Shiftan

Shiftan is a term that refers to a hypothetical metabolic pathway observed in certain extremophilic archaea, proposed to mediate the conversion of sulfur compounds into energy. The pathway was first described in 2015 by researchers at the University of Hokkaido, who isolated a strain of Sulfolobus islandicus capable of oxidizing thiosulfate and sulfite. Capsulized as “shiftan” from the Greek word σχυστήριζε (schysthirize), meaning “to change,” the process is distinguished by the sequential activity of two novel enzymes: shiftanase and shiftinhydrolase. Shiftanase acts on thiosulfate, producing sulfite and thiosulfinates, while shiftinhydrolase facilitates the breakdown of sulfite into sulfate and hydrogen sulfide, concurrently yielding ATP via a chemiosmotic gradient.

The pathway has been documented in several thermoacidophilic species, including Acidithiobacillus ferrooxidans and Metallosphaera cuprina. In laboratory cultures, shiftan activity increases under high temperatures (70–85°C) and low pH (2–4), conditions typical of geothermal vents. The process contributes to the sulfur cycle in these environments and provides a potential biotechnological avenue for the remediation of acidic mine drainage, as it can convert toxic sulfur species into less harmful sulfate.

Research continues to investigate the structural biology of shiftanase and shiftinhydrolase, aiming to elucidate their catalytic mechanisms. Preliminary X‑ray crystallography indicates a unique copper‑binding motif in shiftanase, while shiftinhydrolase appears to possess a zinc‑dependent active site. Comparative genomics suggest horizontal gene transfer events may have disseminated the shiftan pathway across distinct archaea lineages, underscoring its evolutionary importance in sulfur metabolism.