Sulfur is the silent engine driving life, decay, and the chemistry of our planet.

Nature · Published 3 October 2026 Swipe more like this →

In short: Sulfur is essential to all living matter, acting as a vital component of proteins and amino acids. Beyond biology, this element cycles through Earth's soil, water, and atmosphere, driven by microbial transformations that convert complex remains into usable nutrients. It is a fundamental, yet often invisible, pillar of global ecology.

At the heart of the sulfur cycle lies a complex series of microbial transformations. Microorganisms, a diverse group including bacteria and fungi, are responsible for breaking down organic matter and recycling it into simpler substances. This process is crucial for life, as sulfur is a necessary building block for proteins. In the soil, these microbes facilitate the conversion of organic sulfur into sulfates, which plants can then absorb and utilize for growth.

The movement of sulfur is not limited to the terrestrial realm; it is a global biogeochemical process. Sulfur shifts between rocks, waterways, and living systems, existing in various oxidation states. While the biosphere relies on sulfur for biological function, it does not act as a primary sink. Instead, the vast majority of the planet's sulfur is sequestered in sedimentary rocks or dissolved in the oceans as sulfate. These oceanic sulfates serve as critical electron acceptors for microorganisms inhabiting anoxic waters.

Human activity and geological events have significantly altered the natural sulfur balance. Historically, volcanic activity and the weathering of the Earth's crust were the primary drivers of sulfur mobility. Today, the burning of fossil fuels introduces substantial amounts of sulfur dioxide into the atmosphere, acting as a pollutant. In the distant past, similar large-scale releases—triggered by igneous intrusions into coal measures—are believed to have disrupted the climate system, potentially contributing to the Permian-Triassic extinction event.

Microbes remain the most influential actors in this cycle, whether they are mineralizing organic sulfur or mediating the oxidation and reduction of sulfur compounds. Their ability to thrive in diverse environments—from the guts of animals to the depths of the ocean—ensures that sulfur continues to circulate. By understanding these microbial mechanisms, scientists gain insight into how life sustains itself and how the Earth’s chemical composition has evolved over geological time.

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