The Primordial Soup Was Edible
Back in 2005, when I was a first-year microbiology graduate student, I enrolled in a course on bacterial physiology. One of our guest lecturers, Dr. Franklin Harold, was an esteemed researcher in bioenergetics, a field that examines how cells derive and utilize energy. One evening, outside of class, I happened upon Dr. Harold at a seminar, and I asked him a question: "What is your opinion on origin of life research?"
He responded, "It has been an abject failure."
Ten years later, it is still difficult to argue with him. A brief survey of the Wikipedia entry on abiogenesis reveals about 20 different theories and explanations for how non-living matter can evolve into metabolizing lifeforms, ranging from the plausible (RNA World) to the patently ridiculous (panspermia). Put simply, a field with so many different interpretations is wandering lost in the long grass. Any sort of hint at the truth, therefore, is a welcome discovery. Such a hint, albeit a small one, may have been uncovered by new research that has been published in Scientific Reports.
The famous Miller-Urey experiment, which showed that biological molecules can be produced by zapping water and a few gases with electricity, has been debated for some 60 years in regard to just how relevant it is to the origin of life. Yes, some biological molecules can be produced in conditions mimicking (what is thought to be) that of the early Earth, but toxic molecules, such as carbon monoxide and cyanide, are also synthesized. Additionally, it was not even known if the sludge produced by the experiment was capable of supporting life. So, a team of scientists led by Xueshu Xie and Roman Zubarev aimed to find out.
Their first results were not promising. The Miller-Urey goo blocked the growth of E. coli, a rather hardy bacterium. This was apparently due to a toxic cocktail of organic molecules present in the mixture.
So, the authors tried another approach. First, they dried the Miller-Urey gunk to eliminate the toxic, volatile compounds, and then reconstituted it in water. Second, they adapted their E. coli strain to live under harsher conditions. This can be done by growing them in media (liquid food) that the bacteria find unpleasant but tolerable. After three months, the battle-tested bacteria were once again grown in the presence of the poison-free Miller-Urey goo. This time, they did quite well. (See figure.)
Their finding definitely supports the notion that the Miller-Urey gunk can support life. But, there are three major caveats:
First, the researchers still had to add inorganic salts (containing ions such as potassium, magnesium, and calcium) in order for the bacteria to grow. Second, it is debatable whether removing toxic molecules, such as cyanide, is legitimate. Finally, their experiment does nothing to solve the biggest questions of all: How did complex molecules form (e.g., DNA), and how did life evolve?
The answers to those questions remain as murky as the Miller-Urey goo.
Source: Xueshu Xie, Daniel Backman, Albert T. Lebedev, Viatcheslav B. Artaev, Liying Jiang, Leopold L. Ilag & Roman A. Zubarev. "Primordial soup was edible: abiotically produced Miller-Urey mixture supports bacterial growth." Scientific Reports 5, Article number: 14338. Published: 28-Sept-2015. doi:10.1038/srep14338