Team:Heidelberg/Team/Gallery

The quest for a magical substance to generate gold from inferior metals stirred the imagination of generations. However, this substance, the Philosopher’s Stone, stands for more than just the desire to produce gold. In the old days, the fabled Philosopher’s Stone also represented wisdom, rejuvenation and health. Nowadays, gold is still of great importance for us as it is needed for most of our electronic devices.

In 2007, more than two tons of gold were discarded hidden in electronic waste in Germany. Most of the precious element end up on waste disposal sites as only a minor fraction of 28 % of the gold is recycled also due to the small amounts per devide. Since our planet’s gold supplies are limited, the metal is more and more depleted and the value of gold continously reaches all-time highs. In order to satisfy our society’s need for gold, we have to develop heavy mining techniques involving strong acids, causing devastating impact on human and environment [1] [2] [3].

Besides economical usage of the resource gold, one way to reduce global demands for gold is elevation of gold recovery [4]. Intriguingly, nature itself offers a structure that has been reported to efficiently extract pure gold from solutions containing gold ions. This fascinating molecule is called Delftibactin and is in fact a small peptide secreted by a metal-tolerant bacterium called Delftia acidovorans.

This extremophile has the incredible ability to withstand toxic amounts of gold ions in contaminated soil . What is the special feature of Delftibactin enabling precipitation of gold that efficiently? If one could culture these bacteria and produce Delftibactin in large scales, could one potentially recover gold from electronic waste in a cost- and energy-efficient way? But what is the special feature of Delfibactin to precipitate gold that efficiently?

Delftibactin is no ordinary peptide but a non-ribosomal peptide (NRP) [5] [6]. The efficient and non-polutative large-scale production of this NRP in E. coli could revolutionize the recovery of gold from electronic waste and additionally highlight the plethora of versatile applications for non-ribosomal peptide synthetases (NRPSs). The most sriking feature of these non-ribosomal synthetases is their ablity to incorporate far more than the 21 common amino acids into peptides. They make use of numerous modified and even non-proteinogenic amino acids [7] to assembly peptides of diverse functions.

Delftibactin is a NRP produced by a hybrid NRPS/ polyketide synthase (PKS) system. In their recent publication, Johnston et al. [5] predicted that the enzymes responsible for producing delftibactin are encoded on a single gene cluster, hereafter referred to as Del cluster. It comprises 59 kbp encoding for 21 genes. DelE, DelF, DelG and DelH constitute the hybrid NRPS/ PKS system producing delftibactin, with DelE, DelG and DelH being NRPS and DelF the PKS. The remaining enzymes involved in the Delftibactin synthesis pathway are required for NPRS/ PKS maturation or post-synthesis modification of Delftibactin. The predicted activities of the assumed proteins are:

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