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

Abstract

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...

Relationship between bioleaching performance, bacterial community structure and mineralogy in the bioleaching of a copper concentrate in stirred-tank reactors

“…thermosulfidooxidans were among the most common species found in stirred tank processes in mesophilic conditions (Olson et al 2003;Dopson and Lindström 2004;Shippers 2007). The reduced number of detected strains demonstrated once more the limited diversity of consortia that thrive in bioleaching processes (Okibe et al 2003). At.…”

“…caldus (Okibe et al 2003;Rawlings 2005). Selection pressure being more important in continuous mode, Sulfobacillus was certainly disadvantaged by the limited availability of CO 2 .…”

The microbiology of biomining: development and optimization of mineral-oxidizing microbial consortia

“…However, conditions (such as concentrations of soluble metals and metalloids) will vary in a continuousflow series of tanks as mineral oxidation becomes increasingly extensive, and this can have a significant impact on diversity and numbers of indigenous microbial species (e.g. Okibe et al, 2003). The homogeneity within an individual tank results in a limited ecological niche that tends often to be dominated by two to four species, although smaller numbers of other micro-organisms may be present (Table 1).…”

Enhancement of Biofilm Formation on Pyrite by Sulfobacillus thermosulfidooxidans

“…Instead of a sole species, microbial populations exhibited substantial diversity in stirred-tank, mineral-processing bioreactors and ore leaching heaps. Microbial community analysis of the leachate has shown that the microbial bioleaching communities varied in commercial mineral leaching operations, but the genus of Sulfobacillus can be detected frequently [6][7][8]. The genus Sulfobacillus was first reported by Golovacheva and Karavaiko in 1978 [9].…”