Microbe Loves Acid

If a sulfur snack followed by a scorching swim through plumes of low-pH seawater sounds appealing, you may have a friend in Aciduliprofundum boonei. It's the first acid-loving bug to be cultured from a hydrothermal vent, and it may be a key player in sulfur and iron cycling at deep-sea vents (Nature 2006, 442, 444).

"Microbes are the chemists of the world," says Anna-Louise Reysenbach, a microbial ecologist at Portland State University, in Oregon, and lead author of the study. "Wherever there's a little bit of chemistry, a redox reaction or otherwise, that could give you some energy, you will find a microbe that can use it." In particular, A. boonei gets its energy from oxidation of organic carbon coupled with sulfur or iron reduction.

Because hydrothermal vents are highly acidic, researchers have long wondered why no one has isolated an acid-loving microbe, as they have from acidic pools in Yellowstone National Park. While cruising near a South Pacific vent with a pH below 3, Reysenbach saw her opportunity.

It's not hard to get "the weeds of the hyperthermophiles" to grow, comments Jan Amend of Washington University in St. Louis. "But culturing and isolating the interesting bugs-that's the challenge! Reysenbach et al. cultured an organism that some people have called 'unculturable.' "

Indeed, the microbe Reysenbach managed to grow belongs to a branch of Archaea that had long been on her radar screen. "We've detected this bug at all deep-sea vents through culture-independent techniques. We knew they were there, we knew they were important, but we had no idea what they were doing."

Reysenbach says in addition to providing insight on sulfur and iron cycling, the microbe might also be used in biomining, where microorganisms are used to extract valuable metals remaining in mine tailings.