Nowadays, platinum ressources are an issue because of their planned disappearance toward 2064. Moreover, any alternative has been found so far to counteract the disparition of this metal compared to its central importance in many industries (electronic, automobile, medecine..) .

Accumulation of the metal on the road side has been frequently shown since the beggining of the 21th. Futhermore, alternatives methods to recycle precious metal are investigated. Here, we use the adsorption potentiel of bacterial natural componants (specifically flagellum and biopeptides) to make a process ables to extract or concentrate the platinum available on different compartiments like soil, plants, sewege sludge...  

[[File:T--Aix-Marseille--maquette2.jpeg|770px|center|thumb|Maquette of our process in the futur : Process has been imagined in a circular platinum economy based on the sludge treatment. Platinum found on the <u>water retention bassin</u> is recovered and incinerated. Though, valuable ashes obtained would be treated by both steps we made : the first one is a siderophore treatment making a first concentration of the platinum and other metals, the second one is a flagellin treatment allowing to make industrialisable platinum. In consequence, treated sludge are depolluted from metal and can be spreaded on the crops making an additional valorization. The recycled platinum cans be used in automobile industry for example and be an element of new automobiles. And steps finally come a full circle. ]]

Since a law from 1993, platinum is largely used in catalytic converter to avoid toxic gaz release <ref>J. de Aberasturi, et al., Minerals Engineering 24, 505 (2011)</ref>. . During the automobile fonctionnement, the precious metal is rejected and deposed on the road under a ionic form <ref>P.S Hooda & al. 2007, https://www.ncbi.nlm.nih.gov/pubmed/17604084</ref><ref>Liliane Michel Legret & al. http://link.springer.com/article/10.1007/s11368-012-0491-3.</ref> Platinum leaching makes an accumulation of this metal on the road side. By default, it has been prooved that plants are potentiel bioaccumulator of platinum, which is found concentrated on the roots, leaves.. Otherwise, the metal is also carried on the sewage sludge and is actually an issue regarding the recycling potential of these sludge.

In the previous article <ref> Improving recoveries of platinum and palladium from oxidized Platinum-group element ores of the Great Dyke, Zimbabwe, using the biogenic siderophore Desferrioxamine B, Dennis Kraemer & al. </ref>, authors made bioleaching with synthetised siderophores. By this way, they extracted approximately 80% of the total platinum found in the ore. But we were looking for a synthetic biological approach.  

Previous work showed that siderophore which are molecule secreted by bacteria to catch iron are able to catch other metals by default. Specifically, many articles showed a high affinity of Desferrioxamine B ( produce by ''Streptomyces coelicolor'') for tetravalent metal ions and more specifically platinum. These results encouraged us to make a biobrick coding the sequence corresponding to the 4 enzymes involved on the metabolic pathway of Desferrioxamine B. <i>E. coli</i> was used to produce this biobrick. Produce a gram positive bacteria pathway in a gram negative bacteria is restrictive <ref> Wandersman & Delepaire https://www.ncbi.nlm.nih.gov/pubmed/15487950  </ref> , considering the risk of toxicity for the conductress bacteria. To counter this potential issue, we regulate trasnscription using the control of an inductible promotor (pBAD/araC).

It has to be noted that the siderophore here is specific for platinum but the same cloning could be performed with siderophore specific for others metals, thus the potential of our process to be applied in the recovery of others metals.

1. Transformation of E.Coli with an inductible plasmide holding the ''des'' cluster

2. Induction and production of the desferrioxamine B

Then, the produced siderophore would be purified and transfered in the recuperation solution containing the platinum and other metals. Therefore, those metals must be recruit by our purified siderophores. Though those siderophores would be import using a sowing of ''Streptomyces coelicolor''. Then simple centrifugation and combustion will concentrate the solution in metal a first time.

It was shown that proteins are able to bind platinium and especially bacterial flagellums which are naturally a high platinum adsober <ref>Capeness & al. 2015, http://eprints.nottingham.ac.uk/27979/1/Michael%20Capeness%20-%20Thesis%20-%20PDF.pdf</ref><ref>Deplanche & al., 2007 http://onlinelibrary.wiley.com/doi/10.1002/bit.21688/abstract. </ref> Furthermore, many peptides were generated based on sequences selected by phage display in order to enhance metal ions adsorption including gold, silver platinum and a plenty of other metals, hence the potential of our process to be performed with other metals.<ref>Uratu Ozgur Safak Seker & al., 2011, http://www.mdpi.com/1420-3049/16/2/1426.</ref>

* the ambient reducer power reduces ions into oxidized nano particles

All together, these findings incite us to use these natural properties to build a biobricks which is a high affinity binder of platinum based on <i>E. coli</i> and <i>Desulfovibrio vulgaris</i> flagellum and synthetic peptides sequences. To this end, we analyze the flagella sequence and structural proprieties of the external part of the flagella. Then, on the part of the flagellin faced to the external medium, an insertion restriction site will be inserted. Then specific precious metal peptides would be added using this insertion site to increase the level of adsorption specificity and yield. In this way, peptide would be faced to the external medium and able to bind metallic ions. To obtain a high transcription level of this sequence, we put transcription control under a strong promotor enabling a high flagellin production.

Next, the flagellin produced will be added to the first concentrated platinum solution. Flagellin containing specific peptides will bind the free or available ions of the medium and reduce them into oxydised nanoparticules usable in industry. A simple centrifugation of the flagellin binding to the platinum allow to concentrate the metal a second time.