CHAPTER 20: Gold

There is growing evidence that an active biogeochemical cycle for gold (Au) exists, and that this process is responsible for the solubilization and dissemination of gold throughout the environment. It has been shown that soluble gold, in its ionic forms or in complexes, can enter cells by non-specific intake and that it accumulates in plants, fungi and fish. Recent observations have demonstrated the presence of bacterial biofilms on gold nuggets and that these can contribute to its mobilization in the environment. Bacteria such as Salmonella enterica and Cupriavidus metallidurans use Au-specific transcriptional regulators that detect its presence and control the expression of specific resistance factors. Their presence allows these microorganisms to cope with the toxic effects of gold ions. This chapter will address the biological influence of the cycling of gold, focusing primarily on the current understanding of the regulatory proteins involved in its detection and the induced mechanisms that alleviate toxicity in bacteria caused by Au. In addition, gold has been used in medicine from ancient times. Before the discovery of antibiotics and because of its toxicity, gold was used to treat infections and a number of diseases. Currently, Au(I) and Au(III) compounds are being designed for treatment of cancers, rheumatoid arthritis and viral and parasitic diseases.