Washington State University researchers have for the first time grown the bacteria in a laboratory that causes Citrus Greening Disease, considered the world’s most harmful citrus disease.

Being able to grow the elusive and poorly understood bacterium, Candidatus Liberibacter asiaticus (CLas), will make it easier for researchers to find treatments for the disease that has destroyed millions of acres of orange, grapefruit and lemon groves around the world and has devastated the citrus industry in Florida.

WSU was selected three years ago for a USD2 million US Department of Agriculture grant to study the bacteria. The disease, formally known as Huánglóngbìng, (HLB), is spread by Asian citrus psyllids insects. It attacks the vascular system of citrus trees and causes fruit to become green, misshapen, and bitter-tasting.

A critical step in coming up with weapons to fight the disease is being able to study it in the lab, but the CLas bacterium is notoriously difficult to grow. With a small genome, CLas is thought to depend on very specific nutrient availability and possibly compounds secreted by other nearby bacteria.

Using infected citrus tissue as their starting point, the researchers developed a biofilm, a kind of bacterial city that allows a variety of bacteria to thrive. Instead of a rich growth medium that would crowd out the CLas, the researchers severely limited the growth of partner bacteria and created a medium with the specific nutrients, acidity, incubation temperatures, and oxygen levels that are optimal for CLas. The researchers were able to transfer the orange-coloured culture and grow new cultures in their biofilm reactors, which they have maintained for more than two years.

The team is now working to purify the culture, which will further help researchers to study it.  They are also developing genetic-based methods to understand and mitigate the spread of the disease. Phys.org