The 2 inches of ropey biofilm under study was two-tenth of an inch in diameter. Microscopic images of the rope show that some of the single-celled organisms have shapes that intertwine with each other and some have tendrils.
"We do not know why the have the shape they do," says Macalady. "Microorganisms in them likely secrete some sticky goo, an extra-cellular polymeric substance -- slime that holds them together."
What the researchers do know is that the location where these ropes grow is very low in available energy -- considered an energy-limiting environment. The location can support only very slow growth. The ropes range in length from one to two meters, and radiocarbon dating places them at 1,000 to 2,000 years old.
"Previous researchers have estimated the rate of cell growth in some deep sea sediments to a cell division every thousand years," says Macalady.
Microscopic images of the rope using three dyes, one for DNA, one for bacteria and one for archaea, show very little activity in the bacteria or archaea, probably because the dyes highlight ribosomes and they only exist in a cell when it is actively metabolizing.
The researchers, who include Macalady; Daniel S. Jones and Rebecca R. McCauley, graduate students, geosciences; Irene Schaperdoth, research associate; and Dan Bloom, undergraduate honors student in astrobiology, are hoping to obtain more microbial rope samples this summer. They will work with divers to get samples from the deepest and shallowest ends of the ropes in order to find clues about how they grow.
|Contact: A'ndrea Elyse Messer|