Reduction of Selenate and Selenite to Elemental Selenium by a Pseudomonas stutzeri Isolate.

A Pseudomonas stutzeri isolate rapidly reduced both selenite and selenate ions to elemental selenium at initial concentrations of both anions of up to 48.1 mM. Optimal selenium reduction occurred under aerobic conditions between pH 7.0 and 9.0 and at temperatures of 25 to 35 degrees C. Reduction of both selenite and selenate was unaffected by a number of anions except for sulfite, chromate, and tungstate ions, which inhibited both growth and reduction.

The continuous recovery of uranium from biologically leached solutions using immobilized biomass.

The potential of uranium recovery from the dilute uranium ore bioleach solutions of the Elliot Lake district of Canada was examined using immobilized microbial biomass. Batch and continuous laboratory scale pilot plant experiments were carried out. The results have shown that the immobilized microbial biomass can successfully recover all of the uranium from dilute (less than 300 mg U/L) solutions. The uranium can subsequently be eluted producing a high uranium concentration eluate perhaps exceeding 5000 mg U/L. The biomass maintained its biosorption capacity of about 50 mg U/g over 12 examined successive adsorption-elution cycles with no apparent indication of failure.

Sulfur isotope fractionation by Proteus vulgaris and Salmonella heidelberg during the reduction of thiosulfate.

Proteus vulgaris metabolized thiosulfate to H2S. The amount evolved and its sulfur isotope composition identified it solely with sulfane sulfur. In contrast, Salmonella heidelberg sequentially reduced the sulfane sulfur of S2O3(-2) with slight enrichment of the evolved sulfide in 32S and then reduced the sulfonate sulfur of S2O3(-2) with large isotopic selectivities and an inverse isotopic fractionation pattern. The inverse isotope fractionation pattern for the H2S derived from the sulfonate sulfur was almost identical to that observed during the reduction of high concentrations of sulfite by S. heidelberg.

Sulfur isotope fractionation by Salmonella heidelberg: inverse isotope effects during growth on high concentrations of Na2SO3.

During growth on minimal salts - glucose media supplemented with high concentrations of Na2SO3 (10-3 and 10-2 M), Salmonella heidelberg exhibited cytological and growth responses which indicated increased cellular toxicity with increasing sulfite concentrations. The large quantities of sulfide evolved during growth at both SO32- concentrations were accompanied by large normal and inverse isotope effects. Consistent with earlier findings, this organism was found capable of rapidly metabolizing both the sulfane and sulfonate sulfur of thiosulfate. Therefore, the isotope effects do not appear to be caused by extracellular chemical thiosulfate formation.

The effect of pantothenate on sulfate metabolism and sulfur isotope fractionation by Saccharomyces cerevisiae.

Growth of Saccharomyces cerevisiae in minimal salts-glucose-SO4(2-) medium with varying concentrations of pantothenate (0-1000 microgram/L) produced changes in the cellular lipid content and in the ratio of saturated to unsaturated fatty acids. Substantial differences in SO4(2-) diffusion were also observed with changes in pantothenate concentration. During sulfate reduction, the delta 34S value of the evolved sulfide varied with the pantothenate concentration ranging from -31% in the absence of pantothenate to 0% at 400-1000 microgram/L pantothenate. The isotope selectivity is related to the effect of pantothenate concentration on cellular metabolism.

The use of stable sulfur isotope labelling to elucidate sulfur metabolism by Clostridium pasteurianum.

An unique isotope labelling experiment was conducted whereby mixtures of sulfate and sulfite of different isotopic compositions were metabolized by Clostridium pasteurianum. The results showed during reduction of 1 mM SO3= plus 1 mM SO4=, essentially all evolved H2S arose from the sulfite whereas in the case of cellular sulfur, 85% was derived from sulfite and the remainder from sulfate.

Morphological modifications of cells of Clostridium pasteurianum caused by growth on sulfite.

The morphology of Clostridium pasteurianum cells grown on 10(-2) M SO32- showed significant alteration in cell shape and the absence of the electron translucent reserve polysaccharide (amylopectin) when compared to sulfate-grown cells. At the lower sulfite concentrations (10(-3) and 10(-4)M SO32-) the cells showed the cytoplasmic changes noted above but the cell shapes were not modified.

Stable isotope fractionation by Clostridium pasteurianum. 1. 34S/32S: inverse isotope effects during SO4-2- and SO3-2- reduction.

During growth on minimal salts--sucrose media supplemented with various concentrations (10-4-10-2 M) of sodium sulfate, Clostridium pasteurianum grew at a normal rate and only evolved sulfide in late stages of growth on 10-2 M SO4-2-. The evolved sulfide was slightly enriched in 34S as compared to the medium sulfur. On the other hand, sulfide was evolved during growth on all concentrations of sulfite tested. Large normal and inverse isotopic effects were observed in the evolved sulfide during SO3-2- reductions. In contrast, the intracellular sulfur showed much smaller fractionations. The complexity of the isotopic patterns suggests that a dissimilatory sulfite reductase system may be induced by high concentrations of sulfite.