Bacterium Protects Plants from Disease in Attempt to Gain Dominance
Most natural environments harbor a stunningly diverse collection of microbial species. Within these communities, bacteria compete with their neighbors for space and resources.
Members of the rare biosphere that are amplified under favorable conditions to which they are pre-adapted can give rise to discrete, abundant populations. The potential pool of microbial competitors is therefore vast, and a wide range of mechanisms can be responsible for the emergence and radiation of dominant microbial populations. Nutritional resources are a focal point of microbial competition.
Now, in this regard, another warring bacterium has been found by the scientists at McMaster University. They have also been able to identify a toxin the soil-dwelling bacterium employs to get rid of its enemies which in turn has been found to offer protection to the plant against its pathogens.
The bacterium Pseudomonas protegens hold the ability to kill soil-dwelling plant pathogens, including fungi and bacteria that attack the roots of important crops such as cotton by the means of the toxic, T6SS injection.
“[The T6SS] is this molecular nanomachine that injects toxic protein into other species of bacteria and kills them,” lead researcher, John Whitney said. “Plant protective bacteria that have [T6SS] can protect plants from pathogens better relative to [bacteria] that don’t have it.
”Pseudomonas protegens releases diverse antimicrobial compounds into the soil, but the study focused specifically on those compounds that it was injecting directly into other bacteria through the type VI secretion system, or T6SS.
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.
Through the course of the study, the team found 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+. It 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.
Delving deeper, the team next analysed the genome of several other bacteria to determine 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 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.
