金の新たな側面
Hello everyone, SCIENSPOT is a podcast that shines a spotlight on the latest scientific
technology from Japan. Your host is REN from SCIEN-TALK. Today I am going to talk about
From Toxin to Gold Treasure. When you hear the word gold, what comes to mind?
Perhaps valuable metal, a symbol of wealth, or maybe ancient tales of alchemy.
Gold is used in many aspects of our lives. But did you know that the gold
we usually see has a lesser-known, slightly darker side? Today's story is about this hidden
aspect of gold and the amazing microorganisms that interact with it. The gold we are familiar
with is elemental gold, the metallic state. It is very stable and non-toxic. However,
in certain environments, such as underground, gold can exist in the form of gold ions.
Specifically, trivalent gold ions are soluble in water and are actually toxic to living organisms.
Similarly to heavy metals like mercury or lead, they can damage cells and hinder life processes.
Imagine if you had to survive in a toxic environment, what would you do? To stay alive,
you would need to neutralize the toxins or transform them into something harmless.
The research we are discussing today focuses on a microorganism that lives in precisely such a
harsh environment, the surface of gold nuggets, where toxic gold ions are abundant. This clever
Delphitebactin Aの発見と研究
bacterium, named Delphitea asciudivorans, produces a special natural product called
Delphitebactin A, and this molecule can rapidly reduce toxic gold ions into non-toxic elemental
gold in the form of nanoparticles. It's like a tiny biological superhero that cleans up
toxic waste and turns it into valuable gold treasure. Delphitebactin A has garnered
significant interest from many researchers since it was first reported in 2013 as a biodegradable
molecule that forms gold nanoparticles. However, its complete chemical structure,
especially its full 3D shape and the detailed mechanism of how it reduces gold ions,
has remained a mystery for 12 years. Challenging this long-standing mystery was a joint research
then led by a professor at the Tokyo University of Agriculture and Technology.
For the first time in the world, they have now fully elucidated the complete structure of
Delphitebactin A and its astonishing gold ion reduction mechanism.
So how did they unravel this mystery? The key was low synthesis and comparison.
First, the research team established a new methodology for efficiently chemically
synthesizing Delphitebactin A. Think of it like assembling a complex, a giant Lego set.
They combined solid-phase synthesis, which allows for rapid linking of units like
Delphitebactin Aの構造解析
building of Lego blocks, with trace-free styrofoam ligation, a special chemical glue
used to construct unsaturated amino acid units. This new technique enables them to
successfully synthesize all 16 possible diastereomers that is all 16 different 3D
versions that Delphitebactin A could potentially have. With all 16 versions in hand, the puzzle
solving began in earnest. This team meticulously compared the structural data of these artificially
synthesized 16 Delphitebactin A versions with the data from Delphitebactin A produced naturally by
bacteria. As a result, the complete chemical structure of natural Delphitebactin A was finally
determined for the first time in the world, fitting together like perfectly matched puzzle pieces.
Once the structure was known, the next step was to elucidate its function. How does it reduce gold
ions? It is known that Delphitebactin A contains four amino acids that could potentially bind to
metal ions. However, typically only two are necessary for gold ion binding, so the researchers
sought to identify which specific parts were truly involved in gold ion reduction by comparing
the gold ion reduction rates of each of the 16 synthesized diastereomers. To their amazement,
it became clear that natural Delphitebactin A reduced gold ions significantly faster than
Delphitebactin Aの驚異的な能力
any of other versions. This strongly suggests that through an incredibly long process of evolution,
the bacterium has optimized this molecule specifically for gold ion reduction.
Further detailed analysis reveals that two specific amino acids are deeply involved in this reduction
reaction. And by analyzing the chemical products formed when gold ions and Delphitebactin A were
mixed, they discovered for the first time in the world that the FH-ornitin-6 amino acid gets
oxidized and in turn, the toxic gold ions are reduced, ultimately forming harmless elemental
gold nanoparticles. This research represents a truly groundbreaking discovery, as it has
for the first time fully clarified the fundamental basis of Delphitebactin A's
remarkable ability to reduce gold ions. This study is fascinating from the perspective of
natural nature's ingenious chemistry. Beyond satisfying scientific curiosity,
this discovery holds significant potential for our society. For example, it is expected to provide
a new technological foundation for efficiently removing toxic gold ions from environmental
sources, such as industrial wastewater, or for precisely forming gold nanoparticles with specific
shapes. Gold nanoparticles are crucial materials used in a wide range of fields, including medical
diagnostics, therapeutics, electronics, and catalysis, so their application possibilities
are immense. So that's all for today's SciencePod, and I'm sorry for the late update of this episode, I
have to rest yesterday, because as I mentioned, I traveled to the Cold War in the UK, so I
took some vacations, so I was not able to update this podcast, but I now still continue.
So this podcast is broadcasted every on weekday morning in both Japanese and English,
I'd love for you to listen to the podcast and post your notes and thoughts with the hashtag
SciencePod. See you next time.
