Abstract

Sulfur-based respiration has been proposed to be one of the earliest energy conserving pathways for life on earth, and the pathway remains important to the sulfur cycle in oceans, the atmosphere, sediments and the deep subsurface, and is inextricably linked to the other elemental cycles on the earth. In microbiology, elemental sulfur has generally been assumed to take the form of either insoluble S8 or soluble polysulfide (Sn2-)/sulfide (S2-). In reality, however, sulfur can form a range of different allotropes and can come in the form of particles with very different sizes and characteristics, the speciation of which can control availability to microbes, enzymes, and abiotic reactants. We’ll discuss the ways in which sulfur may be made biologically available (and how we can detect those different forms of S), how enzymes that react with S-containing compounds catalyze their chemistry, and how one can analyze the complex microbial communities involved in reactions such as sulfur cycling.