Day 13: Adventures in anaerobia

test tubes close up

We know that Zetas, the iron-oxidizing bacteria that have been our primary focus on this cruise, live at the edge of the oxygen minimum zone in the deep sea. But what happens when you dig below the actively growing surface of the microbial mat, into older, deeper layers of the mat that are cut off from oxygenated water?

Even in the absence of oxygen, microbial life goes on. There may not be any iron-oxidizing Zetas living in the anaerobic (or no-oxygen) zone of the mat, but there are other kinds of microbes in Loihi’s hydrothermal vent communities—some of which don’t need oxygen at all.

Post-docs Joerg Deutzmann and Anne Kaster of Alfred Spormann’s lab at Stanford University are here to search for these anaerobic life forms. They’re working with samples collected where oxygen is absent, as indicated by the electrochemical sensors that we’ve been deploying via the ROV Jason. This usually means that the samples come from the interior of a microbial mat or a hydrothermal venting orifice (below).

An arm of the ROV Jason collecting an anaerobic fluid sample from a deep-sea hydrothermal vent orifice.

Using the ROV Jason to collect an anaerobic fluid sample from a deep-sea hydrothermal venting orifice.

Joerg is interested in isolating anaerobic species that could be used for microbial electrosynthesis. In this process, microbes are “fed” electrons from a cathode. The microbes’ metabolic use of the electrons drives industrially or environmentally relevant chemical reactions—for instance, transforming cancer-causing compounds into harmless substances (i.e., bioremediation), or generating CO2-neutral biofuels.

Joerg is super excited that microbes are growing in one of his tubes.

Joerg is super excited that microbes are growing in one of his tubes.

To isolate the anaerobes, Joerg is using tubes containing different combinations of gases, fluids, and solid substrates that encourage them to grow.

A tube for growing microbes from the anaerobic zone.

A tube for growing microbes from the anaerobic zone, with elemental iron substrate at the bottom.

Anne’s focus is on single cell genomics and metagenomics. Deep-sea anaerobic microbes—which are ancient in origin—share certain genes with land-based microbes used in bioremediation. Anne’s genetic studies of the deep-sea species are aimed at getting a better understanding of how the bioremediators evolved, potentially take us a step closer to being able to engineer them in the future.

What parts of the hydrothermal chemical system are anaerobic microbes using as an energy source? What industrial applications might they have? Do anaerobic microbes exist independently of Zetas, or are there symbiotic relationships among different members of the microbial mat community? The Spormann Lab’s work on this cruise will help to answer these questions, adding a new dimension to our picture of Loihi’s deep-sea microbial ecosystems.

–Cat Wolner, NSF

Photo credits: Cat Wolner (top three); subsurface photo from the Jason control van

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