Distribution and variation of bacterial endosymbiont and “candidatus liberibacter asiaticus” titer in the huanglongbing insect vector, diaphorina citri kuwayama

Authors: HOSSEINZADEH, SAEED - Cornell University; SHAMS-BAKHSH, MASOUD - Tarbiat Modares University; MANN, MARINA - Cornell University; FATTAH-HOSSEINI, SOMAYEH - Boyce Thompson Institute; BAGHERI, ABDOOLNABI - Agricultural Research, Education And Extension Organization (AREEO); Heck, Michelle

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2018
Publication Date: 11/24/2018
Citation: Hosseinzadeh, S., Shams-Bakhsh, M., Mann, M., Fattah-Hosseini, S., Bagheri, A., Heck, M.L. 2018. Distribution and variation of bacterial endosymbiont and “candidatus liberibacter asiaticus” titer in the huanglongbing insect vector, diaphorina citri kuwayama. Microbial Ecology. 78(1):206-222. https://doi.org/10.1007/s00248-018-1290-1.
DOI: https://doi.org/10.1007/s00248-018-1290-1

Interpretive Summary: Citrus greening, also called Huanglongbing (HLB) is the most destructive and difficult to control citrus disease. All citrus cultivars are susceptible to HLB, and no resistant citrus species have been found to date. “Candidatus Liberibacter asiaticus” (CLas) is a phloem-limited, gram-negative, fastidious bacterium associated with citrus greening disease. The Asian citrus psyllid is an economic insect pest of citrus. The insect is the vector that is responsible for spreading the CLas bacterium among citrus trees. Discovering novel and effective HLB management strategies is urgent and requires an improved understanding of CLas pathogenicity and interactions between the bacterium and its insect vector. The insect vector also has beneficial bacteria that are critical to the insect’s survival. Very little is known about how these beneficial bacteria in the insect interact with CLas. Here we show strong relationships among the relative abundances beneficial bacteria in the insect and CLas in all psyllid tissues where they infect, strongly suggesting direct inter-species interactions.

Technical Abstract: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is an economic insect pest in most citrus-growing regions and the vector of “Candidatus Liberibacter asiaticus” (CLas), one of at least three known bacteria associated with Huanglongbing, (HLB, or citrus greening disease). D. citri harbors bacterial endosymbionts including Wolbachia pipientis (strain Wolbachia wDi) ‘Candidatus Carsonella ruddii,’ and ‘Candidatus Profftella armatura.’ Many important functions of these bacteria can be inferred from their genome sequences, but their interactions with each other, CLas and their D. citri host is poorly understood. In the present study, the titers of the endosymbionts in different tissues, in each sex, and in insects reared on healthy citrus (referred to as unexposed) and CLas-infected citrus (referred to as CLas-exposed) D. citri were investigated using real-time, quantitative PCR (qPCR) using two different quantitative approaches. Wolbachia and CLas were detected in all insect tissues. The titer of Wolbachia was higher in heads of CLas-exposed males as compared to unexposed males. In males and females, Wolbachia titer was highest in the Malpighian tubules. The highest titer of CLas was observed in the gut. Profftella and Carsonella titers were significantly reduced in the bacteriome of CLas-exposed males compared with to unexposed males, but this effect was not observed in females. In ovaries of CLas-exposed females, the Profftella and Carsonella titers were increased as compared to non-exposed females. CLas appeared to influence the overall levels of the symbionts but did not drastically perturb the overall microbial community structure. In the all assessed tissues, CLas titer in males was significantly higher than that of females using absolute quantification. These data provide a better understanding of multi-trophic interactions regulating symbiont dynamics in the HLB pathosystem