Publications

4859

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.

‘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 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.

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.