While the aforementioned physiological reactions are utilized for TeO32− resistance and/or reduction, none involves a specific tellurite reductase. Our understanding of how bacteria carry this out is limited. Unlike for selenate resistance/reduction, where specific reductases have been identified, such in cells of Thauera selenatis , only a single example of a tellurite specific reductase has been isolated to date from the Bacillus sp. STG-83 . Although not proven, this bacterium might be capable of dissimilatory anaerobic reduction, therefore, the enzyme is likely respiratory in nature. Investigation into the strategies for tellurite reduction has just begun to expand. Recently, several bacterial species have been isolated that are highly resistant to tellurite (up to 2700 µg/mL) . Among bacteria possessing very high level resistance are aerobic anoxygenic phototrophs (AAP) isolated from extreme environments . This group of bacteria seems to have evolved an inherent ability to deal with this oxyanion. Therefore, we set forth to investigate the physiological and metabolic effects of TeO32− on cells, factors affecting reduction, and differences in expression of a reducing system by AAP inhabiting extreme environments. Species chosen were Erythromicrobium ezovicum (strain E1), Erythromicrobium hydrolyticum (E4(1)), Erythromicrobium ramosum (E5), Erythromonas ursincola (KR99), Sandaracinobacter sibiricus (RB 16-17), and Roseococcus thiosulfatophilus (RB3). All are freshwater bacteria from cyanobacterial mats developed around thermal springs in the Baikal Lake region in Russia . They reduce very high levels of tellurite to elemental Te under aerobic conditions .