“Selenospirillum indicus” is the first cultured species of the proposed new genus “Selenospirillum“, and the sequencing of its genome will expand the range of experimental approaches that researchers can use to characterize its metabolic pathways for energy production and understand how these pathways are regulated. “S. indicus” is notable for its ability to reduce selenate to selenite and further to insoluble elemental selenium, in a process called dissimilatory selenate reduction.
Selenospirillum indicus strain S5. Micrograph courtesy Elisabetta Bini.
Selenium in the environment exists as selenate (+6) and selenite (+4), which are most soluble; elemental selenium (0), a solid; and selenide (-2), which is gaseous. Various physical, chemical and biological reactions facilitate the conversion of selenium from one form to another, mediating the cycling of selenium in nature. Although physical processes such as dissolution, volatilization, and adsorption contribute to abiotic transformations, the biogeochemical cycling of selenium in the environment is predominantly governed by microorganisms, which play an important role in oxidation, reduction, methylation and volatilization. Knowledge of how this process of speciation takes place is relevant to studies aimed to develop processes for removal of selenium from polluted soils, and therefore relevant to environmental science and toxicology studies. Studies of the microbial speciation of the metalloids selenium and arsenic are also fundamental to the elucidation of how their role as terminal electron acceptors currently affects geochemical cycles and to what extent this has contributed to determine the chemical composition of Earth.
However, even close to two decades after the first description of a novel dissimilatory selenate respiration pathway, we know very little about this process and the microorganisms harboring this metabolic capability. What contributes or drives the existence of these organisms in nature is a challenging and intriguing question. Genomic analysis and biochemical characterization of the selenate reductase enzymes from these bacteria will shed some light on the evolution of this respiratory process.
Principal Investigators: Elisabetta Bini and Max Haggblom (Rutgers Univ.)