Journal News

JBC: New insights into the molecular weapons of the plant microbiome

Sasha Mushegian
Sept. 1, 2018

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 more
Sasha Mushegian

Sasha Mushegian is a postdoctoral fellow at Georgetown University. Follow her on Twitter.

Get 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

Gene-mutation pathway discovery paves way for targeted blood cancers therapies
News

Gene-mutation pathway discovery paves way for targeted blood cancers therapies

Nov. 3, 2024

A new study by researchers at the universities of Texas and Chicago explains the enzymatic activity that’s needed for tumor suppression in leukemias and other cancers.

Candy binges can overload your gut microbiome
News

Candy binges can overload your gut microbiome

Nov. 2, 2024

While most Halloween candies contain lots of sugar, some are better for your gut microbiome than others.

Water rescues the enzyme
Essay

Water rescues the enzyme

Oct. 31, 2024

“Sometimes you must bend the rules to get what you want.” In the case of using water in the purification of calpain-2, it was worth the risk.

Virtual issue celebrates water in ASBMB journals
Journal News

Virtual issue celebrates water in ASBMB journals

Oct. 30, 2024

Read a dozen gold open-access articles covering exciting research about the society’s 2024 Molecule of the year.

There are worse things in the water than E. coli
News

There are worse things in the water than E. coli

Oct. 29, 2024

E. coli levels determined whether Olympic swimmers could dive into the Seine this past summer. But are these bacteria the best proxy for water contamination?

Biobots arise from the cells of dead organisms
News

Biobots arise from the cells of dead organisms

Oct. 27, 2024

Given the right conditions, certain types of cells are able to self-assemble into new lifeforms after the organism they were once part of has died.