More clues reveal how gut bacteria works

As you enjoy your various holiday meals this season, don’t forget to thank your resident bacteria. 

Amazingly, many of the carbohydrates that you eat, from veggies to wheat bread, aren’t broken down by your own cells but by certain microbes that live in the gut.

Now research from the University of Michigan uncovers a unique way the bacteria Bacteroides, which make up nearly half of the gut microbiome, synthesize the proteins needed to degrade carbohydrates.

"Bacteroides are super important for processing those carbohydrates, and when they do that, they don't actually release the sugars back into the intestine, but take all those sugars, ferment them, and then release short-chain fatty acids, which have all sorts of different physiological effects,” said Nicole Koropatkin, Ph.D., associate professor in the Department of Microbiology and Immunology.

Short-chain fatty acids, like propionate and butyrate, are linked to overall gut health and can reduce inflammation.

To make short-chain fatty acids, bacteria first decorate their cell membranes with proteins called lipoproteins, with the lipid tethering the protein to the cell like the string on a balloon. 

This technique is well documented in E. coli bacteria, which uses an enzyme called lipoprotein N-acyltransferase. 

However, this process in Bacteroides wasn’t yet described.

Krista Armbruster, Ph.D., a bacterial geneticist working with Koropatkin, used the notorious E. coli to compare their lipoprotein synthesis techniques.

By genetically removing the lipoprotein machinery in E. coli and replacing it with pieces of the Bacteriodes genome, they discovered that the latter used an entirely different enzyme, aptly dubbed lipoprotein N-acyltransferase in Bacteroides, also referred to as Lnb, to do the same thing. 

Their work was recently published in PNAS.

Additionally, they demonstrated that deleting Lnb interfered with cell growth and processing of carbohydrates, a fact that could be exploited in the development with new antibiotics. 

“While Bacteroides are considered good bacteria, they can act as pathogens outside of the gut,” said Koropatkin. 

“Discovering differences in physiology of this bacteria could provide us with something that can be specifically targeted to stop infection.”

Additional authors: Jiawen Jiang, Mariana G. Sartorio, Nichollas E. Scott, Jenna M. Peterson, Jonathan Z. Sexton and Mario F. Feldman.

Paper cited: “Identification and characterization of the lipoprotein N-acyltransferase in Bacteroides” PNAS. DOI: 10.1073/pnas.2410909121

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