By Scott Weybright, College of Agricultural, Human & Natural Resource Sciences

Citrus-greening-detailPULLMAN, Wash. – Three Washington State University researchers have received a $2.1 million grant to help save the U.S. and global citrus industry. They will develop methods of growing a citrus-destroying bacteria so that strategies to fight the disease it causes can be pursued.

Huánglóngbìng, or HLB, is also called “citrus greening disease,” and it is destroying orange, grapefruit and lemon trees around the world. Scientists haven’t been able to grow and maintain cultures of the bacterium that causes the disease.

“The simple answers didn’t work and we need a way to fight this,” said biochemist David Gang, a fellow in WSU’s Insitute of Biological Chemistry.

“This disease is wiping out the citrus industry in the U.S., and in five years there may not be any citrus orchards left,” he said. “I like orange juice too much to let it go away without a fight.”

Safe location, combined expertise

The grant is part of the U.S. Department of Agriculture’s Specialty Crop Research Initiative Citrus Disease Research and Extension Program. Gang’s WSU colleagues are Haluk Beyenal in chemical engineering and Anders Omsland in the Paul G. Allen School for Global Animal Health. Also on the project are Nabil Killiny-Mansour and Stephen Futch, from the Citrus Research and Education Center at the University of Florida, and Judith Brown, from the University of Arizona.

Citrus-drop-web
Citrus trees infected with HLB drop much of their fruit before it matures and can be harvested.

WSU was selected in part because citrus isn’t grown in Washington, so there is no chance of accidentally infecting a crop. More important, Gang said, WSU has the right combination of expertise to tackle the problem in a new way.

HLB is thought to spread from tree to tree via tiny insects called psyllids. The bacterium survives and multiplies in psyllids and in trees; but in a lab setting, it just sits there and eventually dies.

Gang said the HLB bacterium is missing something in its metabolism that doesn’t allow it to grow in a lab environment. He wants to find that missing metabolic component.

Each WSU expert brings a different perspective on how to culture this serious pathogen: “It’s really a combination of all our efforts and working together to see if we can get the bacterium to grow,” Gang said.

Long on talent, short on time

Beyenal is an expert in biofilm culturing. The HLB bacterium is thought to grow within trees and psyllids inside of biofilms, or groups of cells in organisms that protect themselves by secreting protective or slightly slimy compounds. Culturing anything from a biofilm is traditionally difficult, Gang said, but Beyenal has developed an effective method for getting around that.

Citrus-greening-web
Citrus fruits like oranges infected with HLB stay green looking and are much smaller than normal fruit.

With expertise in the metabolic capacity of parasitic bacteria, Omsland will characterize the metabolic potential of the bacterium as a means to design a culture medium. He will use a cell culture system that can be infected with the bacterium to generate purified bacteria for analysis, Gang said.

The USDA grant runs for two years, although Gang said it normally takes four to five years for this type of work. But given the speed at which HLB is destroying citrus trees, that timeline won’t work.

“We have two years to show the USDA we’re making progress,” Gang said. “We want to figure this out quickly and help out this vital industry.”

 

Contacts:
David R. Gang, WSU Institute of Biological Chemistry, 509-335-0550, gangd@wsu.edu
Haluk Beyenal, WSU School of Chemical Engineering and Bioengineering, 509-335-6515, beyenal@wsu.edu
Anders Omsland, WSU Paul G. Allen School for Global Animal Health, 509-335-3916, omslanda@vetmed.wsu.edu