Publications

4479

ABSTRACT Bacterial endosymbionts of the pine bark adelgid, Pineus strobi (Insecta: Hemiptera: Adelgidae), were investigated using transmission electron microscopy, 16S and 23S rRNA-based phylogeny, and fluorescence in situ hybridization. Two morphologically different symbionts affiliated with the Gammaproteobacteria were present in distinct bacteriocytes. One of them (“ Candidatus Annandia pinicola”) is most closely related to an endosymbiont of Adelges tsugae , suggesting that they originate from a lineage already present in ancient adelgids before the hosts diversified into the two major clades, Adelges and Pineus . The other P. strobi symbiont (“ Candidatus Hartigia pinicola”) represents a novel symbiont lineage in members of the Adelgidae. Our findings lend further support for a complex evolutionary history of the association of adelgids with a phylogenetically diverse set of bacterial symbionts.

Huanglongbing (HLB) is a highly detrimental citrus disease associated with ‘Candidatus Liberibacter asiaticus’, a nonculturable alpha-proteobacterium. Characterization of the bacterial populations is important for development of disease management strategies. In this study, the ‘Ca. L. asiaticus’ populations in eight provinces in southern China where HLB is endemic were analyzed based on tandem repeat number (TRN) variations in a previously characterized genomic locus CLIBASIA_01645. Of the 224 HLB samples collected, 175 (78.3%) samples yielded single polymerase chain reaction (PCR) amplicons (the single amplicon group, SAG) and 49 (21.7%) samples produced multiple PCR amplicons (the multiple amplicon group, MAG). Variations in SAG are summarized by Nei's diversity index (H) and ratio of TRN ≤ 10/TRN > 10 genotypes (R10). Variations in the MAG are described by the percentage of occurrence (PMAG). At an orchard-level comparison, the ‘Ca. L. asiaticus’ population from a Guangdong orchard (n = 24) showed H = 0.50, R10 = 23, and PMAG = 0, significantly different from that of the non-Guangdong orchards in Yunnan (n = 23), H = 0.83, R10 = 2.3, and PMAG = 11.5, and in Hainan (n = 35), H = 0.88, R10 = 1.5, and PMAG = 16.7. In a region-level consideration, the Guangdong ‘Ca. L. asiaticus’ population (n = 78) was H = 0.77, R10 = 25, and PMAG = 1.3, whereas the non-Guangdong population (n = 84) was H = 0.91, R10 = 1.6, and PMAG = 26.9. Overall, significant differences were observed between the ‘Ca. L. asiaticus’ population from Guangdong Province and those from the other provinces. A strong aggregation of TRN = 6, 7, and 8 genotypes is characteristic to the ‘Ca. L. asiaticus’ population in Guangdong. Referenced to genome annotation, we propose that rearrangement of tandem repeats at locus CLIBASIA_01645 could be associated with bacterial environmental adaptation.