Bacteria produce gold by digesting toxic metals

Bacteria produce gold by digesting toxic metals High concentrations of heavy metals like copper and gold are found to be toxic for most of the organisms. But scientists have discovered a modern alchemist that can extract valuable trace elements from a compound of toxic metals without poisoning itself. One of the interesting side effects is the production of gold nuggets. This microbial magician, C. metallidurans, when placed in a minilab full of gold chloride converts it to 24-carat gold in a week’s time, a process that this bacterium is thought to carry out regularly in nature. This finding by Kazem Kashefi and Adam Brown has been exhibited as an art instalment called â€Å"The Great Work of the Metal Lover†. The art work consists of a portable lab which consists of a glass bioreactor containing the bacteria. While Kashefi calls this as microbial alchemy, Brown calls it as neo-alchemy which is a cross between modern microbiology and alchemy. This artwork received an honourable, mentioned in the world renowned cyber art competition, Prix Ars Electronica, held in Austria. Producing pure gold from bacterium seems to be a boon at a time when the price of gold has reached an all-time high. But, does this mean that the scientists have got the answer to the international debt crises? Although this bacterium can produce the 24-carat pure gold, but it has been said that it will be cost prohibitive to carry out this experiment at a larger scale. So, one should not see this as a golden investment in economic crisis. But, this discovery has surely created a debate over the use of science and technology, the greed and other economic and environmental impacts associated with it. This work can be used to address questions regarding the ethics related to science and the magnificent engineering of nature. When discovered, the bacterium was initially found to be resistant to cadmium but subsequent studies identified that this strain is multi-metal resistant and has two plasmids pMOL28 and pMOL30 which harbour multiple loci for metal resistance. The bacterium’s ability to thrive in toxic environments with a high number of heavy metal resistant genes makes it an excellent model organism to study the means by which microbes deal with heavy metal stress. Such unique ability of this extremophile to metabolize toxic substances might also provide an insight into understanding the origin of life. When too much copper has accumulated inside the bacteria, it is normally pumped out by the enzyme CupA. However, when gold compounds are also present, the enzyme is suppressed and the toxic copper and gold compounds remain inside the cell. Copper and gold combined are actually more toxic than when they appear on their own, says Dietrich H. Nies. To solve this problem, the bacteria activate another enzyme CopA. This enzyme transforms the copper and gold compounds into their originally difficult to absorb forms. This assures that fewer copper and gold compounds enter the cellular interior. The bacterium is poisoned less and the enzyme that pumps out the copper can dispose of the excess copper unimpeded. Another consequence is that the gold compounds that are difficult to absorb transform in the outer area of the cell into harmless gold nuggets only a few nanometres in size, says Nies. In nature, C. metallidurans plays a key role in the formation of so-called secondary gold, which emerges following the breakdown of primary, geologically created, ancient gold ores. It transforms the toxic gold particles formed by the weathering process into harmless gold particles, thereby producing gold nuggets. The study conducted by the joint German-Australian research team provides important insights into the second half of the bio-geochemical gold cycle. Here primary gold metal is transformed by other bacteria into mobile, toxic gold compounds, which is transformed back into secondary metallic gold in the second half of the cycle. Once the entire cycle is understood, gold can also be produced from ores containing only a small percentage of gold without requiring toxic mercury bonds as was previously the case.