Publications

4721

‘Candidatus Liberibacter asiaticus’ (CLas), the causal agent of citrus huanglongbing, is transmitted by the Asian citrus psyllid Diaphorina citri. While CLas-positive (CLas+) females exhibit increased fecundity and metabolic demands, their neuroendocrine regulation mechanisms remain unclear. We propose CLas manipulates dopamine (DA) signaling to enhance psyllid fecundity and CLas proliferation. Metabolomics revealed elevated DA in CLas+ females. Silencing DA synthesis genes and receptor DcDop2 via RNAi reduced lipid reserves, fecundity, and ovarian CLas titers. Through combined in vivo and in vitro experiments, we demonstrated that the microRNA miR-31a suppresses DcDop2 expression by binding to its 3’ untranslated region. Overexpression of miR-31a resulted in decreased DcDop2 expression and CLas titers in the ovaries, eliciting phenotypic defects akin to DcDop2 knockdown. Furthermore, DcDop2 knockdown and miR-31a overexpression reduced juvenile hormone (JH) levels and adipokinetic hormone (AKH) signaling in fat bodies and ovaries. Consequently, CLas regulates the DA-DcDop2 signaling axis to improve D. citri lipid metabolism and fecundity, while simultaneously promoting its replication. These findings reveal a coevolution between CLas proliferation and ovarian development in the insect host. This discovery enhances our understanding of the molecular interplay between plant pathogens and vector insects and offers novel targets and strategies for HLB field management.

Abstract Bacterial symbionts were shown to have significant beneficial impacts on the fitness of their host in insects, but little is known on the symbionts of spiders and their interactions with their hosts. Here, we assembled and investigated the circular 575 kb genome of Candidatus Argioplasma dusa, a novel bacterial symbiont of the wasp spider Argiope bruennichi . Phylogenomic analysis placed this species within the phylum Tenericutes, in a poorly characterized clade that may represent a new order-level lineage or affiliate with the Mycoplasmatales order. With 559 predicted genes, the genome is relatively small compared to other Tenericutes genomes (on average 969 genes) and has a low GC content of ~24%. While the genome encodes genes for proteins involved in glycolysis and fermentative acetate production, it revealed minimal biosynthetic capabilities with pathways for nucleotide, amino acid and vitamin biosynthesis being absent in Ca . Argioplasma dusa. This suggests an intracellular endosymbiotic lifestyle within the spider host. The symbiont was detected in A. bruennichi populations across the distribution range of the spider but appears to be absent in certain populations.

In 2024, an infestation of corn leafhoppers, Dalbulus maidis (DeLong) (Hemiptera: Cicadellidae), was detected in several commercial corn fields across Oklahoma (OK) (Faris et al. 2024). Corn hybrids in the infested field showed symptoms resembling maize bushy stunt, including chlorotic striping, reddening of leaves, production of multiple ears, and stunting. Visual disease incidence ranged from 25% to 100% among affected fields. Leaf samples from symptomatic plants were collected from 15 commercial corn fields across seven counties in OK (Payne, Logan, Caddo, Kay, Texas, Pottawatomie, and Grady) during September, October, and November of 2024. Each sample consisted of 3-4 symptomatic corn leaves randomly collected in each field. In addition, 43 corn leafhopper samples were collected from the symptomatic fields using handheld vacuums. Each corn leafhopper sample consisted of a minimum of 10 corn leafhoppers per field. In the laboratory, the corn leafhoppers were identified as D. maidis based on morphological characteristics as described (Faris et al. 2024). DNA from the 15 leaf samples was extracted from the leaf midrib and blade tissues using the DNeasy® Plant Mini Kit. Insect DNA was extracted using a CTAB-based method (Gorayeb et al. 2023), with each sample consisting of five pooled insects per field. DNA samples from plants and insects were initially screened using the R16F2n/R16R2 primer pair (Gundersen and Lee, 1996) for the presence of phytoplasmas. Seventeen insect and five plant samples tested positive for phytoplasma. Subsequent phytoplasma screening was performed on insect and plant samples collected from the same fields on the same dates, comprising a total of four insect and five plant samples. To further characterize the phytoplasma, a semi-nested PCR targeting the 16S rRNA gene was performed on these samples (four insect and five plant samples) using primer pairs P1/16S-SR followed by P1A/16S-SR (Wei et al. 2021), yielding an expected amplicon of approximately 1.5 Kb. An additional gene marker, the ribosomal protein (rp) gene, was also amplified using universal primers rpF1/rpR1 (Lee et al. 1998), producing 1.2 Kb PCR amplicons. PCR products were subjected to Sanger sequencing, and 16S rRNA and rp gene sequences were deposited in GenBank under accession numbers PX927497–PX927505 and PX993703-PX993711, respectively. BLASTn analysis of the 16S rRNA sequences showed 99.14–99.93% nucleotide identity with reference strains of ‘Candidatus Phytoplasma asteris’ associated with maize bushy stunt (accessions MW578284 and CP015149). Similarly, the rp gene sequences shared 99.91–100% nucleotide identity with the same reference strains. Using the iPhyClassifier tool (Zhao et al. 2013), the 16S rRNA gene sequences were classified within 16Sr group I, subgroup B, with a similarity coefficient of 1.0 (AP006628). The pairwise comparison and subsequent phylogenetic analysis showed that the OK isolates clustered within the 16SrI-B clade. This finding represents the first report of a 16SrI-B phytoplasma (‘Candidatus Phytoplasma asteris’) associated with maize bushy stunt in OK. Although currently classified as ‘Candidatus Phytoplasma asteris’, a proposal to establish a novel phytoplasma species, ‘Candidatus Phytoplasma zeae’, has been made based on ecological distinctiveness, vector specificity, whole-genome comparisons, and community consensus (Pellegrinetti et al. 2025).

Abstract De novo assembly of ancient and modern bacterial metagenomes can shed light on evolution and ecology of bacterial species that are challenging to culture. Tannerella and Porphyromonas are bacterial genera linked to periodontal disease, and understanding their evolution may reveal insights into their role in oral disease development. We performed pangenomic and phylogenetic analyses on a global set of isolates and metagenome-assembled genomes of the genera Tannerella (n = 238) and Porphyromonas (n = 976), including 66 genomes from ancient dental calculus samples (up to 14,800 years old), and modern oral samples from present-day living populations. We identify a novel species of oral Tannerella in modern and ancient humans, which we call Ca. Tannerella abscondita, that is related to and often mistaken for Tannerella forsythia but differs in its virulence repertoire. We reveal distinct niche tropism in Tannerella species and Porphyromonas pasteri, but not Porphyromonas gingivalis. There is limited phylogeographic structuring, and virulence genes are homogeneously distributed across continents and oral niches. Saliva-derived strains of T. forsythia and P. gingivalis from Oceania and T. serpentiformis and P. pasteri from Asia show enrichment of pseudogenes related to ecological niche transitions. A phylogenetic analysis of the P. gingivalis major fimbrial protein gene fimA reveals the genes cluster by genotypes, and that no ancient genes are found in genotypes I and Ib. Using de novo assembly for bacterial pangenomics improves the representation of oral genera found in reference databases and enhances our ability to study the evolutionary history of these taxa.

Insecticide applications are commonly recommended for managing Diaphorina citri, the vector of huanglongbing (HLB), but their effectiveness in reducing transmission of ‘Candidatus Liberibacter asiaticus’ (CLas), especially during continuous psyllid influx and shoot growth, remains unclear. This study evaluated the efficacy of foliar application of thiamethoxam and spinetoram in reducing CLas transmission in sweet orange seedlings. Two experiments were conducted up to 13 days after first spray. In experiment 1, CLas-positive psyllids were confined in seedlings every 2 days. Treatments were: control; S14, one spray at day 0; and S7, sprays at days 0 and 7. In experiment 2, psyllids were released for free choice within a screenhouse every 2 days. Treatments were: control, S14, S7, and S3, sprays at day 0 and every 3 days. Sprays on day 0 were over unfolded leaves (V2 stage). Psyllid mortality was assessed in experiment 1. Psyllid occupancy (percentage of seedlings with at least one psyllid) and abundance (number of psyllids per seedling) were assessed in experiment 2. After 6 months, seedlings were tested for CLas by qPCR. In experiment 1, cumulative psyllid mortality was higher in sprayed treatments than in the control for both insecticides, but HLB incidence was similar. In experiment 2, both psyllid occupancy and abundance decreased with shorter spray intervals, with the lowest HLB incidence in S3. These findings suggest that reducing spray intervals can limit CLas transmission during periods of shoot growth and continuous vector pressure. However, CLas transmission was not entirely prevented, highlighting the need for integrated, area-wide management strategies.

Candidatus Saccharibacteria (TM7) is an underexplored bacterial group within the human oral microbiome. These ultra-small, host-dependent organisms, despite their reduced genomes, significantly influence microbial balance and host immunity, exhibiting dual roles in oral health and disease and emerging as a key focus in microbiome research. This systematic review aimed to synthesize evidence on the prevalence, host interactions, genomic features, and ecological roles of TM7 in the oral cavity. A total of 13 peer-reviewed studies published between 2020 and 2025 were selected for detailed review based on predefined inclusion criteria, including clinical, laboratory, and metagenomic analyses focusing on TM7 detection, isolation, host specificity, and interactions with oral microbial communities. TM7 was found to be predominantly oral-adapted, exhibiting site-specific colonization with higher abundance in saliva. Coculture experiments demonstrated strict host dependence, particularly on Actinomyces, Schaalia, and Arachnia species, with strain-specific variations affecting host viability and microbial networks. TM7 genomes are highly reduced, with specialized adaptations including type IV pili and arginine deiminase pathways. Interactions with the immune system were context-dependent, with both immunomodulatory and pro-inflammatory outcomes observed. Detection methods significantly influenced TM7 prevalence and functional interpretation. Overall, TM7 represents a host-dependent, ecologically influential oral bacterium with genomic specialization, strain-level variability, and complex interactions within microbial communities. These findings highlight its potential roles in oral health and disease and emphasize the need for advanced multi-modal analytical approaches.

Abstract The pear psyllid Cacopsylla pyri is the main vector of ‘ Candidatus Phytoplasma pyri’, the causal agent of pear decline, a disease associated with severe yield losses in pear production. Phytoplasmas are further known to interfere with their vectors metabolism; therefore, we investigated whether an infection with ‘ Ca. P. pyri’ is associated with changes in nutrient storage of the pear psyllids. Additionally, we measured whether the phytoplasma infection is associated with differences in flight performance in C. pyri , as the flight activity of the vector is a key component of phytopathogen spread. Using a flight mill, we quantified flight distance, duration, and speed, and combined qPCR-based infection detection with colorimetric assays to determine protein, carbohydrate, and lipid content from the same individual. Infected psyllids contained significantly higher levels of soluble carbohydrates than uninfected individuals. Lipid content was not affected by the phytoplasma infections but was found to be consistently higher in males than in females, while protein levels did not vary with sex or infection status. Despite infection-related differences in carbohydrate levels, phytoplasma infection did not significantly affect flight duration, distance, or speed. These results indicate that infection-associated shifts in bulk carbohydrate storage do not translate into altered flight motivation or performance, suggesting a functional decoupling between metabolic state and realised dispersal capacity under standardised laboratory conditions.

Candidatus Liberibacter solanacearum (CLso), a pathogen of concern to the potato industry, which causes zebrachip disease, is vectored by the tomato/potato psyllid [ Bactericera cockerelli (Šulc)]. This study investigated whether Lycium ferocissimum acts as an overwintering green bridge enabling pathogen survival, while potatoes are absent. The potential of L. ferocissimum to act as a green bridge for other pathogens was also investigated. African boxthorn leaf samples were taken in Feb, Mar, and Apr 2023 in Canterbury, New Zealand, and endophytes were isolated and cultured. DNA was extracted from these pure-cultured endophytes as well as from leaves. Molecular methods were used to identify the cultured endophytes and to determine the presence of CLso. This study found several potentially pathogenic endophytes including Alternaria porri, Stemphylium eturmiunum , Stemphylium vesicarium, Pseudomonas spp., Erwinia spp. , Pantoea sp. , and Candidatus Liberibacter solanacearum. The percentage of leaves which tested positive for CLso increased from 2% in Feb 2023 to 39% in Apr 2023. CLso was found in leaves without evidence of psyllid feeding, which may indicate systemic infection of African Boxthorn, suggesting the plant acts as a green bridge plant. It is highly recommended that this plant be eradicated within the vicinity of potatoes and other Solanaceous crops.

Lethal wilt (LW), known as “Marchitez Letal” in Colombia, is an endemic disease affecting oil palms (Elaeis guineensis Jacq.) and a leading cause of crop loss. The disease is characterized by the drying of leaflets from the tip to the base, primarily impacting the lower third of the plant and progressively moving upward. This progression leads to physiological disturbances, including necrosis at the tips of immature inflorescence bracts (spines) and the detachment of bunch fruits, ultimately causing wilting. As a phytosanitary measure, infected palms are eradicated to prevent further spread of the disease. The primary goal of this research was to identify the bacteria associated with LW and to validate a molecular detection method. A 16S amplicon-based analysis was employed to identify and compare the microbial diversity in LW-affected palm tissues with those of healthy plants. Among the 16 OTUs corresponding to different bacterial genera found in all LW samples, taxonomic classification and symptomatology suggested that the bacteria closely associated with LW belong to the genus ‘Candidatus Liberibacter’. Further phylogenetic analysis indicated that these bacteria are part of the Rhizobiaceae family, grouping closely with other species of the genus ‘Ca. Liberibacter’. The concentration of the pathogen in different oil palm tissues was determined using droplet digital PCR and quantitative PCR, expressed in copies/μl in the LW samples. This study represents the first report of ‘Ca. Liberibacter’ sp. being associated with lethal wilt in oil palms of the Arecaceae family in Colombia. The findings from this research could contribute significantly to the development of effective management strategies to prevent crop losses. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .