Imagine living in a city made of similar apartment buildings. You and your fellow residents exist happily in your own buildings, making everything that you need to sustain yourselves. Sometimes you take notes from your neighbors on recipes or instructions on using the things around you. Everything is peaceful until the drop-off of things that cannot be made at home. Pandemonium and chaos ensue, as you compete over a resource that you rely on, but cannot produce.
According to new research from the University of Illinois School of Molecular & Cellular Biology, a similar arrangement could be happening in the human gut microbiome, with the transport of vitamin B12—one type of large corrinoid molecules. Katie Frye, a PhD candidate in microbiology, studies the dynamics of a group of common human gut microbes called Bacteroidetes through mobile genetic elements.
In a new publication, Frye et al. uncover some of the mystery of the process surrounding the transport of massive corrinoid molecules that are not synthesized by the bacteria within the gut. Her findings are detailed in “Mobilization of vitamin B12 transporters alters the competitive dynamics in a human gut microbe,” in the journal Cell Reports.
Bacteroidetes are just one type of microbe that make up the entire gut microbiome. Bacteria can exchange information with each other in the form of mobile genetic elements that are traded between individual bacteria. Antibiotic resistance is an example of a beneficial trait commonly carried on mobile genetic elements exchanged between bacteria.
Since gut microbes can share the mobile genetic element that allows them to acquire vitamin B12 from the environment, when a new bacterium acquires the element, they can now use vitamin B12 within the bacterial cell in processes such as amino acid synthesis, nucleotide synthesis, and metabolism. However, vitamin B12 itself is a very limited resource since it cannot be produced by the Bacteroidetes, so they must compete very intensely against each other.
“It's really novel that we've found a group of mobile genetic elements in a really prominent member of the human gut [microbiome] and that they are a beneficial mobile genetic element,” Frye said. “We don't think of [these elements] like that very often because they don't care what they're doing. But to be successful, they have to benefit their hosts, the bacteria. Usually, they do that by providing antibiotic resistance genes … But in this case, they're sharing an import system for an important vitamin that makes them able to colonize [the] host, which is really exciting. It’s beneficial to them and it’s beneficial to us because these are beneficial microbes.”
When Frye and fellow researchers began their work, “we didn’t even know it was a mobile genetic element at the start of this.” She asked herself “Is it a mobile genetic element? Does it move? What does it move? Who does it move it to?” These questions were tested in the experimental techniques described in the paper.
Although Frye, as a microbiologist, isn’t looking at this class of mobile genetic elements specifically in terms of human health, her research does potentially impact our understanding of the bacterial communities in our bodies. For example, humans cannot synthesize vitamin B12 and must ingest it through animal-based foods like meat and eggs or through supplements and fortified foods. There are other molecules that we and our gut microbiomes need to survive that are not produced in the gut itself, making efficient absorption and metabolic distribution of those molecules necessary.
Following this work, Frye is interested in investigating the preferences that these transporters might have for different molecules and environments. Learning more about the conditions that influence the competition for this essential resource in Bacteroidetes could also show researchers better combinations of transporters and molecules, and could expand into research into the other types of bacteria in the human gut.
