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J. Gen. Appl. Microbiol., 50, 221–228 (2004)

Full Paper Biosorption and recycling of gold using various microorganisms
Takehiko Tsuruta
Department of Applied Chemistry, Tohwa University, Fukuoka 815–8510, Japan (Received November 13, 2003; Accepted July 29, 2004)

In order to obtain basic information on the biosorption and recycling of gold from aqueous systems using microbial cells, thebiosorption of gold by various microorganisms was investigated. Of 75 strains of microorganisms tested (25 bacteria, 19 actinomycetes, 17 fungi and 14 yeasts), high abilities of gold biosorption from a solution containing hydrogen tetrachloroaurate (III) were found in some gram-negative bacterial strains, such as Acinetobacter calcoaceticus, Erwinia herbicola, Pseudomonas aeruginosa, and P.maltophilia. Most of the gram-positive bacteria, actinomycetes, fungi and yeasts had a lower ability for gold biosorption than gram-negative bacteria. On the other hand, all of the microorganisms tested adsorbed far smaller amounts of gold from a solution containing gold dicyanoaurate (I). The biosorption of gold from a solution containing hydrogen tetrachloroaurate (III) using P. maltophilia having ahigh adsorbing ability for gold was very rapid and was affected by the pH of the solution, external gold concentration, and cell amounts. P. maltophilia cells immobilized with polyacrylamide gel also have a high ability for gold biosorption. The gold adsorbed on the immobilized cells is easily desorbed with 0.1 M thiourea solution. The immobilized P. maltophilia cells can be used repeatedly inbiosorptiondesorption cycles. Key Words——gold biosorption; gold desorption; gram-negative bacteria; immobilization; Pseudomonas maltophilia

Introduction

The demand for gold has increased markedly because of its increasing use in the electrical industry and the development of drugs containing gold. Therefore, the recycling of this valuable resource has become a subject of wide interest. Recently,some researchers have investigated the recovery of gold using microbial cells, such as fungi (Gomes et al., 1998; Matsumoto and Nishimura, 1992; Pethkar and Paknikar, 1998), yeasts (Karamuchka and
* Address reprint requests to: Mr. Takehiko Tsuruta, 1–1–1 Chikushigaoka, Fukuoka 815–8510, Japan. Tel: 81–92–541–1512, Fax: 81–92–552–2707 E-mail: ttsuruta@tohwa-u.ac.jp

Gadd, 1999), and algae(Hosea et al., 1986; Kuyucak and Volesky, 1989). However, there is little information on which kind of microorganisms has a high gold adsorbing ability. In this paper, various species and strains of bacteria, actinomycetes, fungi, and yeasts were screened for their ability to adsorb gold from a solution containing hydrogen tetrachloroaurate (III) or sodium dicyanoaurate (I). Hydrogen tetrachloroaurate(III) is used for medical and ceramic materials. On the other hand, dicyanoaurate (I) is used for plating. Both compounds are popular gold compounds and have a different oxidation stage. The effect of pH, external gold concentration, cell amounts on gold biosorption, and the time course of gold biosorption by Pseudomonas maltophilia cells, which adsorbed large amounts of gold

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from a solution containing hydrogen tetrachloroaurate (III), were investigated in detail. Additionally, in order to develop a practical approach, the determination of a suitable desorbent for gold adsorbed by immobilized P. maltophilia cells and biosorption-desorption cycles was also investigated.
Materials and Methods

Materials. The strains used in this research were generouslydonated by the IAM Culture Collection, Center for Cellular and Molecular Research, Institute of Molecular and Cellular Biosciences, the University of Tokyo (IAM); the Faculty of Engineering, Hiroshima University (HUT); the Faculty of Agriculture, Hokkaido University (AHU); the Institute of Fermentation, Osaka (IFO); and the Central Research Laboratories, Kaken Pharmaceutical, Tokyo (KCC). All of...