In addition to experimenting with nutrient levels and temperature, he's using very low light levels, since he believes very little infrared light reaches the bacteria through the ice covering these lakes. He already has one species in culture from Lake Fryxell. Sometimes these things purify easily and sometimes they don't. I know there are some other organisms in there. But I think we have something that will grow reproducibly for us, and that's always the start.
Green plants use light energy and electrons from water to convert carbon dioxide into cell material.
Lake Fryxell has high levels of hydrogen sulfide, which is produced by other kinds of bacteria living in the sediment at the bottom of the lake. The sulfide is soluble and slowly percolates up through the water column to a certain level. But you collect at 9 meters and man, it just knocks your socks off. There's a very distinct line, and it's nice to track bacteria through that line. The trick for the photosynthetic bacteria is to live high enough in the lake that they get sufficient light, but low enough that they get sufficient sulfide.