SAVE THE ZEST

Bacteria threaten to kill America’s $3-billion orange industry—so scientists are weaponizing viruses to fight it

Humans are a mere blip in the epic battle between bacteria and viruses. Long before we evolved, bacteria and viruses were at each other’s throats. And long after we are gone, they will still be at it.

Even in that blip, however, humans have a found way to change the story just that little bit. In one corner of the world, scientists are genetically engineering viruses to get rid of bacteria threatening the $3.3-billion orange industry in the US.

The culprit bacteria belongs to the genus Liberibacter, and it causes citrus trees to have bitter, misshaped fruits with green lower halves. Since its arrival in the US in 2005, it has spread very quickly, thanks to the flying insect called Asian citrus psyllids (Diaphorina citri). If it isn’t stopped, it could end production of citrus fruits in the US.

The savior could be citrus tristeza virus, which—without being engineered—is actually known to cause slow death of citrus trees. The engineered version, however, is benign to the fruit and goes after Liberibacter instead.

The idea of deploying engineered viruses comes courtesy of the Southern Garden Citrus, a producer of oranges in Florida. Field trials are underway, and now the company is seeking the approval of the US Food and Drug Administration (FDA) for commercial use. The approval process may take two years.

The period of public comment ended last week, and the FDA will now be assessing the environmental impact of the engineered virus. Because the virus doesn’t affect the fruit, Southern Garden Citrus can argue that the plants using it won’t produce genetically modified (GM) oranges. This way the company could sidestep regulations and public outcry usually attached to GM crops.

“There’s a real race on right now to try to save the citrus,” Carolyn Slupsky, a food scientist at the University of California at Davis, told Nature. “This disease is everywhere, and it’s horrible.”

The engineered virus isn’t the only weapon against Liberibacter. Scientists are also trying to genetically engineer the crop using a technique called CRISPR to create varieties that are resistant to the bacterial disease. Others are using another technique called RNA interference to disrupt the genes that allow the insects to spread the bacteria.


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