Characterization of the bacterial communities of psyllids associated with Rutaceae in Bhutan by high throughput sequencing

Morrow et al. BMC Microbiology (2020) 20:215 https://doi.org/10.1186/s12866-020-01895-4 RESEARCH ARTICLE Open Access Characterization of the bacterial communities of psyllids associated with Rutaceae in Bhutan by high throughput sequencing Jennifer L. Morrow1, Namgay Om2,3, George A. C. Beattie2, Grant A. Chambers4, Nerida J. Donovan4, Lia W. Liefting5, Markus Riegler1 and Paul Holford2* Abstract Background: Several plant-pathogenic bacteria are transmitted by insect vector species that often also act as hosts. In this interface, these bacteria encounter plant endophytic, insect endosymbiotic and other microbes. Here, we used high throughput sequencing to examine the bacterial communities of five different psyllids associated with citrus and related plants of Rutaceae in Bhutan: Diaphorina citri, Diaphorina communis, Cornopsylla rotundiconis, Cacopsylla heterogena and an unidentified Cacopsylla sp. Results: The microbiomes of the psyllids largely comprised their obligate P-endosymbiont ‘Candidatus Carsonella ruddii’, and one or two S-endosymbionts that are fixed and specific to each lineage. In addition, all contained Wolbachia strains; the Bhutanese accessions of D. citri were dominated by a Wolbachia strain first found in American isolates of D. citri, while D. communis accessions were dominated by the Wolbachia strain, wDi, first detected in D. citri from China. The S-endosymbionts from the five psyllids grouped with those from other psyllid taxa; all D. citri and D. communis individuals contained sequences matching ‘Candidatus Profftella armatura’ that has previously only been reported from other Diaphorina species, and the remaining psyllid species contained OTUs related to unclassified Enterobacteriaceae. The plant pathogenic ‘Candidatus Liberibacter asiaticus’ was found in D. citri but not in D. communis. Furthermore, an unidentified ‘Candidatus Liberibacter sp.’ occurred at low abundance in both Co. rotundiconis and the unidentified Cacopsylla sp. sampled from Zanthoxylum sp.; the status of this new liberibacter as a plant pathogen and its potential plant hosts are currently unknown. The bacterial communities of Co. rotundiconis also contained a range of OTUs with similarities to bacteria previously found in samples taken from various environmental sources. (Continued on next page) * Correspondence: 2 Western Sydney University, School of Science, LB 1797, Penrith, NSW 2752, Australia Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Morrow et al. BMC Microbiology (2020) 20:215 Page 2 of 16 (Continued from previous page) Conclusions: The bacterial microbiota detected in these Bhutanese psyllids support the trends that have been seen in previous studies: psyllids have microbiomes largely comprising their obligate P-endosymbiont and one or two Sendosymbionts. In addition, the association with plant pathogens has been demonstrated, with the detection of liberibacters in a known host, D. citri, and identification of a putative new species of liberibacter in Co. rotundiconis and Cacopsylla sp. Keywords: Endosymbiont, Microbiome, Psyllid, ‘Ca. Liberibacter’, Wolbachia Background Within the Psylloidae, three of the families proposed by Percy et al. [1], the Liviidae, Psyllidae and Triozidae, contain vectors of plant pathogenic bacteria. Vectors of liberibacters (Alphaproteobacteria) include species of Arytainilla, Bactericera, Cacospylla, Diaphorina and Trioza [[2] and references within]. Species of Cacopsylla transmit a range of phytoplasmas [3–8], and Bactericera trigonica Hodkinson vectors a phytoplasma to carrots [9]. Sometimes, individual psyllid species are able to vector a range of pathogens. Both Trioza erytreae Del Guercio (Triozidae) and Diaphorina citri Kuwayama (Liviidae) can transmit ‘Ca. Liberibacter asiaticus’ (hereafter CLas) and ‘Ca. L. africanus’ [10–12] and D. citri is also a vector for ‘Ca. L. americanus’ [13] and ‘Ca. Phytoplasma aurantifolia’ causing witches’ broom disease of lime [14]. These phytoplasmas and liberibacters are members of lineages that are ecologically specialized. Within their plant hosts, they are intracellular and restricted to the phloem, and within their insect hosts and vectors, they colonize various tissues and persist throughout the insects’ lifespan; hence, the insects are considered as alternative hosts rather than passive carriers [15, 16]. In addition to these two lineages, the bacterium, Erwinia amylovora (Burrill) Winslow et al. (Enterobacteriaceae), the causal agent of fireblight, has been found to be transmitted by Cacosylla pyricola (Förster) [17, 18] and, in South America, Russelliana solanicola Tuthill (Psyllidae) has been identified as the first known psyllid vector of a plant virus, the potato rugose stunting virus [19]. In addition to vectoring plant pathogens, psyllids, like other insects, harbour a diverse array of other bacteria [20] whose association with their host varies on a continuum from obligate to facultative [21]. The nitrogen content of phloem on which psyllids feed is low [22] particularly in concentrations of essential amino acids [23, 24]. To overcome these deficiencies, some insects have developed obligate associations with endosymbiotic bacteria (primary endosymbionts (P-endosymbionts)) [25] thereby allowing them to utilise nutrient-poor environments such as xylem and phloem [26, 27]. In psyllids, the P-endosymbiont is ‘Ca. Carsonella ruddii’ (hereafter Carsonella; Gammaproteobacteria) that is housed within specialised host cells called bacteriocytes that aggregate into bacteriomes [28–30]. These P-endosymbionts are vertically transmitted resulting in strict co-speciation with their psyllid hosts within families, genera and species [28–30]. The resulting clonality has induced a drastic reduction in genome size, through loss of up to 90% of ancestral genes including, in some cases, the loss of s (...truncated)