A nitrogenase-like enzyme system catalyzes methionine, ethylene, and methane biogenesis

Soil sulfur metabolism surprise Soil bacteria have a range of metabolic pathways that contribute to acquiring and recycling nutrients and carbon. Curiously, some of these organisms give off ethylene gas when starved for sulfur under anaerobic conditions. North et al. traced the source of ethylene to a small, sulfur-containing organic molecule produced by certain reactions in cells. Growing cells in sulfur-limiting conditions enabled them to identify the enzymes involved in sulfur salvage, and the concomitant ethylene production, through this pathway. Methane and ethane were also observed as products when appropriate substrates were provided. The key genes involved are distantly related to nitrogenase and several other reductase enzymes found in bacteria and archaea. The involvement of such nitrogenase-like genes in sulfur metabolism highlights the potential of unexplored diversity in this family of enzymes and raises many mechanistic and evolutionary questions that are now ripe for exploration. Science , this issue p. 1094