PARIS (AFP) - The discovery of a new mechanism by which a known bacterium infects numerous plants could one day help uncover a new class of anti-cancer drugs for humans, according to a study.

Researchers looking at the single-cell animal that causes brown spot disease in common green beans isolated a molecule, called syringolin A, that boosts the bacterium’s virulence and accounts for its ability to infect.

A genetically-modified form of the bacterium — Pseudomonas syringae pv. syringae (Pss) — in which the molecule was removed lost the capacity to attack the plants, confirming the pathogen’s powers.

But what surprised lead scientist Robert Dudler of the Munich Technical University and his colleagues was how the offending molecule worked.

Syringolin A, they found, enters plant host cells and prevents a protein structure called proteasome — which plays a critical role in breaking down other, undesirably proteins — from doing its job.

“To activate the plant defence response mechanism you need the proteasome,” Dudler told AFP. “Syringolin A seems to be a natural form of proteasome inhibitor.”

What has been a blight for vegetable farmers, however, could be a big bang in medicine.

“The discovery of a novel family of inhibitory natural products, which we refer to as sybractins, may also have implications for the development of anti-cancer drugs,” he said.

Previous research has shown that Syringolin A has the capacity to shrink certain cancers, opening the possibility that this and similar molecules might be developed as new cancer therapies.

The equivalent of Syringolin A is found in other pathogenic bacteria, notably one which causes melioidosis, or Whitmore’s disease, in humans.

This holds the promise, says Dudler, that these organisms are capable of manufacturing proteasome inhibitors in the same sybractin class.

The pathogen responsible for Whitmore’s disease, Burkholderia pseudomallei, has been considered as a potential agent for biological warfare and biological terrorism, according to the US Centers for Disease Control and Prevention in Atlanta, Georgia.

Pss is an important model in molecular plant pathology. Its complete genome was sequenced in 2005 in the United States.

The discovery of a new mechanism by which a known bacterium infects numerous plants could one day help uncover a new class of anti-cancer drugs for humans, according to a study. Researchers looking at the single-cell animal that causes brown spot disease in common green beans isolated a molecule, called syringolin A, that boosts the bacterium’s virulence.

Pseudomonas syringae is a rod shaped, Gram-negative bacterium with polar flagella. It is a member of the Pseudomonas genus, and based on 16S rRNA analysis, P. syringae has been placed in the P. syringae group. It is a plant pathogen which can infect a wide range of plant species, and exists as over 50 different pathovars. Many of these pathovars were once considered to be individual species within the Pseudomonas genus, but molecular biology techniques such as DNA hybridization have shown these to in fact all be part of the P. syringae species. It is named after the lilac tree (Syringa vulgaris), from which it was first isolated.

P. syringae tests negative for arginine dihydrolase and oxidase activity, and forms the polymer levan on sucrose nutrient agar. It is known to secrete the lipodepsinonapeptide plant toxin syringomycin, and it owes its yellow fluorescent appearance when cultured in vitro on King’s B medium to production of the siderophore pyoverdin.

Since the 1970’s, P. syringae has been implicated as an atmospheric ‘biological ice nucleator’. Recent evidence has suggested that the species plays a larger role than previously thought in making it rain and snow.

Sources: Wikipedia, UK News Yahoo

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