Sitting on a laboratory shelf on the third floor of the state-of-the-art Wisconsin Institute of Discovery building are a collection of small vials, each containing a primordial chemical soup. They are all a part of University of Wisconsin botany professor David Baum’s experiment that may change the way scientists study the origin of life.
Though scientists have made considerable inroads in our understanding of molecular biology and genetics, almost no progress has been made in understanding how primordial chemicals on an ancient earth could organize themselves into the genetic molecules DNA and RNA, Baum said.
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The question that has baffled scientists thus far has to do with a phenomenon known as self-propagation, the ability of an organized group of chemicals to reproduce itself. It is essential to life, and so far, no one really knows how such a thing could occur without genetic material, Baum said.
“I think the basic question in the origin of life that we haven’t figured out yet is how systems can become organized and start evolving before they have genetics,” Baum said.
The overarching goal of Baum’s research was not to discover the precursors to genetic material, but to demonstrate one possible approach to study the emergence of self-propagating chemical reactions. Baum’s team began by assuming that self-propagating chemical systems might emerge far more easily than people think.
In addition to self-propagation, the researchers are also interested in the ability of basic entities to become more complex.
Third-year PhD student Lena Vincent assists in Baum’s lab. Vincent discussed the research framework.
“Our framework offers a potential bridge between the non-living world, where you don’t have [self-propagation], to a world in which entities capable of those two things emerge spontaneously in the absence of prior adaptive processes,” Vincent said.
The experimental protocol begins with a collection of vials, each filled with a chemical soup that mimics scientists’ knowledge of the conditions existing on an ancient earth, Baum said. After the vials are sterilized, they sit around for a couple of days before 10% of the content of each vial is transferred to a new vial with a fresh batch of the chemicals.
The researchers then monitor changes in the composition of the vials. This is done over multiple iterations of the procedure, and is compared to vials whose contents have only been diluted once.
“Everything should be the same except that this one has been transferred 12 times in its history, and the other just once in its history,” Baum said, referring to the experimental and control group, respectively. “If history matters, something should be different. If history doesn’t matter, everything should be the same.”
In the experimental group of vials, researchers observed a steady change across generations in certain measured characteristics, Baum said. The measurements mimicked a boom and bust cycle of resource consumption often seen in ecology.
One theory is the dilutions selected for self-propagating chemical networks consumed increasing amounts of resources. Every so often, the population of chemical networks reached a ceiling, leading to a population crash: hence “boom and bust.”
The significance of Baum’s research comes from its methodology, which mimics the evolutionary process of natural selection. The experiment relies on the assumption that only the chemical networks able to propagate faster than they are diluted between generations would survive. While using natural selection is a common practice in biology, Baum believes his is the first group to apply it to non-living or abiotic systems.
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One constant theme throughout the experiment was the challenge presented by the lack of a preexisting framework for the researchers to follow. In developing experimental protocols, the researchers relied heavily on trial and error, UW undergraduate student on the research team Jacob Cosby said.
“We have no prior knowledge of whether anything’s going to work,” Vincent said. “It’s very much an open field. Which means that there’s a lot of room for creativity, a lot of room for different perspectives.”
Baum’s lab employs students from a wide variety of disciplines, including biology, chemistry, physics, math and anthropology, Vincent said.
The researchers, who were funded by the National Science Foundation and NASA, published their findings Oct. 23 in the journal Life.
“NASA has a pretty active exobiology and astrobiology program,” Baum said. “Obviously, if you’re going to go around to other planetary bodies, you want to know what you might encounter, and how might life look if you did run into it.”
Manipulating the experimental conditions and increasing the duration of the experiment are two further avenues the team hopes to pursue, Vincent said. Modifying experimental conditions may provide insight into what conditions are necessary for the formation of lifelike chemical reactions.
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In fact, the conditions in Baum’s test tubes deviate from what would have existed in a primordial earth in one major way, he said; the addition of a chemical compound known as ATP. The compound, which plays an essential role in all biotic reactions, probably did not exist in an early earth.
“Physics will tell us that a system can only self-organize if it has energy,” Baum said. “We took something that we know has high energy that lifelike chemistry can use, but of course, probably wasn’t present on the early earth. If we confirm that we have this lifelike behavior using ATP, then it’s relatively easy to take the ATP out and see if we can get this behavior with more realistic compounds.”
Researchers expect to see an increase in the complexity of the lifelike chemical reactions as they increase the duration of the experiment, Vincent said.
The current experiment spanned the course of 40 generations of vials and was performed entirely by hand. Researchers are looking into automating some aspects of the experimental procedure in order to scale up, Vincent added.
“Our immediate goal is to demonstrate that these self-propagating systems we think we’ve found can evolve,” Vincent said. “But in order to do that, we have to observe them over a longer period of time.”