timeThe intestines provide abundant nutrients to intestinal bacteria. In addition to ingested food, glucocorticoids in bile are important substrates for microorganisms. Bacteria can convert these steroids into various metabolites that affect the host system.1 In a recently published study cellResearchers have shown that some gut bacteria can produce sex hormones, including progesterone.2 Researchers have previously shown that progesterone regulates the menstrual cycle and pregnancy and alters neuronal activity. This study marks the first report of bacterial production of progesterone.
To isolate bacteria capable of converting glucocorticoids into sex hormones, the researchers cultured human stool samples on agar plates.
Megan McCurry, Electron Microscopy Facility, Harvard Medical School
“I’ve always been surprised by the extent of the impact of gut microbes on the host, but maybe I shouldn’t be anymore,” says Gerald Clark, a neurobiologist at University College Cork with an interest in the gut-brain axis.
For most of her education, Sloan Devlin trained to be a chemist. However, as a postdoctoral researcher in a lab that studies host-microbiome interactions, she saw an opportunity for someone with a chemistry background to elucidate the effects of bacterial molecules on the host. “Some chemists prefer physical science and materials science, and some chemists prefer biology,” Devlin said. “I was always more interested in biology.” Now, in his lab at Harvard Medical School, Devlin is trying to understand the mechanisms by which gut bacteria influence neurological function and behavior.
While browsing the literature for information on how gut bacteria metabolize glucocorticoids, the authors realized that there had been virtually no new data on the topic since the early 1980s—a 40-year gap in knowledge. Some researchers report that gut bacteria can convert these molecules into sex hormones. However, because these studies were conducted before the advent of modern genetics, there is no information about the bacterial strains or genes involved in the process. At the time, researchers needed 5 to 50 milliliters of bile to extract a few microliters of steroids.3 Due to strict patient protection regulations, it is no longer possible to obtain such large quantities of drugs from patients. Therefore, Devlin had to develop a technique to extract and measure biomolecule levels from the limited and precious bile.
To do this, Devlin teamed up with study co-author Megan McCurry, a microbiologist at the biotech company Holobiome. McCurry spent five years developing a highly sensitive chromatography technique that requires 500 times less bile than previous assays. Her technique has also proven effective at isolating and quantifying steroids, which are so potent that they are present in minute quantities.
Using improved techniques, McCurry discovered that certain glucocorticoids are more abundant in human bile than others. The authors were most interested in a group of glucocorticoids that are converted into progestins, a class of sex hormones.
To determine whether gut bacteria could carry out this chemical reaction, the researchers collected feces from mice with and without gut bacteria and cultured the samples with glucocorticoids. Feces is representative of the gut microbiome and its products. Devlin and her team only observed progesterone in the feces of mice with gut microbiota, suggesting that bacteria play a key role in producing the hormone.
exposed Eggella tarda The bacteria convert hydrogen gas (in the yellow balloon) causing them to produce progesterone from glucocorticoids.
Megan McCurry, Electron Microscopy Facility, Harvard Medical School
Devlin wanted to isolate the bacterial species responsible for converting glucocorticoids into progesterone. According to previous research, this species Eggella tarda To be able to carry out this reaction, Devlin and her team tested various strains of bacteria. However, they never observed progesterone production. So Devlin and her team decided to isolate the species from human feces. They cultured human feces with an amino acid that stimulates bacterial growth. Slow Eucalyptus and its microbial relatives, and look for progesterone-producing bacteria. Although the human gut microbiome contains 300 to 500 different species of bacteria, there is only one, Gordonii bacilli, Got the job done, albeit poorly.4 However, when they grow up pameleaco with intestinal symbionts E. coli Nissle 1917 (EcN) This significantly increases progesterone production. Twelve other bacterial strains from the same family—Eggellaceae—The ability to produce progesterone is acquired when co-cultured with EcN.
It was clear that EcN was essential for chemical reactions, so Devlin hypothesized that it could create favorable conditions for progesterone production in one of three ways: lowering the redox potential of the medium required for the reaction, interacting physically with other bacteria interaction For synergistic metabolism, or the release of extracellular substances that promote bacterial activity.
They tested each scenario using E. Slow, relatives pameleaco Scientists can genetically modify it. After disproving the first two theories, the team had an eureka moment. When testing the effects of extracellular preparations, they extracted the supernatants of EcN cultures and filtered them to remove dissolved gases. However, for some cultures, they skip this step. When they added the supernatant to Slow Eucalyptus In cultures, the authors only observed progesterone production when the bacteria were exposed to dissolved gases. Since hydrogen is dominant in the gut and is produced by EcN, Devlin suspects it may be key for bacteria to convert glucocorticoids into progesterone. To test this, they added hydrogen gas Slow Eucalyptus and similar amounts of progesterone production were observed.
“We all fart, right?” Devlin said. “But we found that this hydrogen production actually induces bacterial metabolism of the steroid, which to me was the most surprising thing about this work.”
Researchers took an image EggellaEnta and E. coli Nissel Co-cultures using electron microscopy.
Megan McCurry, Electron Microscopy Facility, Harvard Medical School
Next, through comparative genomics analysis of the genomes of progestin-producing and non-progestin-producing bacterial strains, Devlin and her team identified four gene clusters involved in this response. Expressing this cluster in a bacterial species that is unable to convert glucocorticoids into progesterone enables it to do so.
“This is the kind of work the field needs right now,” Clark said. “We have many observations of microbes doing specific things to affect their hosts, but we lack solutions to intervene and tweak things to our advantage.”
Other research groups have shown that levels of certain progesterone-producing glucocorticoids are 5 to 10 times higher in pregnant women.3 Using stool from pregnant and non-pregnant women, Devlin and her team found that increased glucocorticoid concentrations led to increased progesterone levels, which were twice as high in pregnant women.3 enriched pameleaco, Slow Eucalyptus, Gene clusters in these samples strongly suggest that the microbiome contributes to high levels of progesterone.
To further explore how the microbiome produces higher levels of progesterone during pregnancy, the team transplanted feces from pregnant mice into non-pregnant female mice without a microbiome and detected high levels of progesterone in the recipients’ feces. Progesterone. Only these mice were transplanted Slow Eucalyptus and EcN produced the same results.
“One of the hallmarks of our work is that it raises more questions than it answers,” Devlin said. She is interested in looking at longitudinal samples throughout pregnancy to uncover the relationship between the gut microbiome and rates of postpartum depression. Unfortunately, Devlin noted, fecal sample biobanks are difficult to obtain. “My message to clinicians is: Consider collecting the patient’s stool,” Devlin said.
