Of the 2,033 proteins detected, 572 were unique to the biofilm bacteria. One of the new proteins produced by the Leptospirillum group II bacterium appears to be a key protein in the production of acid mine drainage. The protein, a cytochrome, oxidizes iron, and thus controls the rate of production of acid mine drainage.
"This is how it gets its food, this is its mechanism for harvesting energy from the environment," said Banfield. "It's probably the first step in the electron transport chain associated with the metabolism of the organism."
Interestingly, many of the proteins produced by the biofilm bacteria are responsible for maintaining correctly folded proteins and defending against free radicals, "suggesting that these are significant challenges in this hot, acid environment," she said.
"One of the most interesting things we found is that there are large numbers of proteins that don't resemble any other proteins we know about. Many are enzymes that function to maintain the correct structure of other proteins that are exposed to the unusually harsh acidic environment," added Michael Thelen, a protein biochemist at Lawrence Livermore National Laboratory.
Last year's paper reporting the community genome showed that a minor organism in the community, a Leptospirillum group III bacterium, was responsible for a key function: fixing nitrogen from the atmosphere. The new proteome confirms that this is a keystone species in more ways than one.
"We were somewhat surprised to see that Leptospirillum group III, that same minor organism, is also taking a lion's share of the responsibility in producing the extracellular polymers that mak