Bacteria produce chemicals called bacteriocins to kill microbial competitors. These chemicals can serve as natural preservatives by killing potentially dangerous pathogens in food. Lanthipeptides, a class of bacteriocins with especially potent antimicrobial properties, are widely used by the food industry and have become known as “lantibiotics” (a scientific portmanteau of lanthipeptide and antibiotics).

Despite their widespread use, however, little is known about how these lantibiotics affect the gut microbiomes of people who consume them in food. Microbes in the gut live in a delicate balance, and commensal bacteria provide important benefits to the body by breaking down nutrients, producing metabolites, and — importantly — protecting against pathogens. If too many commensals are indiscriminately killed off by antimicrobial food preservatives, opportunistic pathogenic bacteria might take their place and wreak havoc — a result no better than eating contaminated food in the first place.

Effects on good and bad bacteria

A new study published in ACS Chemical Biology by scientists from the University of Chicago found that one of the most common classes of lantibiotics has potent effects both against pathogens and against the commensal gut bacteria that keep us healthy.

Nisin is a popular lantibiotic used in everything from beer and sausage to cheese and dipping sauces. It is produced by bacteria that live in the mammary glands of cows, but microbes in the human gut produce similar lantibiotics too. Zhenrun “Jerry” Zhang, PhD, a postdoctoral scholar in the lab of Eric Pamer, MD, the Donald F. Steiner Professor of Medicine and Director of the Duchossois Family Institute at UChicago, wanted to study the impact of such naturally-produced lantibiotics on commensal gut bacteria.

“Nisin is, in essence, an antibiotic that has been added to our food for a long time, but how it might impact our gut microbes is not well studied,” Zhang said. “Even though it might be very effective in preventing food contamination, it might also have a greater impact on our human gut microbes.”

He and his colleagues mined a public database of human gut bacteria genomes and identified genes for producing six different gut-derived lantibiotics that closely resemble nisin, four of which were new. Then, in collaboration with Wilfred A. van der Donk, PhD, the Richard E. Heckert Endowed Chair in Chemistry at the University of Illinois Urbana-Champaign, they produced versions of these lantibiotics to test their effects on both pathogens and commensal gut bacteria. The researchers found that while the different lantibiotics had varying effects, they killed pathogens and commensal bacteria alike.

“This study is one of the first to show that gut commensals are susceptible to lantibiotics, and are sometimes more sensitive than pathogens,” Zhang said. “With the levels of lantibiotics currently present in food, it’s very probable that they might impact our gut health as well.”

Harnessing the power of lantibiotics

Zhang and his team also studied the structure of peptides in the lantibiotics to better understand their activity, in the interest of learning how to use their antimicrobial properties for good. For example, in another study, the Pamer lab showed that a consortium of four microbes, including one that produces lantibiotics, help protect mice against antibiotic-resistant Enterococcus infections. They are also studying the prevalence of lantibiotic-resistant genes across different populations of people to better understand how such bacteria can colonize the gut under different conditions and diets.

“It seems that lantibiotics and lantibiotic-producing bacteria are not always good for health, so we are looking for ways to counter the potential bad influence while taking advantage of their more beneficial antimicrobial properties,” Zhang said.

The study, “Activity of Gut-derived Nisin-like Lantibiotics Against Human Gut Pathogens and Commensals,” was supported by the GI Research Foundation, the Howard Hughes Medical Institute, the National Institutes of Health (grants R01AI095706, P01 CA023766, U01 AI124275, and R01 AI042135) and the Duchossois Family Institute at UChicago. Additional authors include Chunyu Wu, Ryan Moreira, and Darian Dorantes from the Univeristy of Illinois Urbana-Champaign, and Téa Pappas, Anitha Sundararajan, and Huaiying Lin from UChicago.

Seeing that structure snap open and shut in mere millionths of a second is giving Duke Human Vaccine Institute (DHVI) investigators a new handle on the surface of the virus that could lead to broadly neutralizing antibodies for an AIDS vaccine. Their findings appear Feb. 2 in Science Advances.

Being able to attach an antibody specifically to this little structure that would prevent it from popping open would be key. Their findings appear Feb. 2 in Science Advances.

The moving part is a structure called envelope glycoprotein, and AIDS researchers have been trying to figure it out for years because it is a key part of the virus’ ability to dock on a T-cell receptor known as CD4. Many parts of the envelope are constantly moving to evade the immune system, but vaccine immunogens are designed to stay relatively stable.

“Everything that everybody’s done to try to stabilize this (structure) won’t work, because of what we learned,” said lead author Rory Henderson, a structural biologist who is an associate professor of medicine in DHVI. “It’s not that they did something wrong; it’s just that we didn’t know it moves this way.”

Postdoctoral researcher and study co-author Ashley Bennett offers a play-by-play: As the virus feels for its best attachment point on a human T-cell, the host cell’s CD4 receptor is the first thing it latches onto. That connection is what then triggers the envelope structure to pop open, which in turn, exposes a co-receptor binding site “and that’s the event that actually matters.”

Once both molecules of the virus are bound to the cell membrane, the process of injecting viral RNA can begin. “If it gets inside the cell, your infection is now permanent,” Henderson said.

“If you get infected, you’ve already lost the game because it’s a retrovirus,” Bennett agrees.

The moving structure they found protects the sensitive co-receptor binding site on the virus. “It’s also a latch to keep it from springing until it’s ready to spring,” Henderson said. Keeping it latched with a specific antibody would stop the process of infection.

To see the viral parts in various states of open, closed and in-between, Bennett and Henderson used an electron accelerator at the Argonne National Laboratory outside Chicago that produces X-rays in wavelengths that can resolve something as small as a single atom. But this expensive, shared equipment is in high demand. The AIDS researchers were awarded three 120-hour blocks of time with the synchrotron to try to get as much data as they could in marathon sessions. “Basically, you just go until you can’t anymore,” Bennett said.

Earlier research elsewhere had argued that antibodies were being designed for the wrong shapes on the virus and this work shows that was probably correct.

“The question has been ‘why, when we immunize, are we getting antibodies to places that are supposed to be blocked?'” Henderson said. Part of the answer should lie in this particular structure and its shape-shifting.

“It’s the interplay between the antibody binding and what this shape is that’s really critical about the work that we did,” Henderson said. “And that led us to design an immunogen the day we got back from the first experiment. We think we know how this works.”

This research was supported by the National Institutes of Health (UM1AI14437, R01AI145687, U54AI170752, P30 GM124169, S10OD018483), the Department of Energy (DE-AC02-06CH11357) and the DOE Office of Biological and Environmental Research.