Bull. Environ. Contam. Toxicol. (1996) 56:259-264 © 1996 Springer-Verlag New York Inc. Volatilization of Mercury by Resting Mercury-Resistant Bacterial Cells S. Gho sh, P. C. Sadhukhan, D. K. Gho sh, J. Chaudhuri, A. Mandal Department of Biochemistry, University College of Science, 35 Ballygunge Circular Road, Calcutta 700 019, India Received: 18 May 1995/Accepted: 22 August 1995 The mercuric ion reduction system encoded by the Hg 2+ indu- cible mer operon confers bacterial resistance to mercuric ion. The mer A gene product which is a FAD-containing enzyme catalyzes the reduction of Hg 2+ to volatile elemental mercury with the help of intracellular thiols and NADPH as a cofactor (Schottel 1974; Summers and Silver 1978; Fox and Walsh 1982; Misra 1992). Our earlier studies have shown that growing cells of different mercury-resistant bacteria reduce Hg 2+ compounds to Hg(O) (Ray et al. 1989; Pahan et al. 1990a; Gachhui et al. 1989). We have also shown the effect of thiol compounds and flavins on mercury-degrading enzyme activities in mercury-resistant bacteria (Pahan et al. 1990b). Here we report that resting cells of mercury-resistant bacteria survive in a buffer system for several hours, synthesize inducible mercury-degrading enzymes and volatilize mercury from a mercury-containing buffer system. We know of no information regarding studies of mercury-degrad- ing enzymes in resting mercury-resistant bacterial cells. MATERIALS AND METHODS All chemicals and reagents used in this study were of analyti- cal grade. NADPH was purchased from Sigma Chemicals, St. Louis, MO, USA. A broad-spectrum mercury-resistant A zotobacter sp. SS 2 was isolated from soil at the agricultural farm, Giridi, India, and was identified in our laboratory following Bergey's Manual of Determinative Bacteriology, Ninth Edition. This strain was grown aerobically in nutrient broth. A zotobacter sp SS 2 was inoculated in 40 ml of nutrient broth and incubated at 32°C overnight with shaking under air. Over- night culture of bacterial cells was diluted 1:10 with sterile nutrient broth to a final volume of 100 ml. The organisms were Correspondence to: A. Mandal 259