Publications

4871

A novel hyperthermophilic, heterotrophic and anaerobic archaeon, designated strain SLHALR2 T , was isolated from the ‘Cooking Pots’ hot springs at Hell’s Gate, Tikitere, New Zealand. During the exponential growth phase, cells of strain SLHALR2 T appear as long, thin rods to filaments, measuring 0.25–0.4 µm in width and 3.0–7.0 µm in length. Strain SLHALR2 T grows at temperatures ranging from 60 to 97 °C (optimum 80–85 °C), at pH values between 5.0 and 7.3 (optimum pH 6.0) and with 0–8 g l −1 sodium chloride concentration (optimum 0–1.0 g l −1 ). Elemental sulphur is reduced to hydrogen sulphide. Strain SLHALR2 T is an obligate organotroph capable of utilizing a variety of proteinaceous substrates and a limited range of sugars. Archaeal cell extracts improve growth but are not mandatory for growth. Phylogenetic analysis based on 16S rRNA gene sequence comparisons indicates that strain SLHALR2 T belongs to the genus Infirmifilum within the family Thermofilaceae , order Thermofilales (phylum Thermoproteota ). The strain shares 98.4–99% 16S rRNA gene sequence similarity with described Infirmifilum species. Despite this high level of 16S rRNA gene similarity with recently described Infirmifilum species, both average nucleotide identity (71–74%), average amino acid identity (67–75.5%) values and digital DNA–DNA hybridization values support the designation of strain SLHALR2 T as a distinct species within Infirmifilum . Based on phylogenomic analyses and the physiological characteristics of the novel isolate, strain SLHALR2 T is proposed as the type strain of a new species, Infirmifilum tikiterense sp. nov. (=OCM2026=UBOCC M-3571), and an emended description of the genus Infirmifilum is proposed.

ABSTRACT Citrus greening disease, associated with the bacterium Candidatus Liberibacter asiaticus ( C Las), has severely impacted citrus yields on a global scale. C Las is vectored by the Asian citrus psyllid, Diaphorina citri Kuwayama, in a circulative and propagative manner. Extensive application of chemical insecticides for suppression of psyllid populations has resulted in widespread resistance. Despite considerable effort and expenditure, citrus greening disease continues to impair citrus production. For transmission to occur, C Las must bind and infect the psyllid vector via the gut epithelium, but little is known of the specific molecular interactions involved. By screening a phage display library, we selected ten psyllid gut binding peptides, a subset of which have sequence similarity to C Las surface proteins. Peptide binding to the surface of the psyllid gut epithelium was confirmed by identification of gut proteins bound by specific peptides. We evaluated whether these peptides could interfere with the interaction between C Las and the gut epithelium of D. citri , thereby impeding pathogen transmission. Peptide DcNy2 significantly reduced C Las acquisition and inoculation by D. citri compared to control treatments. Nymphs fed specific peptides exhibited reduced C Las acquisition and infection of both the alimentary canal and salivary glands without negatively impacting psyllid fecundity, development, or survival. These results support peptide-mediated disruption of C Las transmission by D. citri as a potential component of integrated strategies to manage citrus greening disease. IMPORTANCE Citrus greening disease, or huanglongbing, causes billions of dollars in losses and represents one of the greatest challenges facing global citrus production. Despite significant investment on multiple fronts, effective disease management strategies are lacking. This study shows for the first time that short peptides that bind to the surface of the gut of the Asian citrus psyllid vector interfere with C Las association with the gut. This critical first gut binding step is required for C Las to infect and propagate within the psyllid vector. The downstream consequence of this peptide-mediated interference is reduced acquisition and transmission of the citrus pathogen. This work provides the foundation for new transgenic or paratransgenic tools for use in the management of citrus greening disease.

Abstract Huanglongbing (HLB), primarily induced by the phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas), poses a significant threaten to citrus production worldwide. CLas deploys Sec-dependent effectors (SDEs) to manipulate host cellular processes, yet the underlying virulence mechanisms remain incompletely understood. Here, we identify SDE4580, a conserved CLas effector localized to the plant plasma membrane, as a key virulence factor that promotes pathogen proliferation and suppresses host immunity across citrus and Arabidopsis. Transcriptomic analysis reveals that SDE4580 reprograms membrane-associated biological processes and defense responses. Through yeast two-hybrid screening and biochemical validation, we demonstrate that SDE4580 physically interacts with the citrus vesicle trafficking regulator CsPRA1.E, a Prenylated Rab Acceptor 1 family protein. Functional assays establish CsPRA1.E as a positive regulator of immunity that promotes apoplastic secretion of defense-related proteins and enhances resistance to Xanthomonas citri subsp. citri. Crucially, SDE4580 antagonizes CsPRA1.E-mediated resistance by suppressing defense protein secretion without inducing target degradation. These findings uncover a novel pathogenic strategy whereby CLas subverts host endomembrane trafficking to disarm plant immunity. Targeting the SDE4580-CsPRA1.E interface may offer a promising avenue for developing durable HLB control strategies.

The spread of the reed planthopper Pentastiridius leporinus and its associated pathogens Candidatus Arsenophonus phytopathogenicus (ARSEPH) and Candidatus Phytoplasma solani (PHYPSO) increasingly threatens sugar beet production in Central Europe. Current surveillance systems rely mainly on vector monitoring, visual field assessments and molecular diagnostics of individual vectors and plants, all of which provide valuable but spatially limited information. This study evaluated sugar beet pulp samples generated during routine factory quality assessment as a large- scale surveillance resource for PHYPSO. During the 2025/26 campaign, 4887 pulp samples representing 1954 delivery field locations were collected, of which 1237 samples of individual field locations with consistent beet quality parameters were analyzed by direct PCR. PHYPSO was detected in 214 samples (17.3%). The molecular workflow was not subgroup-specific and did not include genotyping; therefore, PHYPSO-positive samples could not be assigned to individual 16SrXII subgroups. Comparison with visual field assessments showed that 85.7% of positive molecular detections originated from fields without visible symptoms. A carry-over experiment demonstrated that pathogen-derived DNA may persist across consecutive samples under worst-case conditions and must therefore be considered during data interpretation. In contrast, ARSEPH was detected by direct PCR in only six of 1237 samples (0.5%), all originating from the Euskirchen growing region. Comparison with qPCR, single-beet diagnostics and the carry-over experiment indicated insufficient sensitivity of the current ARSEPH direct-PCR assay; therefore, the observed detection rate should not be interpreted as true pathogen prevalence. Nevertheless, the observed spatial distribution patterns of monitoring sites indicate that industrial pulp sample monitoring substantially expands surveillance coverage beyond conventional symptom-based approaches and can help identify regions warranting further epidemiological investigation.

‘Candidatus Liberibacter solanacearum’ (Lso) haplotype D, transmitted by the carrot psyllid Bactericera trigonica, is a major threat to carrot production, particularly in the Mediterranean Basin and the Middle East. We investigated the impact of plant age at the time of inoculation on symptom development and yield under greenhouse and outdoor conditions. In greenhouse trials, 1- and 2-month-old plants were inoculated with psyllids harboring Lso. Both age groups showed reduced taproot weight compared with controls, but younger plants were more severely affected, exhibiting 90% yield reduction, while 2-month-old plants showed a 30% reduction. Witches’ broom symptoms appeared earlier in plants inoculated at 1 month (5 weeks postinoculation); however, within 2 weeks, plants inoculated at 2 months reached comparable levels of symptom incidence and severity. Additional greenhouse experiments using Lso-free psyllids confirmed that yield losses and disease symptoms were specifically due to Lso infection and not psyllid feeding. In outdoor trials, we tested the effects of inoculation at 7, 11, 15, and 19 weeks postsowing (wps) on disease incidence and yield. Significant yield losses occurred only in plants inoculated at 7 and 11 wps, with up to 45% reduction by harvest time. Symptoms began to appear at 20 wps in plants inoculated at 7 and 11 wps. At 23 wps, symptoms also appeared in plants inoculated at 15 wps, with a similar incidence to that observed in the earlier inoculation groups. Molecular detection of Lso at harvest (23 wps) confirmed that all plants inoculated at 19 wps or earlier were infected. These results demonstrate that carrots are highly susceptible to Lso-induced yield losses at the earlier stages of growth and highlight the importance of managing early season vector pressure to minimize economic damage.