Metalloproteins and enzymes are an essential part of all respiratory electron-transfer chains and provide a pathway for electron transfer to terminal electron acceptors. Since bacteria can utilize a wide range of respiratory substrates, this variety of potential electron acceptors has facilitated the need for many different respiratory metalloproteins. Bacterial selenate respiration requires the sequential reduction of the selenium oxyanions selenate and selenite resulting in the precipitation of elemental selenium. The initial bioenergetic processes of selenate respiration are driven by metalloproteins utilizing cofactors containing iron and molybdenum. However, the assembly of the elemental selenium into selenium nanosphere crystals has shed light on a new family of proteins involved in selenium biomineralization. This article highlights some of the recent advances in our understanding of selenate respiration in the bacterium Thauera selenatis, with particular focus on the metalloproteins involved in selenate reduction and the novel proteins that function to deal with these insoluble selenium deposits. “As mineralogy constitutes a part of chemistry, it is clear that this arrangement of minerals must derive its principles from chemistry” Jöns Jacob Berzelius 1814

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