Thiosulfate (S2O32−) (IUPAC-recommended spelling; also thiosulphate in British English) is an oxyanion of sulfur. The prefix thio- indicates that thiosulfate ion is a sulfate ion with one oxygen replaced by a sulfur. Thiosulfate has a molecular shape known as tetradehral. Its Point group is C3v. Thiosulfate occurs naturally and is produced by certain biochemical processes. It rapidly dechlorinates water and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate is also useful in smelting silver ore, in producing leather goods, and to set dyes in textiles. Sodium thiosulfate, commonly called hypo ("Hyposulfite"), was widely used in photography to fix black and white negatives and prints after the developing stage; modern 'rapid' fixers use ammonium thiosulfate as a fixing salt because it acts three to four times faster. Some bacteria can metabolise thiosulfates.