February 27, 2009

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How long do microbes at the bottom of the ocean live, anyway?

By Katrina Edwards

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This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

Editor's Note: University of Southern California geobiologist Katrina Edwards is taking part in a three-week drilling project at the Atlantic's North Pond—a sediment-filled valley on the ocean floor—designed to locate and study what she calls the “intraterrestrials”: the myriad microbial life-forms living inside Earth's crust. This is a response to a question from a ScientificAmerican.com reader on how long these microbes might live, and whether scientists are concerned about the effects of the test holes they're creating. To track her research ship's current position, click here. To see all her posts, see "60 Seconds in North Pond."

We typically think about "life span" in microbiology in terms of "doubling time," or how long it takes one cell to divide into two. in sediments and rocks, we don't know how long this takes. A year? 10 years? Hundreds of thousands of years? We don't understand these ecosystems well enough to say, but many of us are eager to figure it out.

A really important concept about the upper igneous rock crust - the rock that erupts at mid-ocean ridges and at volcanoes - is that it is very porous and permeable.  Water circulates through this rock readily. Minerals will eventually form from seawater and seal some of the fissures, but this takes many millions of years. Sediments that form on top of rock, in contrast, are not permeable and act like a blanket.

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The flow of water into Hole 395A was tremendous, absolutely, but negligible compared to the naturally occurring inflow of water into the outcrops of rock surrounding the sediment pond. The bottom line is that the water and microbes have plenty of means to get into the crust for the past 7 million years or so, but what they're doing in there is the question.

Researchers Katrina Edwards, Jennifer Biddle and Jess Murati at the launch of the Merian, courtesy Katrina Edwards/USC

Katrina Edwards is a geomicrobiologist who studies the microbiology of hydrothermal sulfides and the igneous ocean crust. She has particular fascination with one common, yet elusive microbial group associated with these deep habitats, the iron oxidizing bacteria. These are the bacteria that make rust. She received her Ph.D. in geomicrobiology from the University of Wisconsin, Madison, in 1999 and spent the following 7 years as a researcher at the Woods Hole Oceanographic Institution, Massachusetts, USA. This is where she "sunk to the bottom of the ocean" and never came back up. She is now a Professor of Biology and Earth Sciences at the University of Southern California, Los Angeles, and is the Director of the Center for Dark Energy Biosphere Investigations (C-DEBI), an NSF sponsored program created at USC expressly for the study of the deep marine biosphere. Katrina has a husband and three children waiting at home for her during this long expedition.

More by Katrina Edwards

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