Abstract
Acidiphilium multivorum LMS is an acidophile isolated from industrial bioreactors during the processing of the gold-bearing pyrite-arsenopyrite concentrate at 38–42 °C. Most strains of this species are obligate organoheterotrophs that do not use ferrous iron or reduced sulfur compounds as energy sources. However, the LMS strain was identified as one of the predominant sulfur oxidizers in acidophilic microbial consortia. In addition to efficient growth under strictly heterotrophic conditions, the LMS strain proved to be an active sulfur oxidizer both in the presence or absence of organic compounds. Interestingly, Ac. multivorum LMS was able to succeed more common sulfur oxidizers in microbial populations, which indicated a previously underestimated role of this bacterium in industrial bioleaching operations. In this study, the first draft genome of the sulfur-oxidizing Ac. multivorum was sequenced and annotated. Based on the functional genome characterization, sulfur metabolism pathways were reconstructed. The LMS strain possessed a complicated multi-enzyme system to oxidize elemental sulfur, thiosulfate, sulfide, and sulfite to sulfate as the final product. Altogether, the phenotypic description and genome analysis unraveled a crucial role of Ac. multivorum in some biomining processes and revealed unique strain-specific characteristics, including the ars genes conferring arsenic resistance, which are similar to those of phylogenetically distinct microorganisms.
Highlights
Gram-negative bacteria of the genus Acidiphilium are members of acidophilic microbial communities in ore deposits, commercial bioleaching operation sites, and acid mine drainage (AMD) [1,2,3,4]
Since arsenic concentrations reach high values during the processing of the gold-containing arsenopyrite concentrates and may be toxic to microorganisms involved in industrial operations, our research focused on the arsenic resistance and unique arsenic resistance genes identified in the genome of the LMS strain
The LMS strain that was assigned to the heterotrophic species Ac. multivorum proved to be among predominant sulfur oxidizers in the commercial acidophilic microbial communities in bioreactors
Summary
Gram-negative bacteria of the genus Acidiphilium are members of acidophilic microbial communities in ore deposits, commercial bioleaching operation sites, and acid mine drainage (AMD) [1,2,3,4]. The roles of phylogenetically close species Ac. cryptum and. Ac. multivorum in acidophilic communities are considered similar to those of other acidophilic organoheterotrophs. The latter can utilize metabolites secreted by acidophilic auto-, hetero-, and mixotrophic microorganisms, as well as organic components of lysed cells, as carbon and energy sources [4]. One of the Acidiphilium species, Ac. acidophilum, has been shown to grow autotrophically with reduced inorganic sulfur compounds (RISCs) [5]. Acidiphilium cryptum strain DX1-1 isolated from AMD of the DeXing mine (Jiangxi Province, China) is able to grow with organic compounds and inorganic sulfur. When sulfur was the sole energy substrate, the growth and sulfur oxidation by the strain DX11 were negligible and improved when glucose was added to the culture medium [6]
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