Abstract
The relationship between the causal agent of Huanglongbing (HLB), Ca. Liberibacter asiaticus(Las), and the naturally occurring endosymbiotic community of its insect vector, the Asian citrus psyllid (ACP), Diaphorina citri, was studied. Variation was observed in the titer of Las within an ACP population feeding on the same material. The cause of this disparity is unknown, and has implications for Las transmission and the spread of HLB. This study utilizes culture independent methods to establish the relationship between the ACP’s microbial community and Las acquisition. DNA from 21 psyllids was amplified using universal 16S rRNA primers with Illumina adaptor regions and a sample-specific 7- base identifier. These amplicons were then batch-sequenced on the Illumina platform. The resulting sequences were separated by the identifier, and compared to known sequences in a 16S rRNA database. The microbial communities of each psyllid were compared to determine whether a correlation exists between the ACP’s endosymbionts and level of Las acquisition.ACPs were dominated by the same four bacterialgenera regardless of the abundance of Ca.Liberibacter. A combination of qPCR and Illumina sequencing was used to establish an infection gradient among the sampled ACPs. The Ca. Liberibacter titer within the insect was found to have a strong negative relationship with an endosymbiont residing in the syncytium of the mycetocyte and a positive relationship with Wolbachia. These correlations have implications in the acquisition of Las by the ACP as well as the activities of Las within this vector.
Highlights
Huanglongbing (HLB), or citrus greening, is killing mature trees and decreasing the quality of fruit to unmarketable levels [1, 2]
Liberibacter asiaticus (Las) is the likely cause of HLB in Asia and the Americas where it is vectored by a Sternorrhynchian insect, the Asian citrus psyllid (ACP) Diaphorina citri [1,3,4]
These multiplexed 16S rRNA amplicon sequencing methods allow for the simultaneous characterization of 1435 microbial communities in a single Illumina sequencing run, with the generation of 12Mb of data for each sample
Summary
Huanglongbing (HLB), or citrus greening, is killing mature trees and decreasing the quality of fruit to unmarketable levels [1, 2]. Ca. Liberibacter asiaticus (Las) is the likely cause of HLB in Asia and the Americas where it is vectored by a Sternorrhynchian insect, the Asian citrus psyllid (ACP) Diaphorina citri [1,3,4]. Sternorrhyncha, formerly known as Homoptera, are a well-studied suborder of Hemioptera and include: plant hoppers, scale insects, aphids and psyllids. They are all sapfeeders and have cultivated close relationships with bacteria that synthesize essential nutrients absent in their diet. These primary symbionts are often housed in the insect’s bacteriocyte.
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