Bacterial Intracellular Sulphur Globules

Abstract

Reduced sulphur compounds such as sulphide, polysulphides, thiosulphate, and elemental sulphur are oxidized by a large and diverse group of prokaryotes. In many cases, intracellular globules of polymeric, water-insoluble sulphur are accumulated either as a transient product en route to sulphate or as the final product. Sulphur globule formation is especially widespread among sulphur-oxidizing Proteobacteria and occurs in purple sulphur bacteria of the family Chromatiaceae, in Beggiatoa species as well as in other “morphologically conspicuous” sulphur bacteria (e.g. Thioploca, Achromatium, Thiovulum). Sulphur globules are typically enclosed by a surface layer consisting of highly repetitive glycine-rich structural proteins (sulphur globule proteins, Sgps) and reside in the bacterial periplasm. Here, an overview of recent findings on the speciation of stored sulphur, the occurrence of Sgps and the enzymes involved in the formation and breakdown of bacterial sulphur globules is given.