Unlocking the Mysteries of the Microbes

By Dr. Jennifer Glass and Matt Barr

Now that we’ve laid a foundation for microbial activity early in Earth’s history, we will start discussing some of the exciting research going on at Georgia Tech in the School of Earth and Atmospheric Sciences (EAS).

For over three-fourths of Earth’s history, its ocean chemistry was vastly different than it is today. Instead of today’s “anemic” (iron-starved) oceans, the ancient oceans were “ferruginous”, containing low oxygen and abundant iron. By studying modern ecosystems that still retain ferruginous habitats, “geobiologists” at GT EAS and around the world are probing questions about how microbial life flourished and changed the face of the early Earth.

Dr. Jennifer Glass’ research group is at the forefront of studying interactions between microbes, iron and greenhouse gases. In addition to carbon dioxide, two other important greenhouse gases are methane and nitrous oxide, both of which likely warmed our planet enough to enable the persistence of liquid water and evolution of early life billions of years ago, despite the faint young sun paradox discussed in our previous post.

The Glass lab is studying greenhouse gas cycling via microbial and abiotic redox reactions, which move electrons between chemicals towards a state of lower free energy, and are crucial for all life. These redox reactions are also key to nutrient cycles that move bioessential elements like carbon, nitrogen and iron through planetary ecosystems. Half the lab works on methane, and the other half on nitrous oxide, with iron as a common theme connecting the two.

Methane is the second most abundant greenhouse gas on modern Earth and may have been even more important in our planet’s past. With funding from NASA’s Exobiology and Evolutionary Biology Program, the Glass lab and its collaborators are testing the hypothesis that iron and methane contributed to early metabolic processes of primitive – yet completely unknown – microbes that likely still exist today in ferruginous ecosystems. These microbes might “breathe” iron and “eat” methane to obtain energy and food.

Lake Matano in Indonesia is one of the best analogs that exists today of ferruginous oceans that existed in the Archean Eon. While most lakes turn over at least once a year, Lake Matano’s deep waters are too dense to mix with its surface waters. This means that the mud at the bottom of Lake Matano is completely shielded from atmospheric oxygen and is constantly bathed with iron from mineral-rich soils flanking the lake. Consequently, it may harbor microbial communities similar to those in the Archean oceans. Collaborator Dr. Sean Crowe of the University of British Columbia, an adjunct professor in EAS, has provided the Glass lab with sediment samples from a variety of depths in this ecosystem.

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Lake Matano lies on the Indonesian island of Sulawesi. Its waters are uniquely characteristic of the Archaean oceans that are key to unlocking the secrets of early life on Earth.

Glass lab PhD candidate Marcus Bray and postdoc Dr. Nadia Szeinbaum are cultivating microbes from these precious sediments to decipher how their ancient relatives were able to grow without oxygen in Earth’s deep past. They exposed these microbes to metal-rich minerals and methane and then waited patiently while both substrates were slowly transformed. They’ve also teamed up with the lab of Dr. Frank Stewart (GT Biology) to sequence the microbes’ DNA to study how the microbial population has changed over time. The longest enrichments have been running for over two and a half years, and certain microbial groups that started off as minor players are now dominating. Ongoing work aims to show precisely how these microbes are thriving off of methane and metals. By understanding the influence of iron on methane, and vice versa, the mechanisms controlling methane flux to Earth’s atmosphere can be better resolved, both in the modern and the Archean eras. This research could simultaneously unlock ancient mysteries and potentially provide solutions for a greener future.

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Sediments from Lake Matano must be carefully stored in conditions that won’t expose them to the oxygen outside. These sediments are used to grow microbes whose chemistry is studied intently. They reside in a special refrigeration unit in Dr. Glass’ lab at Georgia Tech.

I caught up with Chloe Stanton, an undergraduate EAS major who has worked in the Glass lab since her first semester on campus, to learn more about another project, funded by the NASA Astrobiology Institute’s “Alternative Earths” team. Chloe, EAS PhD candidate Amanda Cavazos, and Dr. Glass are investigating the production of nitrous oxide (also known as “Laughing Gas”) via chemical interactions between iron and reactive nitrogen-containing molecules. Chloe showed me how she carefully concocts small batches of the poisonous gas nitric oxide in a chemical fume hood and makes artificial iron-free seawater from scratch by dissolving individual salts in pure water. She then measures rates of nitrous oxide production from these primitive substrates in an anoxic chamber that mimics the Earth’s ancient oxygen-free atmosphere, with the goal of determining how fast these reactions occurred in the “middle Earth”, or Proterozoic Eon.

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Undergraduate researcher Chloe Stanton prepares a sample for study in the Glass Lab’s anoxic chamber.

These two research projects underway in the Glass lab open up some intriguing possibilities. Aside from giving us a better understanding of how the Earth has stayed habitable for microbes over billions of years, this research might be useful to environmental engineering efforts that employ microbes to treat waste water and cut greenhouse gas emissions. Also, the very existence of these microbes greatly broadens the spectrum of conditions under which we know life can develop. Unique assemblages of gas molecules could even be used as “biosignatures” for life on exoplanets outside of our solar system, with significant implications for astrobiology’s search for life elsewhere in the cosmos and new exploration avenues in future space missions.

Thanks for reading, and stay tuned for next week’s journey into science at GT EAS!

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Microbes in Wonderland

By Matt Barr

Our expansive journey into the heart of science begins with the story of the hardy microbe.  A single-celled organism that has made its home quite literally everywhere, we are only beginning to discover the fascinating past and potentially revolutionary future that these microscopic organisms share with us.

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Microbes be microbin’.  These microbes were found in NASA spacecraft assembly areas – some of the cleanest places on Earth.  Source: NASA JPL.

Microbes can be found everywhere, from the harshest environments to the most sterile.  First discovered in the 1600’s, little information was known about how they actually operated until the late 19th century.  Even then, most of our detailed observations of microbial activity did not occur until the second half of the 20th century.  However, once it was understood that microbes inhabit virtually any space where liquid water exists, a new view of life on Earth emerged and opened the door to exciting discoveries in a field of science that has only recently been explored more deeply.

Before delving into the specifics of our research at Georgia Tech, it’s a good idea to establish a context in which the research is being conducted.  That involves explaining where the microbes have been, where they’re going, and how they’re taking us along on their path through history.

A long time ago in a galaxy very, very close by (our own, in fact), the earth looked nothing like it does today.  The land masses we’ve come to know and love, the oxygen that our bodies enjoy breathing on a pleasant spring day (and all of the other days), the warmth of a sun whose luminosity and energy output that allow for those pleasant spring days – all were nowhere to be seen.  Indeed, there were no eyes as we know them with which to see, even if all those lovely life-sustaining conditions were, in fact, anywhere to be seen.

And yet, to quote those immortal words of Jurassic Park’s Dr. Ian Malcolm, “life, uh, finds a way.”

What life though?  Under the harsh conditions that would have burned your lungs, drowned you, choked you to death, or finished you off in any number of other nasty ways, there was a class of life that defied all the odds stacked against it.  We’re talking, of course, about our dear, omnipresent friends known as microbes.

For the first billion or so years of Earth’s history after its accretion (that is, after Earth finished forming into a planet by combining bigger and bigger chunks of rocks, debris, gases, and other materials swirling around our sun in its orbital path), no life seems to have existed.  Indeed, it seems that there was little more than one big ocean and an atmosphere on our planet.  At this magic billion-year mark, however, evidence of the first single-celled organisms begin appearing in the geologic records.  The fascinating aspect of this appearance (one of many) is that our understanding of the conditions under which it’s possible for life to form and sustain itself were very much counter to the conditions present on our planet and in our solar system so long, long, long, long ago.

For starters, we’re fairly certain that a phenomenon referred to as the “faint young sun” was in place.  The faint young sun was precisely that: a star that wasn’t hot enough to warm our planet to a temperature that supported liquid water.  This is a critical piece of information because without liquid water, life as we know it cannot exist.

As the life of a star progresses, it undergoes a process known as the Main Sequence, during which the hydrogen at its core burns at such high temperatures that the hydrogen atoms fuse together to create the next heavier element, helium.

As this process takes place, the star grows hotter and brighter.  However, in what we call the Archaean Eon, that period between 2.5 – 4 billion years ago, our sun’s luminosity and its corresponding energy output were about 70% of what they are today – amounts insufficient to support life.  Yet, the evidence of life is found in our rocks that date from the very Archaean Eon when life was not supposed to exist.  What gives?  What GIVES?!

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During the Archaean Eon, our sun was only about 70% as hot and bright as it is today. Following along with the Main Sequence illustrated above, these conditions correspond to a sun that is closer to the blue end. Source: Study.com

It turns out that, thanks to the relatively consistent violent explosions via those angry mountains that we call volcanoes – spewing their lava, ash, and general mayhem, a fairly reasonable (though not entirely accepted!) explanation neatly presents itself.  This is where we need to introduce greenhouse gases like carbon dioxide, methane, water vapor, and nitrous oxide into the conversation.  Some of the most important substances expelled into the atmosphere by volcanoes are, in fact, those infamous greenhouse gases we keep hearing about.  The thing about greenhouse gases is that in certain amounts, they can be very beneficial.  In this case, they appear to have benefited our early earth by keeping it warm enough to host liquid water when the faint young sun wasn’t pulling its weight.

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An illustration of greenhouse gas emissions produced by volcanoes. Imagine this process going on at much greater magnitudes and frequencies all over the planet to get an idea of what the Archaean Earth would have been like. These gases likely warmed the planet enough to sustain liquid water, the key ingredient for life as we know it. Source: Wikimedia.org

When we take into consideration that faint young sun, the lack of readily available oxygen in the early atmosphere, and the abundance of these greenhouse gases, our ideas about the development of life on Earth are pushed in a new direction.  The great Carl Sagan was one of the first scientists to suggest that it was these greenhouse gases which warmed the planet enough to allow water to exist as a liquid.  This, in turn, allowed for the earliest life forms to arise much farther back in time than seems plausible, and ultimately develop into the microbes that may have built up our atmosphere into a sort of blanket of habitability through their metabolic processes.

One final component of our microbe picture is that during their metabolism, they can both consume and produce greenhouse gases.  For example, in the presence of iron and methane, a microbe can consume methane and transform it into carbon dioxide.  The way it does this is by interacting with iron and trace metals through something called redox chemistry.  Redox chemistry involves the transfer of electrons between molecules of opposite electrical charges, and can get rather complicated.  For a better idea of how redox chemistry works, check out this site from Washington University.

What’s important to take away from this process is that it can occur without oxygen, which essentially excludes the catalogue of complex life (life that is composed of more than one cell, to be exact) from using it as a way to derive energy.  A deficiency of oxygen is exactly what characterized the Archaean atmosphere.  With liquid water present in abundant amounts due to the warming greenhouse gases being pumped into the atmosphere from volcanic and microbial activity, more and more microbial life could begin to flourish and ultimately begin increasing the oxygen content of the atmosphere.  Gaseous oxygen emitted into the atmosphere is another result of microbial metabolism, and it’s in this way that microbes ultimately paved the way for complex life on our planet to develop.

This interaction with and, specifically, consumption of greenhouse gases also means that microbes are promising partners in the future of environmental engineering processes.  They can clean up wastewater, help us reduce our currently excessive greenhouse gases, and move us in the direction of a cleaner, greener planet.  That is, if we can determine exactly how they work their magic and exactly which microbes are responsible for which chemical processes.

This brings us to the exciting research being conducted in Dr. Jennifer Glass’ lab by her and her students.  Stay tuned for more details and check out Dr. Glass’ website and blog for more in-depth information at jenniferglass.com.

In the Beginning…

Welcome to the official blog of Georgia Tech’s School of Earth and Atmospheric Sciences! We’re hoping to be up and running at full steam by the end of this summer. Check back here regularly to find out about all the exciting research being done by our faculty and students. From exploring the depths of our oceans to uncover the unexpected ways in which climate change is affecting our planet, to focusing our sights towards Mars and beyond where the origins and future of our species may lie, we leave no scientific stone unturned in our search for answers to the questions that drive us.

Stay tuned for a helluva story!