Publications

4947

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 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.