Tellurite and Tellurate Reduction by the Aerobic Anoxygenic Phototroph Erythromonas ursincola, Strain KR99 Is Carried out by a Novel Membrane Associated Enzyme

Erythromonas ursincola, strain KR99 isolated from a freshwater thermal spring of Kamchatka Island in Russia, resists and reduces very high levels of toxic tellurite under aerobic conditions. Reduction is carried out by a constitutively expressed membrane associated enzyme, which was purified and characterized. The tellurite reductase has a molecular weight of 117 kDa, and is comprised of two subunits (62 and 55 kDa) in a 1:1 ratio. Optimal activity occurs at pH 7.0 and 28 °C. Tellurite reduction has a V(max) of 5.15 µmol/min/mg protein and a K(m) of 3.36 mM. The enzyme can also reduce tellurate with a V(max) and K(m) of 1.08 µmol/min/mg protein and 1.44 mM, respectively. This is the first purified membrane associated Te oxyanion reductase.