Some properties of a novel obligately autotrophic iron-oxidizing bacterium isolated from seawater

An iron-oxidizing bacterium obligately requiring NaCl for growth was isolated from seawater in Seto Inland Sea, Japan, and designated as strain KU2-11. Strain KU2-11 was a Gram negative, non-spore-forming and rod-shaped bacterium, and can grow autotrophically by using ferrous ion and elemental sulfur as sole energy sources. The optimum growth pH and temperature were 2 and 30°C, respectively. The G+C content of the DNA was 59 mol%. The bacterium could not grow in the medium without NaCl and obligately required NaCl for growth. The optimum NaCl concentration for the growth was 2%. Strain KU2-11 seemed to be identified as a member of Thiobacillus ferrooxidans on the basis of morphological and physiological properties. However, the phylogenetic analysis based on 16S rDNA gene sequences indicated that strain KU2-11 is distinct from T. ferrooxidans. Iron- and sulfur-oxidizing activity of the bacterium were not detected in a reaction mixture without NaCl, and depended on the presence of NaCl. The optimum NaCl concentrations for the iron- and sulfur-oxidizing activities were 2-4% and 1%, respectively. On the basis of the phenotypic characteristics of strain KU2-11 and its phylogenetic position, we suggested that this bacterium should be placed in a new species of the genus Thiobacillus.