Ocean Sampling
To isolate bacteria from the ocean, we used a small rubber boat called a Zodiac to
go to many sites out on the water. We used the global positioning system (GPS) to find these sites. Once we arrived at each site, we sent down containers to specific depths and collected a water sample.
Later, back in our lab, we passed the water samples through a 0.8-micron filter to trap the phytoplankton. Next, we passed the filtrate from the 0.8-micron filter through a 0.2-micron filter to trap the bacteria. This system works because phytoplankton are much bigger than the bacteria, so we can separate the two types of organisms by using filters of decreasing size. 
We collected our samples at different depths because the types of light called UVA and UVB penetrate the ocean to different depths. UVA can penetrate deeper than UVB. Both UVA and UVB cause damage to living cells. UVB is absorbed by a cell's DNA, which causes all sorts of damage. UVA produces "free radicals" in cells that act on DNA and cause indirect damage. So how deep an organism is in the ocean determines what kind of DNA damage it will receive. Phytoplankton and bacteria in the ocean repair these two types of damage in different ways. By studying this plankton we can see how they were damaged and how well they repaired themselves.