Design and construction of gold-selective bacterial biosensors

CERMINATI, S.; SONCINI, F. C.; CHECA, S. K.

San Miguel de Tucumán

Congreso; VII Congreso Argentino de Microbiología General SAMIGE del Bicentenario; 2011

Sociedad Argentina de Microbiología General

Mención Especial a la Comunicación Oral - Gold (Au) is continuously demanded both as a valuable commodity and by modern industry because of its unique physicochemical properties that make it appropriate for many applications. Most analytical methods used to evaluate Au content in economically suitable deposits require sophisticated instrumentation and trained personnel. The use of whole-cell bacterial biosensors has emerged as a simple and cost-effective alternative to conventional detection procedures for several metals, including copper (Cu). However, these bioreporters are usually not selective enough and detect a group of chemically related metals. In this study, we developed whole-cell bacterial sensors that selectively detect Au ions. These sensors are based on the regulatory unit controlling resistance to this toxic metal in Salmonella enterica serovar Typhimurium. In the biosensor, expression of the gfp reporter gene is directed by the  Salmonella golB promoter which is transcriptionally controlled by GolS. The sensor/regulatory protein distinguishes Au(I) from either Cu(I) or Ag(I) ions, which differentiate it from other monovalent metal sensors such as CueR that binds the three metals with similar affinity. In order to be used as a biotechnological tool, we introduced the Salmonella gol locus in the chromosome of a non-pathogenic Escherichia coli strain. The designed bacterial sensor exhibits low background fluorescence, high signal-to-noise ratio, and improved sensitivity for detecting Au ions in a wide range of concentrations (from 5 to 470 nM) with an estimated detection limit of ~33 nM, equivalent to ~ 6 µg l-1 (or parts per billion) Au(I). Due to the intrinsic characteristics of the regulatory protein, the fluorescent Au-biosensor exhibited also minimal interference by chemically related metals such as Cu or Ag that are commonly found associated with Au in deposits. These highly specific and sensitive Au detectors will allow the development of rapid and robust screening tools to improve discovery and extraction procedures for this precious metal.