Growth of Thiobacillus ferrooxidans: a Novel Experimental Design for Batch Growth and Bacterial Leaching Studies

The concentrations of ferrous and ferric ions change dramatically during the course of the batch experiments usually performed to study the kinetics of the bacterial oxidation of ferrous ions and sulfide minerals. This change in concentration of the iron species during the course of the experiment often makes it difficult to interpret the results of these experiments, as is evidenced by the lack of consensus concerning the mechanism of bacterial leaching. If the concentrations of ferrous and ferric ions were constant throughout the course of the batch experiment, then the role of the bacteria could be easily established, because the rate of the chemical leaching should be the same at a given redox potential in the presence and in the absence of bacteria. In this paper we report an experiment designed to obtain kinetic data under these conditions. The redox potential is used as a measure of the concentrations of ferrous and ferric ions, and the redox potential of the leaching solution is controlled throughout the experiment by electrolysis. The effects of ferrous, ferric, and arsenite ions on the rate of growth of Thiobacillus ferrooxidans on ferrous ions in this redox-controlled reactor are presented. In addition, the growth of this bacterium on ferrous ions in batch culture was also determined, and it is shown that the parameters obtained from the batch culture and the redox-controlled batch culture are the same. An analysis of the results from the batch culture indicates that the initial number of bacteria that are adapted to the solution depends on the concentrations of ferrous and arsenite ions.     

A new synthesis of furanoid fatty acids: isomerisation of hydroxy-cis-enynoic acids by alkali, and on argentous silica gel

Novel hydroxy-cis-enynoic acids have been prepared. Those of type

C(CH₂)₆CO₂H have been found to cyclise to furanoid acids on treatment with alkali, or on chromatography on argentous silica gel. The hydroxy-cis-enynoic acids stimulate smooth muscle, the furanoid acids are not similarly active.     

Leaching of Zinc Sulfide by Thiobacillus ferrooxidans: Experiments with a Controlled Redox Potential Indicate No Direct Bacterial Mechanism

The role of Thiobacillus ferrooxidans in bacterial leaching of mineral sulfides is controversial. Much of the controversy is due to the fact that the solution conditions, especially the concentrations of ferric and ferrous ions, change during experiments. The role of the bacteria would be more easily discernible if the concentrations of ferric and ferrous ions were maintained at set values throughout the experimental period. In this paper we report results obtained by using the constant redox potential apparatus described previously (P. I. Harvey and F. K. Crundwell, Appl. Environ. Microbiol. 63:2586–2592, 1997). This apparatus is designed to control the redox potential in the leaching compartment of an electrolytic cell by reduction or oxidation of dissolved iron. By controlling the redox potential the apparatus maintains the concentrations of ferrous and ferric ions at their initial values. Experiments were conducted in the presence of T. ferrooxidans and under sterile conditions. Analysis of the conversion of zinc sulfide in the absence of the bacteria and analysis of the conversion of zinc sulfate in the presence of the bacteria produced the same results. This indicates that the only role of the bacteria under the conditions used is regeneration of ferric ions in solution. In this work we found no evidence that there is a direct mechanism for bacterial leaching.     

Isoform-specific O-glycosylation by murine UDP-GalNAc:polypeptide N- acetylgalactosaminyltransferase-T3, in vivo

Multiple isoforms of UDP-GalNAc:polypeptide N-acetylgalactosaminyl- transferase (ppGaNTase) have been cloned and expressed from a variety of organisms. In general, these isoforms display different patterns of tissue-specific expression, but exhibit overlapping substrate specificities, in vitro . A peptide substrate, derived from the sequence of the V3 loop of the HIV gp120 protein (HIV peptide), has previously been shown to be glycosylated in vitro exclusively by the ppGaNTase-T3 (Bennett et al. , 1996). To determine if this isoform- specificity is maintained in vivo , we have examined the glycosylation of this substrate when it is expressed as a reporter peptide (rHIV) in a cell background (COS7 cells) which lacks detectable levels of the ppGaNTase-T3. Glycosylation of rHIV was greatly increased by coexpression of a recombinant ppGaNTase-T3. Overexpression of ppGaNTase- T1 yielded only partial glycosylation of the reporter. We have also determined that the introduction of a proline residue at the +3 position flanking the potential glycosylation site eliminated ppGaNTase- T3 selectivity toward rHIV observed both in vivo and in vitro .      

Intraspecific morphological variation in late Miocene Bolboforma, and implications for their classification, ecology, and biostratigraphic utility

A preliminary morphological study of large, well preserved bolboform populations from the late Miocene section of DSDP Site 593, in the southern Tasman Sea, reveals a relationship between test size and intraspecific morphological variation interpreted as a gradual transformation in test shape and surface ornamentation. The succession begins with small, smooth, thin-walled subspheroidal tests. As test size increases, rudimentary ornaments become more common and the shape more globose. With further size increase, the walls thicken and ornaments become more structured, but specimens still retain a rounded globose shape. In still larger tests, the ornament becomes more prominent and tests develop a squatter shape with flatter aboral surfaces. The transformation generally ends with large, thick-walled, highly ornate forms with squat globose tests, robust ornaments, and relatively flat aboral surfaces. Although the size of the test increases notably through the transformation, there appears to be no corresponding change in the internal chamber size from its initial value, and so the transformation is largely due to the addition of calcite to the outer surface of the test wall. This appears to be an inherent biological feature and does not involve calcite dissolution/reprecipitation or other retrograde processes. The detail of the transformation varies between species and is presented here for Bolboforma subfragoris s.l., B. gruetzmacheri n. sp., and B. metzmacheri s.s., which exhibit different types of ornament — spinose, irregularly ridged, and cancellate, respectively.When different morphological forms of a single species occur in the same sample, they have the potential to be interpreted as different species. Taxonomic confusion is further compounded by the morphological similarity of many small, smooth-walled, and weakly ornamented forms of different species. These features are common in bolboform populations and have contributed to the misinterpretation of some species. Differences in test shape and ornament are most notable in large ornate forms and taxonomic interpretations should be based wherever possible on such forms. Once the taxonomy is clear, the biostratigraphic utility of the late Miocene bolboforms from Site 593 has been in the recognition of single species (or at most two) in a given sample. This provides an excellent biostratigraphic framework for a period of time that lacks significant alternative microfossils for age control in New Zealand sediments.The distribution of bolboforms in (mainly) southern hemisphere marine sediments appears to track the palaeocirculation of Southern Component Intermediate Water (SCIW). Hence addition of calcite to the outer surface of the test wall probably occurred while the bolboforms were entrained in subsurface flows of SCIW. In this respect, the increased complexity of ornamentation may have been a morphological adaptation to counter the loss of buoyancy as calcite was added to the outer surface of the test wall. This would have presumably contributed to the entrainment and dispersal of bolboforms in the flow of subsurface water masses, and it suggests that the tests of some bolboforms at least may represent a dispersal phase in the life cycle of this enigmatic group of microfossils.     

Mechanism of Pyrite Dissolution in the Presence of Thiobacillus ferrooxidans

In spite of the environmental and commercial interests in the bacterial leaching of pyrite, two central questions have not been answered after more than 35 years of research: does Thiobacillus ferrooxidans enhance the rate of leaching above that achieved by ferric sulfate solutions under the same conditions, and if so, how do the bacteria affect such an enhancement? Experimental conditions of previous studies were such that the concentrations of ferric and ferrous ions changed substantially throughout the course of the experiments. This has made it difficult to interpret the data obtained from these previous works. The aim of this work was to answer these two questions by employing an experimental apparatus designed to maintain the concentrations in solution at a constant value. This was achieved by using the constant redox potential apparatus described previously (P. I. Harvey, and F. K. Crundwell, Appl. Environ. Microbiol. 63:2586–2592, 1997; T. A. Fowler, and F. K. Crundwell, Appl. Environ. Microbiol. 64:3570–3575, 1998). Experiments were conducted in both the presence and absence of T. ferrooxidans, maintaining the same conditions in solution. The rate of dissolution of pyrite with bacteria was higher than that without bacteria at the same concentrations of ferrous and ferric ions in solution. Analysis of the dependence of the rate of leaching on the concentration of ferric ions and on the pH, together with results obtained from electrochemical measurements, provided clear evidence that the higher rate of leaching with bacteria is due to the bacteria increasing the pH at the surface of the pyrite.     

Leaching of Zinc Sulfide by Thiobacillus ferrooxidans: Bacterial Oxidation of the Sulfur Product Layer Increases the Rate of Zinc Sulfide Dissolution at High Concentrations of Ferrous Ions

This paper reports the results of leaching experiments conducted with and without Thiobacillus ferrooxidans at the same conditions in solution. The extent of leaching of ZnS with bacteria is significantly higher than that without bacteria at high concentrations of ferrous ions. A porous layer of elemental sulfur is present on the surfaces of the chemically leached particles, while no sulfur is present on the surfaces of the bacterially leached particles. The analysis of the data using the shrinking-core model shows that the chemical leaching of ZnS is limited by the diffusion of ferrous ions through the sulfur product layer at high concentrations of ferrous ions. The analysis of the data shows that diffusion through the product layer does not limit the rate of dissolution when bacteria are present. This suggests that the action of T. ferrooxidans in oxidizing the sulfur formed on the particle surface is to remove the barrier to diffusion by ferrous ions.     

Modeling, simulation, and optimization of bacterial leaching reactors

Bacterial leaching represents an unusual problem in biochemical engineering, because the substrate for bacterial growth is not supplied directly, but is a product of another reaction, the leaching of mineral particles. In addition, leaching is a heterogeneous reaction dependent on the particle-size distribution in the feed and on the kinetics of particle shrinkage. In this study, these effects are incorporated in the material balance for each mineral by the number balance. Examination of the number balance gives rise to a novel analysis of the competing technologies for leaching. The model is completed by the addition of material balances for the ferrous and ferric ions, the dissolved oxygen, and for each bacterial species to the number balance for each mineral present in the feed. The model is compared with pilot plant data for three different ores. It is shown that the model is in excellent agreement with the data. The performance of a bacterial leaching reactor is explored using the model, and the washout and sensitivity criteria are determined. It is shown that there are three washout conditions, in which the leaching conversion drops to zero. The washout conditions are dependent on the growth rate of the bacteria, on the rate of dissolution of the mineral, and on the rate of mass transfer of oxygen to the reactor. The critical washout condition is that arising from the rate of mineral dissolution. The optimization of a plant in which continuous tank reactors are configured in series is addressed. This analysis shows that the primary reactor should be between 1.5 and 2 times the size of each of the secondary reactors in a series combination.     

Leaching of zinc sulfide by Thiobacillus ferrooxidans: bacterial oxidation of the sulfur product layer increases the rate of zinc sulfide dissolution at high concentrations of ferrous ions

This paper reports the results of leaching experiments conducted with and without Thiobacillus ferrooxidans at the same conditions in solution. The extent of leaching of ZnS with bacteria is significantly higher than that without bacteria at high concentrations of ferrous ions. A porous layer of elemental sulfur is present on the surfaces of the chemically leached particles, while no sulfur is present on the surfaces of the bacterially leached particles. The analysis of the data using the shrinking-core model shows that the chemical leaching of ZnS is limited by the diffusion of ferrous ions through the sulfur product layer at high concentrations of ferrous ions. The analysis of the data shows that diffusion through the product layer does not limit the rate of dissolution when bacteria are present. This suggests that the action of T. ferrooxidans in oxidizing the sulfur formed on the particle surface is to remove the barrier to diffusion by ferrous ions.