Biologists from Konstanz have discovered a unique and ancient bacterial metabolism based on phosphorus. Four elements are at the heart of this discovery: an analytical calculation dating back to the 1980s, a modern sewage treatment plant, the identification of a new bacterial species, and an artifact dating back approximately 2.5 billion years.

Our story begins with a piece of paper in the late 1980s. On this page, the scientist calculated that converting the chemical compound phosphite into phosphate would release enough energy to produce the ATP molecule, the cell’s energy carrier. Therefore, the microorganism must be able to provide itself with energy. Unlike most living organisms on our planet, this organism will not rely on light or the decomposition of organic matter as its energy source.

The scientist actually managed to isolate such a microorganism from the environment. Energy metabolism is based on the oxidation of phosphite to phosphate, as predicted in the calculation. So how exactly does the biochemical mechanism work? Unfortunately, the key enzyme needed to understand the biochemistry of the process remained secret, and so the mystery remained unsolved for many years. Over the next three decades the page was put in the drawer, the research approach relegated to the background. However, the scientist could not get this thought out of his mind.

The scientist is Bernhard Schink, professor at the Institute of Limnology at the University of Konstanz. 30 years after doing the calculation on paper, the unexpected discovery was again demoralizing.

What he had been thinking about for years was finally found: in the sewage plant in Konstanz, just a few kilometers from Bernhard Schink’s laboratory. Zhuqing Mao, a PhD student in biology from Konstanz, examined a sample of sewage sludge and discovered a second microorganism that also extracts energy from phosphide. Konstanz biologists, led by Bernhard Schink, placed this bacterium in an environment where its food source was only phosphite. And indeed the bacterial population was increasing.

“This bacterium lives by phosphite oxidation and, as far as we know, only by this reaction. Thanks to this, it carries out energy metabolism and can also create its cellular substance from CO2. _{2,” Shink explains.} “This bacterium is an autotrophic organism, just like a plant. However, it does not need light like a plant because it gets its energy from the oxidation of phosphite.” Surprisingly, it turned out that the bacterium was not only a new species, but also a completely new type of bacteria.

Tracing the molecular mechanism

From then on, everything happened very quickly. A network of Konstanz researchers, including Bernhard Schink, Nikolai Müller, David Schlehek, Jennifer Fleming and Olga Mayans, dedicated themselves to solving the mystery. They grew a pure culture of this new bacterial species and eventually managed to identify the key enzyme that triggers the oxidation of phosphite to phosphate.

“This discovery came from Nicolaus Müller and his experiments with enzymes,” says David Schleheck. Nicolas Müller was able to clearly demonstrate the activity of the enzyme and thus reveal the biochemical mechanism of the key enzyme. Olga Mayans and Jennifer Fleming created a three-dimensional model of the enzyme structure and active site to understand the reaction pathway.

“What was very surprising was that during oxidation, the phosphite binds directly to the precursor of the energy carrier AMP, thus creating the energy carrier ADP. In the next reaction, two of the ADPs formed are converted into a single ATP, and thus the organism ultimately lives.” Nikolai Muller summarizes the path of the reaction.

Eventually it all came together: The original page turned into a pile of papers, resulting in a publication in the scientific journal PNAS.

A remnant from 2.5 billion years ago

The discovery of a new type of energy exchange is in itself a great scientific achievement. However, the research team believes that this type of metabolism is not new at all, but very old, about 2.5 billion years old.

“It is assumed that at the beginning of evolution, when the Earth cooled, phosphorus was still largely in a partially reduced form and was only gradually oxidized later. The metabolism we have now discovered fits very well with the early phase of the evolution of microorganisms,” explains Bernhard Schink.

Therefore, the biochemical mechanism that bacteria use for their metabolism is not new, but has most likely been preserved from the earliest times of our planet: when life appeared on our planet and the first microorganisms fed on inorganic compounds such as phosphite. Thus, new scientific discoveries provide clues to early biochemical evolution on our planet. They also provide a clue to the biochemical machinery that makes life possible in very hostile places, perhaps even on alien planets.