Sulfobacillus benefaciens sp. nov., an acidophilic facultative anaerobic Firmicute isolated from mineral bioleaching operations
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Gram-positive bacteria found as the sole Firmicutes present in two mineral bioleaching stirred tanks, and a third bacterium isolated from a heap leaching operation, were shown to be closely related to each other but distinct from characterized acidophilic iron- and sulfur-oxidizing bacteria of the genus Sulfobacillus, to which they were affiliated. One of the isolates (BRGM2) was shown to be a thermo-tolerant (temperature optimum 38.5°C, and maximum 47°C) obligate acidophile (pH optimum 1.5, and minimum 0.8), and also noted to be a facultative anaerobe, growing via ferric iron respiration in the absence of oxygen. Although isolates BRGM2 and TVK8 were able to metabolize many monomeric organic substrates, their propensity for autotrophic growth was found to be greater than that of Sulfobacillus thermosulfidooxidans and the related acidophile, Sb. acidophilus. Faster growth rates of the novel isolates in the absence of organic carbon was considered to be a major reason why they, rather than Sb. thermosulfidooxidans (which shared many physiological characteristics) more successfully exploited conditions in the stirred tanks. Based on their phylogenetic and phenotypic characteristics, the isolates are designated strains of the proposed novel species, Sulfobacillus benefaciens, with isolate BRGM2 nominated as the type strain.
KeywordsAcidophiles Bioleaching Biomining Firmicute Iron Pyrite Sulfobacillus Sulfur
This work was carried out in the frame of Bioshale (European project contract NMP2-CT-2004 505710) and in the frame of BioMinE (European project contract NMP1-CT-500329-1). The authors acknowledge the financial support given to these projects by the European Commission under the Sixth Framework Programme for Research and Development. We also wish to thank our various partners on the projects for their contributions to the work reported in this paper. The authors would like to thank Hafida El Achbouni for her technical support, Dr D.H. Morin (of BRGM) for providing the BRGM-KCC mixed culture, and Professor Jean Euzéby for his expert advice on bacterial nomenclature. DBJ is grateful to the Royal Society (UK) for the award of an Industrial Fellowship.
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