Browsing by Author "Okibe, Naoko"
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- Ferrimicrobium acidiphilum gen. nov., sp. nov. and Ferrithrix thermotolerans gen. nov., sp. nov.: heterotrophic, iron-oxidizing, extremely acidophilic actinobacteriaPublication . Johnson, D. Barrie; Nicolau, Paula Bacelar; Okibe, Naoko; Thomas, Angharad; Hallberg, Kevin B.Two novel extremely acidophilic, iron-oxidizing actinobacteria were isolated, one from a mine site in North Wales, UK (isolate T23T), and the other from a geothermal site in Yellowstone National Park, Wyoming, USA (Y005T). These new actinobacteria belong to the subclass Acidimicrobidae, and in contrast to the only other classified member of the subclass (Acidimicrobium ferrooxidans), both isolates were obligate heterotrophs. The mine site isolate was mesophilic and grew as small rods, while the Yellowstone isolate was a moderate thermophile and grew as long filaments, forming macroscopic flocs in liquid media. Both isolates accelerated the oxidative dissolution of pyrite in yeast extract-amended cultures, but neither was able to oxidize reduced forms of sulfur. Ferrous iron oxidation enhanced growth yields of the novel mesophilic actinobacterium T23T, though this was not confirmed for the Yellowstone isolate. Both isolates catalysed the dissimilatory reduction of ferric iron, using glycerol as electron donor, in oxygen-free medium. Based on comparative analyses of base compositions of their chromosomal DNA and of their 16S rRNA gene sequences, the isolates are both distinct from each other and from Acidimicrobium ferrooxidans, and are representatives of two novel genera. The names Ferrimicrobium acidiphilum gen. nov., sp. nov. and Ferrithrix thermotolerans gen. nov., sp. nov. are proposed for the mesophilic and moderately thermophilic isolates, respectively, with the respective type strains T23T (5DSM 19497T5ATCC BAA-1647T) and Y005T (5DSM 19514T5ATCC BAA-1645T).
- Role of pure and mixed cultures of gram-positive eubacteria in mineral leachingPublication . Johnson, D. Barrie; Nicolau, Paula Bacelar; Okibe, Naoko; Yahya, Adibah; Hallberg, Kevin B.Research on the biooxidation of sulfidic minerals has tended to be heavily biased towards Gram-negative bacteria, such as Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans. Currently, just three species of mineral-oxidising Gram-positive bacteria are recognised: Sulfobacillus thermosulfidooxidans, Sulfobacillus acidophilus and Acidimicrobium (Am.) ferrooxidans, all of which are thermotolerant prokaryotes. We have isolated and characterised a number of phylogenetically distinct Gram-positive ironmetabolising bacteria, including mesophilic and moderately thermophilic strains. Mesophilic isolates include (i) novel Sulfobacillus spp., some of which are the more acidophilic than all known iron-oxidising bacteria, (ii) "Ferrimicrobium acidiphilum", an actinobacterium most closely related to Am. ferrooxidans, and (iii) a group of low GC Gram-positives which appear to represent a novel genus. Moderately thermophilic isolates include a novel Sulfobacillus sp., an Alicyclobacillus spp. that, in contrast to currently recognised species, grows anaerobically by reduction of ferric iron and thrives in mineral leaching environments, and a new genus/species of iron- and sulfur-oxidising bacterium with the proposed name "Caldibacillus ferrivorus". These novel prokaryotes exhibited varying degrees of mineral leaching efficiencies, with the mesophilic Sulfobacillus spp. being particularly adept at solubilising pyrite at very low (<1) pH values. All novel Gram-positive isolates catalysed the oxidative dissolution of pyrite at lower redox potentials than Gram-negative mesophiles. Mixed cultures of Gram-positive bacteria, either with other Gram-positives or with Gram-negative bacteria, were often more effective mineral-leaching systems than corresponding pure cultures.