Researchers have identified a urinary tract bacterium capable of converting the steroid precursor DHEA into testosterone under laboratory conditions, revealing a previously unknown microbial pathway that could impact prostate biology, according to a study supervised by Jason M. Ridlon.
The finding does not indicate that the bacterium causes prostate cancer or that the microbial testosterone reaches tumors. Instead, it demonstrates that microorganisms living near the prostate possess the molecular machinery to produce hormones central to prostate biology, according to the research team.
The Urinary Microbiome and Steroid Transformation
Urine was long assumed to be sterile, leaving the urinary tract out of the original Human Microbiome Project. Scientists now recognize a distinct community of microorganisms known as the urinary microbiome, or urobiome.
To determine what these microbes actually do, researchers examined bacteria isolated from urine samples collected from men before prostate biopsy. The team developed a rapid screening method called the Human Sterolbiome Discovery High-throughput assay, or HSDH assay, to identify organisms capable of transforming steroids, according to the study.
Among the identified organisms was Actinobaculum massiliense. When supplied with DHEA, or dehydroepiandrosterone—a steroid naturally produced by the human body—the bacterium produced intermediate steroid molecules and ultimately testosterone.
"The urinary microbiome has often been studied by asking which organisms are there," said Jason M. Ridlon, who conceptualized and supervised the study. "We wanted to understand what those organisms are capable of doing. Identification of this androgen-generating mechanism supplies researchers with distinct genes and enzymes ready for evaluation regarding urinary wellness and pathology."
Decoding Enzyme Mechanics Through 3D Modeling
After confirming the testosterone-producing ability of Actinobaculum massiliense, the research team searched its genome and identified two candidate genes named dirA and dirB, for DHEA isomerase reductase.
Laboratory experiments showed that DirA performed several different steroid transformations to reach testosterone through multiple routes. DirB performed only part of that chemistry. To solve this puzzle, researchers at Auburn University generated three-dimensional models of DirA and DirB to simulate molecular movements.
Bernardi’s group used atom-by-atom movies to show enzymes flexing and steroids rotating over time. According to the computational study, DirA features a broad, open pocket that gives steroids room to move and reposition. DirB contains a narrower internal tunnel that frequently leaves the steroid flipped or misaligned.
"At this scale, chemistry depends on choreography," said Rafael Bernardi, associate professor in Auburn University’s Department of Physics and co-author of the study. "The steroid has to be in the right place, facing the right way, at the right moment. One enzyme gives it room to do that. The other does not."
Working alongside Bernardi, doctoral candidate Raissa Rosa from Bernardi’s laboratory carried out the computational research and built the catalytic models by combining artificial intelligence-based protein modeling with atom-by-atom simulations.
"A static structure can show us that a molecule fits inside a protein," Rosa said. "Through simulations, we can determine whether it achieves the exact spatial orientation required for the reaction and if that configuration stays secure."
Implications for Prostate Cancer and Diagnostics
Because advanced prostate cancer treatments often attempt to reduce testosterone production or block its effects, the discovery of a microbial testosterone pathway introduces new questions for researchers.
"We are not saying that these bacteria cause cancer," Bernardi said. "What we now know is that they possess the molecular machinery to produce testosterone. Because prostate cancer is so closely connected to androgen signaling, that is something worth understanding."
Scientists must now determine whether this pathway remains active inside the human body, how much androgen bacteria can produce locally, and whether those molecules reach nearby tissue. Researchers can now search urinary microbiome datasets for dirA and dirB to examine whether their presence correlates with differences in urinary hormones, prostate conditions, or treatment responses.
Beyond oncology, the findings may affect how medical researchers interpret urinary steroid profiles used in diagnostics and performance-enhancing drug testing, as microbial metabolism within the urinary tract could alter baseline compounds.
Collaborators on this project hailed from Auburn University, the University of Illinois Urbana-Champaign, Carle Foundation Hospital, and Virginia Commonwealth University.
Did You Know?
Historically, experts assumed urine lacked any bacteria, and the original Human Microbiome Project omitted the urinary tract entirely.
Frequently Asked Questions
Does this bacterium cause prostate cancer?
No. The study shows only that the urinary bacterium Actinobaculum massiliense possesses the molecular machinery to produce testosterone from DHEA in a laboratory setting. Researchers have not proven that this microbial testosterone reaches tumors or alters disease progression.
What do the genes dirA and dirB do?
These genes encode enzymes called DHEA isomerase reductases. DirA features a flexible pocket that allows steroids to move and undergo multiple transformations to form testosterone, while DirB has a restricted tunnel with limited catalytic capabilities.
How was this discovery made?
Researchers combined patient urine samples, bacterial culturing, genomic sequencing, analytical chemistry, protein biochemistry, and AI-supported computational simulations to identify the pathway and map the physical motion of the enzymes.