Mid-Atlantic Ridge 2008

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Cruise Log: August 11, 2008

As you may have read in earlier posts, one very interesting thing about hydrothermal vents is how they sustain so much life. The system is fed by geochemical energy from the vents rather than from sunlight, and organisms at vents are adapted to harnessing that energy. What types of microbial metabolism do we see at vents?  What conditions favor one type of metabolism over another?  Are the microbial communities different between sites and between chimney structures at the same site? What are limiting factors to growth at these sites? These are just a few of the interesting questions we would like to address.

A sulfide chimney from Rainbow showing the chalcopyrite lining in the tube

A flange from Lucky Strike. The high temperature hydrothermal fluid pools underneath this ledge-like structure (near the white areas)
Julie Kirshtein has been using a technique called qPCR to investigate the abundance of microorganisms capable of different kinds of metabolism, such as methanogenesis (making methane), methanotrophy (consuming methane), reverse TCA cycle (a form of CO2 fixation), ammonia oxidation , denitrification (e.g. reducing nitrite) and more. We extract DNA from the sulfide chimneys and target functional genes which code for enzymes involved in these processes. We would like to compare differences between sites and try to relate that back to vent fluid characteristics. So far some of the preliminary results look interesting. For example, we are detecting more methanogens at Rainbow where hydrogen, a substrate necessary for many methanogens, is plentiful. Methanotrophs which consume methane are high at Rainbow and Lucky Strike, where methane is plentiful, but are lower at TAG where methane is very low. We can also look at differences between types of vent sulfides, such as community structure differences between diffuse flow beehive structures as compared to flanges or faster flow chimneys, where conditions may favor one type of metabolism over another, for example sulfate reducers over methanogens.

A beehive structure from TAG. This is more like a spongy textured structure and the fluid diffuses out along the ridges

A very unusual sulfide from Lucky Strike, with yellow elemental sulfur and other minerals
Another way to study microorganisms is to culture them and learn more about their function by studying them in the lab. One of the main goals of this cruise has been to collect active sulfide chimneys from the different vent systems in order to study the distribution and ecology of microorganisms that thrive at high temperatures and low pH (thermoacidophiles). Prior to this cruise, only one thermoacidophile had been described from a vent site in the western Pacific Ocean (Reysenbach et al., 2006). The organism, Aciduliprofundum boonei, belongs to a group of Archaea called the “DHVE2” that has only been detected in deep-sea environments suggesting that it may be endemic to these systems. Over the past month, graduate student, Gilberto Flores, has been trying to isolate more thermoacidophiles using the same conditions that we routinely grow A. boonei with back in Portland. He describes his strategy below:

My initial enrichments (see July 23rd update) seemed promising as I was seeing significant growth in most of the cultures. I eventually diluted a few of these cultures to purity and extracted the DNA so we could verify the presence of the DHVE2. Although I was not positive they were DHVE2 I felt fairly confident because the conditions I was growing them with were fairly stringent and they shared a similar morphology with A. boonei. Well, as it turned out after Julie used QPCR to see what I had in my cultures, these cultures were Archaea but not DHVE2. This puzzled me somewhat so I decided to check the pH of my media as it sometimes rises when I add the various amendments prior to inoculation. I also consulted some preliminary data that Julie Kirshtein had generated on this cruise indicating which sulfide samples had the highest number of the DHVE2. Both of these approaches were fruitful as the pH was in fact too high (pH 4.8-5.0) and I now knew which sulfides to focus my efforts on. To combat the pH problem, I simply added sterile hydrochloric acid (HCl) until the pH was 4.0. I then transferred the existing cultures and inoculated fresh sulfide slurries into this lower pH media. Most of the existing cultures failed to grow at this pH indicating that they were not true thermoacidophiles. On the other hand, a few of the cultures began to thrive. This made us all very excited (well maybe just the microbiologists!!) and so I once again extracted DNA and looked for the presence of the DHVE2. This time, it was confirmed that these cultures contained mostly members of the DHVE2! My next task is to get these cultures pure and continue investigating the metabolism of representative isolates.

Julie and Gilbert discuss qPCR data

Success! A microscope image of the new DHVE2 enrichment culture. Each little blue dot is about 0.8 micrometers (1000 micrometers=1milimeter)

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