For generations, the human body's hormonal landscape was mapped without accounting for its microbial inhabitants. Now, researchers have identified a bacterium residing in the urinary tract — Actinobaculum massiliense — that carries the molecular machinery to convert a naturally occurring steroid into testosterone, a hormone long understood as central to prostate biology. The discovery, published in Nature Communications and built on contributions from multiple American universities, does not rewrite what we know about prostate cancer, but it quietly expands the territory of what we must ask: w