Iron Demand by Thermophilic and Mesophilic Bacteria Isolated from an Antarctic Geothermal Soil

The thermophilic bacterial strain MP4 assigned to a new species, likely of the genus Alicyclobacillus, was isolated from geothermal soils on the NW slope of Mount Melbourne, Antarctica. These soils have high iron concentrations and the strain MP4 requires iron additions for growth. Four mesophilic bacterial strains Paenibacillus validus MP5, MP8, and MP10, and P. apiarius MP7, isolated from the same site, need iron supply for growth depending on the medium. Growth temperature of thermophilic strain ranges from 42 to 70 °C, and that one of mesophiles from 25 to 44 °C. Thermophilic and mesophilic strains shared microenvironments with temperature of 42–44 °C and showed optima of pH values ranging from 5.5 to 6.0. The thermophilic strain MP4 reached values of 10⁶ CFU ml⁻¹ in aqueous soil extract from the NW slope of Mt. Melbourne, and 10⁵ CFU ml⁻¹ in water extracts from other geothermal Antarctic areas (Mt. Rittmann and Cryptogam Ridge). Growth of thermophilic bacteria in aqueous extracts of the NW slope of Mount Melbourne soils caused a reduction of 50% of soluble iron content, which was recovered in bacterial biomass. These results suggest a possible involvement of the thermophilic strain MP4 in iron bioavailability in these geothermal soils.