Effect of ferric sulfate on activity of moderately thermophilic acidophilic iron-oxidizing microorganisms

The effect of high ferric sulfate concentrations on the organisms predominating in biohydrometallurgical processes (bacteria of genus Sulfobaсillus and archaea of the genus Acidiplasma) was studied. Ability of the studied strains to grow and oxidize ferrous iron in the media with 125 to 500 mM ferric sulfate was determined. High concentrations of ferric sulfate significantly inhibited the oxidative activity and growth of the studied microorganisms. Bacteria of the genus Sulfobaсillus were found to be incapable of active iron oxidation in the presence of ferric iron sulfate at concentrations exceeding 250 mM. Archaea of the genus Acidiplasma oxidized ferrous iron completely in the presence of 500 mM Fe³⁺. Microbial growth was suppressed by relatively low ferric sulfate concentrations. Almost no growth occurred at ferric sulfate concentrations exceeding 199 mM, while lysis of the cells of all studied strains was observed at higher Fe³⁺ concentrations. Archaea (genus Acidiplasma, family Ferroplasmaceae) were shown to be more tolerant to high ferric sulfate concentrations than bacteria of the genus Sulfobaсillus. The results obtained may be used for improvement of biohydrometallurgical technologies and are also important for the understanding of the patterns of formation of microbial communities carrying out the technological processes.     

Morphological and ultrastructural study of the cell envelope of thermophilic and acidophilic microorganisms as compared to Thiobacillus ferrooxidans

The cell envelope of a Sulfolobus-like microorganism has an arrayed hexagonal subunit structure, a double-layered cytoplasmic membrane, and a hollow periplasmic space between the plasma membrane and the outermost arrayed layer. A dense peptidoglycan layer outside the plasma membrane found in the case of Thiobacillus ferrooxidans was not seen. The cell envelope of a thermophile isolated from a leaching environment has a well-defined envelope with two well-stained layers distinclty seen. While the peptidoglycan layer is also not seen in this thermophile, a long flagellum similar to that in the case of T. ferrooxidans is present. The presence of pili in the Sulfolobus-like organism and its arrayed subunit cell envelope structure could account for the organism's selective attachment to sulfide phases in the leaching of low-grade ores. The observations of a well-defined cell envelope in the two thermophiles is consistent with the structure-function relationship previously established for T. ferrooxidans.     

Bioregeneration of the pregnant leach solutions obtained during the leaching of nonferrous metals from slag waste by acidophilic microorganisms

The bioregeneration of the solutions obtained after the leaching of copper and zinc from slag waste by sulfuric acid solutions containing ferric iron was examined. For bioregeneration, associations of mesophilic and moderately thermqophilic acidophilic chemolithotrophic microorganisms were made. It has been shown that the complete oxidation of iron ions in solutions is possible at a dilution of the pregnant leach solution with a nutrient medium. It has been found that the maximal rate of oxidation of iron ions is observed at the use of a mesophilic association of microorganisms at a threefold dilution of the pregnant leach solution with a nutrient medium. The application of bioregeneration during the production of nonferrous metals from both copper converter slag and its waste would make it possible to approach the technology of their processing using the closed cycle of workflows.     

Emulsifying activity in thermophilic and extremely thermophilic microorganisms

Thermophilic and extremely thermophilic enrichments from several different environments produced cell-associated emulsifiers as did several pure cultures ofArchaea. The bioemulsifiers were effective over a wide range of pH, at NaCl concentrations up to 200 g L^–1, and at temperatures up to 80°C. The emulsifying activity in cell-free extracts ofMethanobacterium thermoautotrophicum was a cell-associated protein with a molecular weight greater than 5000 Da. This emulsifier formed viscous emulsions, but did not reduce the surface tension of water or the interfacial tension between water and hexadecane. The emulsifier had the greatest activity with alkanes with carbon numbers greater than 10. The characteristics of the bioemulsifier fromM. thermoautotrophicum makes it suitable for use in saline or thermophilic oil reservoirs as a mobility control agent or in well-bore clean up processes.     

Characteristics of a moderately thermophilic and acidophilic iron-oxidizing Thiobacillus

Summary Thiobacillus TH1 is an acidophilic chemolithotrophic heterotroph growing at temperatures up to about 50°C on media containing ferrous iron or pyrite when supplemented with yeast extract or glutathione. Virtually no carbon dioxide fixation occurred during growth on iron with yeast extract. Its DNA contains 48 mol % guanine + cytosine. The organism effects the thermophilic leaching of metals from pyrite, chalcopyrite, CuS, and copper concentrates. Oxidation of soluble ferrous iron at pH 1.6 was competitively inhibited by ferric iron and had a K_m of 7.3 mM FeSO₄.     

Ultrastructure of an extremely thermophilic acidophilic micro-organism.

A thermoacidophilic micro-organism, isolated from volcanic hot springs near Naples, was cultivated in vitro, and examined by electron microscopy in sections and after negative staining. The cells were almost spherical, with a diameter of about 0.7 to 1.0 mum. Their morphology was very primitive: the protoplasm was composed only of ground cytoplasm, ribosomes, and randomly distributed DNA strands. They were surrounded by a plasma membrane and by an extracellular coat about 20 nm thick which displayed a regular hexagonal pattern. Cell replication occurred by binary fission with median constriction during which a bipolar localization of nuclear material was observable. The morphology is compared with that of other known micro-organisms living in similar habitats.     

Extremely thermophilic acidophilic bacteria convergent with Sulfolobus acidocaldarius.

A series of extremely thermophilic acidophilic bacteria has been characterized as closely resembling the species Sulfolobus acidocaldarius except for a totally different guanosine-cytosine content in the DNA; some conceptual consequences of this situation are discussed. Both organisms also share special features, including a very characteristic type of ether lipid, with other extreme acidophilic thermophiles.     

The degradation of lignocellulosics by extremely thermophilic microorganisms

Five extremely thermophilic cellulose-degrading isolates obtained from New Zealand thermal springs were tested for their ability to degrade a number of natural lignocellulosic substrates. Degradation by three of the isolates was generally similar to that by the moderate thermophile, Clostridium thermocellum but occurred at a higher temperature. The New Zealand isolates were also found to grow on xylan as sole carbohydrate source, which probably extends their attack to hemicellulose.     

Oxidation of sulfur-containing substrates by an association of acidophilic chemolithotrophic microorganisms

Quantitative and qualitative changes in the content of elements in the solid and liquid phases occurred as the pulp moved through reactors during biooxidation of an ore flotation concentrate. The association of microorganisms were adapted for utilizing sulfur-containing substrates; however, the rate of their oxidation was insufficient, which led to an increase in the amount of sodium cyanide required for gold recovery. The replacement of one-fourth of the liquid phase of the pulp (density, 13%) with a mineral medium without an energy source, the fractional addition of FeSO₄ · 7H₂O (1 g/l per day), and the improvement of pulp aeration made it possible to increase the content of SO ₄ ^2? by 80.7, 86.2, and 58.5%, respectively. When one-fourth of the liquid phase of the pulp (density, 24%) was replaced with a mineral medium without an energy source, the rate of additional oxidation of sulfide minerals increased, which increased the efficiency of gold extraction into solution and gold recovery on charcoal by 3.4 and 3.6%, respectively, and reduced sodium cyanide consumption by 3 kg/ton.     

Biodiversity, metabolism and applications of acidophilic sulfur-metabolizing microorganisms

Extremely acidic, sulfur-rich environments can be natural, such as solfatara fields in geothermal and volcanic areas, or anthropogenic, such as acid mine drainage waters. Many species of acidophilic bacteria and archaea are known to be involved in redox transformations of sulfur, using elemental sulfur and inorganic sulfur compounds as electron donors or acceptors in reactions involving between one and eight electrons. This minireview describes the nature and origins of acidic, sulfur-rich environments, the biodiversity of sulfur-metabolizing acidophiles, and how sulfur is metabolized and assimilated by acidophiles under aerobic and anaerobic conditions. Finally, existing and developing technologies that harness the abilities of sulfur-oxidizing and sulfate-reducing acidophiles to extract and capture metals, and to remediate sulfur-polluted waste waters are outlined.     

Metal resistance in acidophilic microorganisms and its significance for biotechnologies

Extremely acidophilic microorganisms have an optimal pH of <3 and are found in all three domains of life. As metals are more soluble at acid pH, acidophiles are often challenged by very high metal concentrations. Acidophiles are metal-tolerant by both intrinsic, passive mechanisms as well as active systems. Passive mechanisms include an internal positive membrane potential that creates a chemiosmotic gradient against which metal cations must move, as well as the formation of metal sulfate complexes reducing the concentration of the free metal ion. Active systems include efflux proteins that pump metals out of the cytoplasm and conversion of the metal to a less toxic form. Acidophiles are exploited in a number of biotechnologies including biomining for sulfide mineral dissolution, biosulfidogenesis to produce sulfide that can selectively precipitate metals from process streams, treatment of acid mine drainage, and bioremediation of acidic metal-contaminated milieux. This review describes how acidophilic microorganisms tolerate extremely high metal concentrations in biotechnological processes and identifies areas of future work that hold promise for improving the efficiency of these applications.