Biochemical Characterization and Electrochemical Cultivation of Halotolerant Autotrophic Iron-Oxidizing Bacteria Isolated from Electroplating Wastewater Sludge in Japan

The aerobic and rod-shaped FO1 strain of iron-oxidizing bacteria was isolated from electroplating wastewater sludge using colloidal silica plates. Bacterial growth occurred at 25–30°C (optimum temperature, 27°C), pH 2.0–3.5, and in the presence of 1.0–4.0% NaCl. The X-ray diffraction analysis identified the precipitates that were formed during cell growth as jarosite. A biochemical analysis, including the assessments of the whole-cell fatty acids, quinone, and DNA G+C contents, revealed that FO1 was closely related to the genus Acidihalobacter. The 16S rRNA sequence of the FO1 gene was similar to those of the Acidihalobacter prosperus DSM 5130 (97% similarity), Ah. aeolianus DSM 14174 (100%), and Ah. yilgarnensis DSM 105917 (100%) strains. Antibiotic sensitivity tests of strain FO1 revealed that it was tolerant for gentamicin, kanamycin, and tetracycline, whereas it was sensitive to ampicillin and chloramphenicol. Moreover, strain FO1 was able to grow in a microbial electrolysis cell with continuous reduction of Fe³⁺ to Fe²⁺ on the cathode, albeit with a slight inhibition of cell growth. This study provides information regarding the genetics, bioleaching of metals, and electrochemical cultivation of halotolerant iron-oxidizing bacteria in the genus Acidihalobacter.