Chapter 21.4, Problem 1CR

Bacteria play major roles in both the oxidative and reductive sides of the sulfur cycle. Sulfur- and sulfide-oxidizing bacteria produce ${\text{SO}}_4{}^{2-}$, whereas sulfate-reducing bacteria consume ${\text{SO}}_4{}^{2-}$, producing H₂S. Because sulfide is toxic and reacts with various metals, ${\text{SO}}_4{}^{2-}$ reduction is an important biogeochemical process. Dimethyl sulfide is the major organic sulfur compound of ecological significance in nature.

Q    If sulfur chemolithotrophs had never evolved, would there be a problem in the microbial cycling of sulfur compounds? What impact would coastal marine eutrophication have on microbial sulfur transformations?