Introduction to Sulfur Metabolism in Phototrophic Organisms

Abstract

Sulfur is one of the most versatile elements in life due to its reactivity in different oxidation and reduction states. In phototrophic organisms, the redox properties of sulfur in proteins and of sulfur-containing metabolites are particularly important for the mediation between the reductive assimilation processes of photosynthesis and reactive oxygen species that arise as by-products of electron transport chains in chloroplasts and mitochondria. Further, reduced sulfur compounds play a prominent role as electron donors for photosynthetic carbon dioxide fixation in anoxygenic phototrophic sulfur bacteria. The assimilatory process is part of the biological sulfur cycle that is completed by dissimilation of reduced sulfur compounds. In contrast to the assimilatory provision of sulfur-containing cell constituents that is found in most taxonomic groups, dissimilation is restricted to prokaryotes and serves energy-yielding processes where sulfur compounds are donors or acceptors of electrons. Interest in the investigation of the multiple functions of sulfur-related processes has exponentially increased in recent years, especially in molecular and cellular biology, biochemistry, agrobiotechnology and ecology.