MSU Team Uncovers How Staph Bacteria Adjust Their Sulfur Diet

The human body fights staph infections by starving the bacteria of essential nutrients, but Staphylococcus aureus—the agent behind MRSA and most staph infections—is remarkably good at changing its diet. S. aureus needs sulfur to build proteins and other materials essential for survival, and a new Michigan State University study, published in the Journal of Bacteriology, found the bacterium can adjust its diet depending on what sulfur sources remain available. Understanding how it finds the nutrients it needs could eventually reveal new ways to weaken the bacterium, potentially making antibiotic-resistant infections easier to treat.

The team, overseen by Neal Hammer found that S. aureus adjusts its inner workings in response to several sulfur-containing compounds, such as cysteine, glutathione or thiosulfate. “Many people think of bacteria as simple organisms, but this study shows that S. aureus can effectively “change its diet’ depending on what’s available,” Hammer said. “It monitors its environment, activates different genetic programs and switches between nutrient sources to keep growing.”

Earlier work showed that a regulator protein called CymR controls much of this behavior, keeping sulfur-acquisition genes off until the bacteria’s supply runs low. The new study found that starved bacteria switch on hundreds of genes, far more than CymR controls, also triggering related pathways like iron acquisition and oxidative stress defenses. Thiosulfate stood out among the sulfur sources tested, triggering far more gene activity than the others and helping the team identify a transporter protein the bacteria use to grow on it. “When staph infects people, it’s basically eating us,” Hammer said. “But the question is: what’s on the menu? These studies get us closer to understanding not only staph, but also the metabolites that change within our bodies in response to infection.”

The team also found that some sulfur compounds give the bacteria more than nutrition. Glutathione helped shield the bacteria from toxic forms of iron and from hydrogen peroxide, which the immune system uses against invading microbes. “Sulfur is not simply food for the bacterium,” Hammer said. “The same sulfur-containing molecules that provide nutrients also help protect the cell from potentially lethal stresses. In other words, the bacterium uses sulfur both as fuel and as armor.”

Next, the team plans to determine which sulfur sources S. aureus relies on during real infections, and whether blocking its access could make infections easier for the immune system, or antibiotics, to clear. As antibiotic resistance spreads, understanding how S. aureus feeds itself gives researchers one more piece of the puzzle in the search for new ways to fight it.