JBC: New insights into the molecular weapons of the plant microbiome
Like all organisms, plants are associated with bacterial communities in which helpful and harmful bacteria compete for dominance. Among the weapons of these warring bacteria are molecular syringes that some bacteria can use to inject toxins into others. In a study published in the Journal of Biological Chemistry, researchers at McMaster University in Canada pinpointed the identity of one such toxin used by a soil-dwelling bacterium that protects plants from disease.
The NAD-degrading enzyme Tne2 is secreted through the type VI secretion system of the plant-protective bacterium Pseudomonas protegens.Courtesy of John Whitney/McMaster University
The bacterium Pseudomonas protegens can kill soil-dwelling plant pathogens, including fungi and bacteria, that attack the roots of important crops such as cotton. P. protegens releases diverse antimicrobial compounds into the soil, but John Whitney was curious specifically about the compounds that it was injecting directly into other bacteria through the type VI secretion system, or T6SS.
The T6SS “is this molecular nanomachine that injects toxic protein into other species of bacteria and kills them,” Whitney said. “Plant protective bacteria that have (T6SS) can protect plants from pathogens better relative to (bacteria) that don’t have it.”
Jenny Tang and Nathan Bullen, undergraduate students from the University of Waterloo working with Whitney on a co-op work-study assignment, spearheaded the discovery that the toxic protein used by P. protegens against other bacteria acts on a molecule found in nearly all living cells: nicotinamide adenine dinucleotide, or NAD+.
NAD+ is a cofactor, or “helper” molecule, in many biochemical reactions. By injecting a protein that destroys NAD+, P. protegens is able to kill other bacteria.
The team then investigated the genome sequences of hundreds of other bacteria to see how widespread the strategy of targeting NAD+ is in microbial warfare. They found that many bacteria with secretion systems carry genes similar to the one encoding the NAD-targeting toxin.
“We started to see that this isn’t just a way of killing that is enacted by plant-protective bacteria,” Whitney said. “If you look at the distribution of this (protein) among all sequenced bacteria, it appears that many different bacteria in many different environmental niches use this mode of action to outcompete other bacteria.”
The abundance of these toxins in nature raises questions: How do different bacteria in different environments evolve to resist this toxin? Are NAD-targeting toxins more effective against some bacterial species than others? Understanding the diversity of bacterial weapons is an active area of study among agricultural researchers who would like to develop better ways to fight plant diseases.
“The identification and characterization of antibacterial toxins produced by plant-protective bacteria may one day allow us to engineer these bacteria to have enhanced ability to suppress pathogens,” Whitney said.
Enjoy reading ASBMB Today?
Become a member to receive the print edition four times a year and the digital edition weekly.
Learn moreGet the latest from ASBMB Today
Enter your email address, and we’ll send you a weekly email with recent articles, interviews and more.
Latest in Science
Science highlights or most popular articles
Transforming learning through innovation and collaboration
Neena Grover will receive the William C. Rose Award for Exemplary Contributions to Education at the 2025 ASBMB Annual Meeting, April 12–15 in Chicago.
Guiding grocery carts to shape healthy habits
Robert “Nate” Helsley will receive the Walter A. Shaw Young Investigator in Lipid Research Award at the 2025 ASBMB Annual Meeting, April 12–15 in Chicago.
Quantifying how proteins in microbe and host interact
“To develop better vaccines, we need new methods and a better understanding of the antibody responses that develop in immune individuals,” author Johan Malmström said.
Leading the charge for gender equity
Nicole Woitowich will receive the ASBMB Emerging Leadership Award at the 2025 ASBMB Annual meeting, April 12–15 in Chicago.
CRISPR gene editing: Moving closer to home
With the first medical therapy approved, there’s a lot going on in the genome editing field, including the discovery of CRISPR-like DNA-snippers called Fanzors in an odd menagerie of eukaryotic critters.
Finding a missing piece for neurodegenerative disease research
Ursula Jakob and a team at the University of Michigan have found that the molecule polyphosphate could be what scientists call the “mystery density” inside fibrils associated with Alzheimer’s, Parkinson’s and related conditions.