Characteristics of attachment and growth of <i>Thiobacillus caldus</i> on sulphide minerals: a chemotactic response to sulphur minerals?

281

129

Microorganisms were enumerated and isolated on selective solid media from a pilot-scale stirred-tank bioleaching operation in which a polymetallic sulfide concentrate was subjected to biologically accelerated oxidation at 45°C. Four distinct prokaryotes were isolated: three bacteria (an Acidithiobacillus caldus-like organism, a thermophilic Leptospirillum sp., and a Sulfobacillus sp.) and one archaeon (a Ferroplasma-like isolate). The relative numbers of these prokaryotes changed in the three reactors sampled, and the Ferroplasma isolate became increasingly dominant as mineral oxidation progressed, eventually accounting for >99% of plate isolates in the third of three in-line reactors. The identities of the isolates were confirmed by analyses of their 16S rRNA genes, and some key physiological traits (e.g., oxidation of iron and/or sulfur and autotrophy or heterotrophy) were examined. More detailed studies were carried out with the Leptospirillum and Ferroplasma isolates. The data presented here represent the first quantitative study of the microorganisms in a metal leaching situation and confirm that mixed cultures of iron-and sulfur-oxidizing prokaryotic acidophiles catalyze the accelerated dissolution of sulfidic minerals in industrial tank bioleaching operations. The results show that indigenous acidophilic microbial populations change as mineral dissolution becomes more extensive.The use of microorganisms to recover metals from lowgrade ores and mineral concentrates has developed into a successful and expanding area of biotechnology (32). The microbes catalyze metal recovery either by dissolution of metalcontaining sulfide minerals, such as chalcocite (bioleaching), or by dissolving sulfidic minerals that are intimately associated with the native metal (biooxidation), such as gold in refractory ores, thereby allowing the metal to be extracted by conventional (chemical) means. Different engineering approaches have been used to facilitate microbial mineral processing; these approaches include in situ leaching, dump and heap leaching of low-grade ores, and aerated stirred tanks for microbial processing of mineral concentrates (3). Stirred tanks have several advantages, including the potential to control the bioleaching environment (e.g., pH and temperature) and much shorter turnover times (the times required for mineral processing to be effectively completed), although such systems have large capital and operating costs. Mineral processing operations that use bioreactors generally involve parallel and in-line (primary and secondary) oxidation tanks in order to maximize mineral dissolution.Bioreactor mineral processing initially focused on the treatment of refractory gold sulfide ores. Successful commercial technologies include the BIOX process (5), which operates at ϳ40°C by using mesophilic acidophiles and the Mintek/ Bactech Bacox process, in which utilizes either mesophilic or moderately thermophilic cultures (26). However, the potential to recover other metals, such as Cu, Ni, Zn, and Co, was recognized la...

Section: Discussionmentioning

confidence: 68%

Enumeration and Characterization of Acidophilic Microorganisms Isolated from a Pilot Plant Stirred-Tank Bioleaching Operation

Okibe

Gericke

Hallberg

et al. 2003

281

129

“…digestions, followed by physical disruption by successive freeze-thaw cycles and phenol-chloroform-isoamyl extraction (20). Extracted DNA was precipitated using isopropyl alcohol and 3 M sodium acetate with final resuspension in 50 l of nuclease-free water or Tris-EDTA buffer (TE).…”

mentioning

confidence: 99%

Abundance and Diversity of Archaeal Ammonia Oxidizers in a Coastal Groundwater System

Rogers

Casciotti

2010

Nitrification, the microbially catalyzed oxidation of ammonia to nitrate, is a key process in the nitrogen cycle. Archaea have been implicated in the first part of the nitrification pathway (oxidation of ammonia to nitrite), but the ecology and physiology of these organisms remain largely unknown. This work describes two different populations of sediment-associated ammonia-oxidizing archaea (AOA) in a coastal groundwater system in Cape Cod, MA. Sequence analysis of the ammonia monooxygenase subunit A gene (amoA) shows that one population of putative AOA inhabits the upper meter of the sediment, where they may experience frequent ventilation, with tidally driven overtopping and infiltration of bay water supplying dissolved oxygen, ammonium, and perhaps organic carbon. A genetically distinct population occurs deeper in the sediment, in a mixing zone between a nitrate-and oxygen-rich freshwater zone and a reduced, ammonium-bearing saltwater wedge. Both of these AOA populations are coincident with increases in the abundance of group I crenarchaeota 16S rRNA gene copies.

“…Acidithiobacillus caldus is one of the most abundant microorganisms in industrial biomining (26,31), where it is suggested to oxidize RISCs formed during sulfide mineral breakdown (12,13). Elemental sulfur and tetrathionate are key intermediates in A. caldus metabolism, and tetrathionate hydrolysis yields thiosulfate, pentathionate, and eventually sulfate (6), while S 0 is oxidized to sulfate via sulfite (17).…”

mentioning

confidence: 99%

Regulation of a Novel Acidithiobacillus caldus Gene Cluster Involved in Metabolism of Reduced Inorganic Sulfur Compounds

Rzhepishevska

Valdés

Marcinkevičienė

et al. 2007

Acidithiobacillus caldus has been proposed to play a role in the oxidation of reduced inorganic sulfur compounds (RISCs) produced in industrial biomining of sulfidic minerals. Here, we describe the regulation of a new cluster containing the gene encoding tetrathionate hydrolase (tetH), a key enzyme in the RISC metabolism of this bacterium. The cluster contains five cotranscribed genes, ISac1, rsrR, rsrS, tetH, and doxD, coding for a transposase, a two-component response regulator (RsrR and RsrS), tetrathionate hydrolase, and DoxD, respectively. As shown by quantitative PCR, rsrR, tetH, and doxD are upregulated to different degrees in the presence of tetrathionate. Western blot analysis also indicates upregulation of TetH in the presence of tetrathionate, thiosulfate, and pyrite. The tetH cluster is predicted to have two promoters, both of which are functional in Escherichia coli and one of which was mapped by primer extension. A pyrrolo-quinoline quinone binding domain in TetH was predicted by bioinformatic analysis, and the presence of an o-quinone moiety was experimentally verified, suggesting a mechanism for tetrathionate oxidation.