Microbial respiration - a biomineral perspective

Microbial biomineralization is a key process in natural and anthropogenic environments. Certain bacteria and archaea produce cellular energy via anaerobic respiration using metals and metalloids as terminal electron acceptors, producing intra- and extracellular biominerals. This article explores the biomineralization of arsenic (As), iron (Fe), sulfur (S) and selenium (Se), in relation with microbial respiratory processes. Ferric iron (FeIII) and the oxyanions of As, S and Se are used as terminal electron acceptors by specialized bacteria and archaea, providing significant amounts of energy under anoxic and nutrient-limiting conditions. These transformations result in the formation of various types of arsenic sulfides, iron (oxyhydr)oxides and sulfides, elemental S/S0 and elemental Se/Se0 biominerals, which will be the focus of this review. Certain biominerals (e.g. S0) function as storage compounds; others, like Se0, may increase the density and the buoyancy of bacteria harboring them or are by-products of this process. Arsenic sulfides and iron (oxyhydr)oxides and sulfides appear to be by-product biominerals or have a yet unknown function. The use of these biominerals as biosignatures is an open topic and an ongoing debate. Further exploration of the reviewed biominerals is needed from both fundamental and applied viewpoints, aspects which will be covered in this review.