“Have you heard of hydrogen sulfide? Even if not, I’m betting you’d recognise the smell. Hydrogen sulfide is the gas responsible for the lovely rotten egg odour that you come across near stagnant waters and in drains.
When certain bacteria degrade sulfur-containing organic matter, they can produce hydrogen sulfide. These are called sulfate-reducing bacteria (SRB) because, well, they reduce sulfate. Reduction is a chemistry term describing the reaction that changes sulfate to hydrogen sulfide.
Sulfate-reducing bacteria are anaerobic, meaning they die when they’re exposed to oxygen. This is why stagnant waters which are not churned up and oxygenated can allow these micro-organisms to bloom and make hydrogen sulfide.
Hydrogen sulfide is well known in the water and oil industries, where it’s a hazard that must be mitigated against. It is highly toxic when inhaled.
Good for our gut
Did you know sulphate-reducing bacteria are also making hydrogen sulfide in your gut? But don’t worry, it’s normal!
In fact, it’s healthy for us to have some hydrogen sulfide gas in our guts. Even our own intestinal cells make small amounts of hydrogen sulfide where it’s used as a signalling molecule.
Sulfate-reducing bacteria live in our guts and make hydrogen sulfide. This is an important process because these bacteria use up hydrogen as part of this reaction. If the bacteria weren’t there to use up the hydrogen, microbial fermentation in our guts would come to a stop. This is because hydrogen is a natural product of the fermentative process, and like many chemical reactions in biology, the reaction is kept under a careful balance where the reaction flows nicely from substrates to products when the products are maintained at a low level.
If these hydrogen-utilising bacteria weren’t there, the partial pressure of hydrogen would increase and eventually prevent the fermentation reaction. This would be bad news because we need the good bacteria in our guts to ferment the fibre we provide them, as they make all sorts of important, health-promoting compounds like short chain fatty acids which keep our gut healthy. Sulfate-reducing bacteria are part of the normal gut microbiota in humans.
I work with one specific sulfate-reducing bacteria (SRB) called Bilophila wadsworthia. Although SRB and Bilophila wadsworthia are not well known and only make up a small proportion of the bacteria in our guts, we shouldn’t underestimate their importance!
Diseases associated with Bilophila wadsworthia
Bilophila wadsworthia was discovered in the 1980s, when it was found in people who had severe appendicitis. The researchers found that it grew really well in bile – the genus name “Bilophila” means “bile-loving”, and the original isolations were performed at the Wadsworth Veterans Administration Medical Center in the USA, hence the species name “wadsworthia”.
Since then, there has been a buzz of research associating Bilophila wadsworthia with negative effects in the gut, where it has been linked to inflammatory diseases like Inflammatory Bowel Disease, Irritable Bowel Syndrome, and colorectal cancer.
The balance of bacteria in the gut
But is Bilophila wadsworthia a real baddie, or just misunderstood? Despite being associated with inflammation, we know that Bilophila wadsworthia is present in the guts of most healthy people. 50-60% of us have Bilophila wadsworthia in our guts and it is part of the normal, varied mix of bacteria that make up our microbiota.
We think the differences between Bilophila wadsworthia in health and disease could be down to how much Bilophila grows, and how much hydrogen sulfide it makes.
In small amounts, it seems like Bilophila could be a helpful member of the gut microbiota, making a little hydrogen sulfide that helps prevent harmful disease-causing bacteria from getting settled in, whereas if Bilophila grows too much or makes too much hydrogen sulfide, it could trigger inflammation in the gut.
My research is working to understand how Bilophila’s growth and hydrogen sulfide production is affected by different factors, like diet, and the other bacteria present in our gut microbiota. If we know what factors are important for triggering Bilophila wadsworthia to grow more or make more hydrogen sulfide, we can use targeted prevention which could help us control and prevent inflammatory diseases in the gut.”