Is nitrogen fixation good for the gut? Dr Lizbeth’s Sayavedra’s fellowship
11th October 2024
We speak to Dr Lizbeth Sayavedra about her BBSRC Fellowship investigating nitrogen fixation in the gut
“Nitrogen is key to life. Most nitrogen exists in the form of N2, dinitrogen, but we cannot use this form of gaseous nitrogen in the air. Most organisms get nitrogen through their food.
There are a few organisms, like leguminous plants, that have evolved close relationships with symbiotic bacteria that can fix nitrogen for the plants, converting it into ammonia. This ammonia is then converted into amino acids, which the plant can use.
During my postdoctoral research at the Quadram Institute, I found that there is a bacterium in the human gut that is capable of converting nitrogen into ammonia and then into amino acids. The bacterium belongs to a group of bacteria called suphate-reducing bacteria which respire sulphate and convert it into hydrogen sulphide.
I have recently been awarded a BBSRC fellowship to focus on these sulphate-reducing bacteria and their impact on nitrogen fixation within the gut.
Through my fellowship, I will explore whether these nitrogen-fixing bacteria can be used as an additional source of protein in the long-term, particularly in groups that struggle to get enough protein such as the elderly and infants.
The idea is that if the nitrogen-fixing bacteria do increase protein content in the gut, the bacteria could potentially be used as a probiotic to boost protein.
Is nitrogen fixation good for the gut?
In my fellowship, I aim to determine when nitrogen fixation can happen in the gut and find out whether this is good or bad for the gut.
I will be using labelled isotopes of nitrogen, to see if bacteria share the nitrogen they fix and if this nitrogen is shared with the microbiome and the host. I have a collaboration with Professor Manuel Kleiner and Ayesha Awan at North Carolina State University in the US. They will be doing metaproteomics and stable isotope proteomics to track the nitrogen incorporation into protein. Through a BBSRC’s International Partnership award, I have been to the US to learn about the techniques and discuss the future of our collaboration.
The nitrogen-fixing bacteria might not just be helping the human host by directly helping to make proteins but also by increasing the abundance of other members of the microbiome that are beneficial. This could be another way nitrogen-fixing bacteria contribute to the overall health of the host.
As well as fixing nitrogen, the bacteria also produce hydrogen sulphide. Hydrogen sulphide is important for cell signaling but in high concentrations, it can be detrimental to the gut and break down the intestinal barrier. I will be looking at how this impacts the gut.
Comparing nitrogen fixation in the gut of vegetarians compared to omnivores
I will be comparing the gut microbiomes of vegetarians to omnivores to understand whether nitrogen fixation is good for the gut, and how this impacts hydrogen sulphide production.
The process of nitrogen fixation is very expensive energetically, so bacteria prefer to take nitrogen that’s already there rather than producing it themselves through nitrogen fixation. So, when there is a high concentration of nitrogen, we expect there will be less nitrogen fixation.
Generally, vegans and vegetarians consume less protein. I hypothesise that vegans and vegetarians therefore will likely have a higher rate of nitrogen fixation compared to omnivores, because they are consuming less protein.
In the lab I will be doing in vitro colonic incubations to measure the rate of nitrogen fixation to test this hypothesis.
Mussels, microbiomes and metabolism; path to independent research
I became interested in host-bacterial interactions when I was studying at university.
Symbiosis is a long-term biological interaction between two or more different species, or symbionts, that live in close proximity. I’ve worked with lots of different organisms but what has always fascinated me is how bacteria can help with the nutrition of their host.
First, I started studying insect symbioses, then I moved on to mussels.
Deep-sea mussels have a nutritional symbiosis with bacteria which is highly specific. The bacteria oxidize reduced compounds, such as hydrogen sulphide, that emerge from the sea floor, using them as an energy source. These microbes are known as sulphur-oxidising bacteria.
Deep sea mussels and the human gut microbiome sound very far apart but in reality, they share a lot of metabolic pathways.
I joined Professor Arjan Narbad’s group at Quadram Institute in 2017 to work on sulphate-reducing bacteria in the human gut microbiome. Arjan has been my mentor since I started at the Quadram Institute. It’s always good to have a great mentor that can help support you.
Applying for the BBSRC fellowship was a long process. I think the Quadram Institute is really good at supporting fellowship applications. We have an internal committee, that helps support fellowship applications. The committee members were helpful and gave constructive feedback about my proposal. Our Contracts team helped with the budgeting too.
The BBSRC Fellowship has given me the opportunity to be more independent, take the lead of my projects and build my own research niche. I’m looking forward to learning more about nitrogen fixation in the gut and the potential impact on our health.
Related People
Related Research Groups
Arjan Narbad
Related Research Areas
Food, Microbiome and Health