
Do you ever eat yogurt?

The research group: Farooq Azam, Distinguished Professor, Scripps Institution of Oceanography, UC San Diego; Maura Manganelli, Researcher, National Institute for Occupational Safety and Prevention, Rome, Italy; Ty Samo, PhD student, Scripps Institute of Oceanography; Johnny Ngyuen, undergraduate, UC San Diego.See "The Team" for their biographies.

Week 5 31 July 2006

Searching for the Elusive Element Using Biological Oceanography

Part I The Azam Group

Week 5
31 July 2006

Part I
The Azam Group