Browsing by Author "Campbell, Scott C."

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Biogenic production of cyanide and its application to gold recovery
(2001-03) Campbell, Scott C.; Clark, T. R.; McFeters, Gordon A.
Chromobacterium violaceum is a cyanogenic (cyanide-producing) microorganism. Cyanide is used on an industrial scale to complex and recover gold from ores or concentrates of ores bearing the precious metal. A potentially useful approach in gold mining operations could be to produce cyanide biologically in relatively small quantities at the ore surface. In this study, C. violaceum grown in nutrient broth formed a biofilm and could complex and solubilize 100% of the fold on glass test slides within 4-7 days. Approximately 50% of cyanide-recoverable gold could be mobilized from a biooxidized sulfidic-ore concentrate. Complexation of cyanide in solution by gold appeared to have a beneficial effect of cell growth- viable cell counts were nearly two orders of magnitude greater in the presence of gold-coated slides or biooxidized ore substrates that in their absence. C. violaceum was cyanogenic when grown in alternative feedstocks. When grown in a mineral salt solution supplemented with 13.3% v/v swine fecal material (SFM), cells exhibited pigmentation and suspended cell concentrations comparable to cultures grown in nutrient broth. Glycine supplements stimulated production of cyanide in 13.3% v/v SFM. In contrast, glycine was inhibitory when added at the time of inoculation in the more concentrated SFM, decreasing cell numbers and reducing ultimate bulk-solution cyanide concentration. However, aeration and addition of glycine to stationary phase cells grown on 13.3% v/v SFM anaerobically resulted in rapid production and high concentrations (up to 38 mg I-1) of cyanide. This indicates that biogenesis of cyanide may be supported in remote areas using locally produced and inexpensive agricultural feedstocks in place of commercial media.
Influence of the distribution of the manganese-oxidizing bacterium, Leptothrix discophora, on ennoblement of type 316L stainless steel
(2004-07) Campbell, Scott C.; Geesey, Gill G.; Lewandowski, Zbigniew; Jackson, G.
Type 316L (UNS 31603) stainless steel (SS) was ennobled to an open-circuit potential (OCP) of 323 mV vs saturated calomel electrode (SCE) within a 5-day period due to the deposition of manganese oxides on the metal surface by a monospecies biofilm of Leptothrix discophora. However, the same metal experienced only partial ennoblement, achieving a maximum potential of 143 mVSCE during the same period when colonized by a three-species biofilm containing L. discophora, and even this level of ennoblement by the mixed-species biofilm was only transient since the potential decreased to 122 mVSCE shortly after achieving the maximum potential. The mixed-species biofilm was significantly thicker (>200 µm) than the L. discophora monospecies biofilm (120 µm). Using 16s rRNA probes specific for L. discophora, fluorescent in-situ hybridization revealed cells to be heterogeneously distributed throughout the monospecies biofilm. In the three-species biofilm, 16s rRNA probes revealed a homogeneous layer of L. discophora that resided proximal to the biofilm-bulk solution phase. At the most distal position from the biofilm-bulk solution phase near the glass-biofilm interface there existed very few to no L. discophora. Microelectrode studies revealed the presence of oxygen (3.85 mg/L to 4.35 mg/L) at the monospecies-glass substratum interface in 50% of the areas of the substratum assayed. No oxygen was detected at the three-species biofilm-glass interface where the thickness of the overlying biofilm exceeded 200 µm. The results suggest that ennoblement of Type 316L SS by L. discophora depends on oxygen accessibility to cells proximal to the substratum.