INTERACTION OF SULFATE-REDUCING BACTERIA WITH MOLYBDENUM DISSOLVED FROM SPUTTER-DEPOSITED MOLYBDENUM THIN-FILMS AND PURE MOLYBDENUM POWDER

When sputter-deposited Mo thin films were exposed to sulfate-reducing bacterium Desulfovibrio desulfuricans, dissolved Mo markedly delayed t he culture growth and reduced the rate of sulfate reduction. The inter action led to an orange coloration of the culture liquid. X-ray photoe lectron spectroscopy of dried culture droplets revealed that Mo dissol ution products existed mostly in pentavalent state, and a smaller amou nt of molybdate and molybdenum disulfide, In contrast, Mo dissolution in uninoculated medium was negligible. Subsequently, different concent rations of molybdate, ranging from 0.1 to 20 mM, were added to the gro wth medium and it was found that a low concentration of molybdate (1 m M) was able to reduce the culture growth rate and sulfate reduction by forming Mo(V)-S complexes. In order to study the dependence of the de gree of interaction upon microbial activity and growth-dependent metab olic products, 1.0 g/L Mo powder was added to (a) the growth medium, ( b) a 3-day-old culture, and, (c) the supernatants of 2 h to 5-day-old cultures. Ultraviolet-visible spectroscopy indicated that the Mo(V)-S complexes consisted of a Mo-S compound analogous to a binuclear dioxob ridged Mo(V)-cysteine complex (314 nm) and Mo(V)-containing molybdenyl thiocyanate (468 nm). Dissolution of Mo was induced by H2S, a product of the bacterial sulfate reduction, and was further increased probabl y by sulfur-containing amino groups and proteins. (C) 1998 Academic Pr ess.