Citrus destructive bacterial relative may also be infectious

A bacterial species closely related to the deadly citrus green disease is rapidly evolving in its ability to infect host insects, and possibly plants as well.

The newly identified species belongs to Liberibacter, a family of bacteria known to infect several economically important crops. There are nine known species of Liberibacter, including one that infects potatoes and three that are associated with citrus greening.

Citrus greening, also known as Huanglongbing, is the number one citrus killer in the world. Although many are working on options, there are currently no effective prevention or treatment options on the market.

Given the destructive qualities of his mom and dad, the UC Riverside scientists set out to understand how the new species, L. capsica, genetically resembles other kinds of Liberibacter. -19, bacteria become variants of concern if their mutations may have an impact on pathogenic or transmissible properties,” said Allison Hansen, UCR entomologist and head of the study.

Many Liberibacters share genes that allow them to live inside a host.

“These bacteria acquire DNA from their hosts, so without a host they are functional, they will die,” Hansen said.

For this study, the research team identified relied 21 genes in L. capsica that rapidly evolve into amino acid mutations associated with infectious qualities. This development is documented in a new posting in the journal Microbiology Spectrum.

A subset of mutations that the team repeatedly found relate to genes affecting pilus, from tiny bacterial “hairs” that allow bacteria to move within host insects and take up DNA. The insects then transmit the bacterium to the plants.

L. capsica was found by chance in a few flying insects on a pepper plant in Brazil. These insects, the psyllids, are known pests of pepper. However, it is not yet known whether L. capsica infects peppers or other crops.

It may be difficult to gather direct evidence to know whether the bacterium infects pepper tissue, as Hansen’s team only had one sample and L. capsica cannot be cultured in the lab.

The psyllids were collected at Brazil by Diana Percy, an entomologist at the University of British Columbia and a frequent collaborator with Hansen. Percy travels the world in search of psyllids but didn’t know they would harbor new bacteria. This discovery was later made in Hansen’s lab after Percy shared the psyllids she had obtained overseas.

“We inform scientists in Brazil and other places to select the plants,” Hansen said. “This should be on everyone’s radar for epidemic potential given Liberibacter’s propensity to be serious plant pathogen brokers on domesticated crops.”

Integral to this study was the work of Ariana Sanchez, an undergraduate microbiology student at UCR, who focused on insect-borne bacterial pathogens. Sanchez is the Department of Entomology’s Lead Inclusion Researcher.

The Department established the Advancing Inclusivity in Entomology Fellowship in response to the Black Lives Make any difference movement and the death of George Floyd in 2020. The faculty recognized the need to support students from marginalized groups who have a passion for studying insects but who face systemic barriers that exclude them from research. Opportunities.

By helping to identify the evolutionary pathways of L. capsica, Sanchez made an important contribution to the knowledge of Liberibacter.

“Being able to understand pathogens like these and how they interact with the insects that carry them is so critical to the security of our food supply,” Hansen said.

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