Scientists Uncover the Slime Secret Behind Plant-Wilting Bacteria
A new study reveals the sticky reason why Ralstonia bacteria are such devastating plant killers. The research, published in the Proceedings of the National Academy of Sciences, is a unique collaboration between plant pathologists and engineers at the University of California, Davis. It uncovers the role of a slimy substance in the bacteria's ability to rapidly wilt tomato, potato, and various other crops.
Ralstonia solanacearum can lay dormant in damp soils for years before infecting plants, quickly spreading through the water-carrying vessels (xylem). Within days, infected plants wilt and die.
"It's like a heart attack for plants," explains Tiffany Lowe-Power, associate professor of plant pathology. "These bacteria clog the vessels, causing plants to wilt and die."
Ralstonia bacteria produce a slimy film, which is unusually sloppy and challenging to work with. This film is made of a long, sugar-like molecule called exo polysaccharide 1 (EPS-1).
"Ralstonia are incredibly unappealing," Lowe-Power notes. "There's a real sense of disgust."
The challenge was understanding how EPS-1 contributes to Ralstonia's plant-killing abilities. While microbiologists and geneticists have made progress, a deeper understanding required a physicist's perspective.
Enter Hari Manikantan, associate professor in the Department of Chemical Engineering. Manikantan studies complex multiphase fluids, including sticky substances like saliva and lung surfactants.
"I love goop of all forms," Manikantan says. "The question is what's the relevant time scale."
Manikantan and Lowe-Power's collaboration began during a new faculty training session before the pandemic. They used Manikantan's lab equipment to measure the viscoelastic properties of secretions collected from Ralstonia colonies. The key discovery? The goop from pathogenic Ralstonia flows easily under the shear forces found in plant xylem vessels, enabling rapid spread throughout infected plants.
The team further investigated this trait's prevalence. They tested other Ralstonia strains, including those without EPS-1, and collaborated with colleagues nationwide to analyze other bacteria related to Ralstonia wilt pathogens.
"This polysaccharide is unique to plant pathogens," confirms graduate student Matthew Cope-Arguello. "The research explains why EPS-1 makes these bacteria so pathogenic and provides an experimental system for engineers and soft matter physicists to study."
The study's implications are significant. Biologists gain insight into why EPS-1 enhances Ralstonia's pathogenicity. Engineers and physicists receive a valuable system for mathematical modeling. The collaboration between plant pathologists and engineers demonstrates the power of interdisciplinary research in addressing complex agricultural challenges.
