Publications

4851

Phytoplasmosis associated with the ‘Candidatus Phytoplasma solani’ subgroups 16SrXII-A and 16SrXII-P (Mollicutes) poses a threat to European sugar beet cultivation, alongside the “basses richesses” syndrome caused by ‘Ca. Arsenophonus phytopathogenicus’ (Gammaproteobacteria). Both subgroups co-occur in sugar beet and have been detected in Pentastiridius leporinus, a polyphagous planthopper associated with SBR-affected fields. Despite ongoing monitoring of disease spread and pathogen characterization, approaches for direct subgroup differentiation remain limited. Consequently, discriminative conventional PCR assays targeting secY were developed, with detection limits estimated using synthetic gene fragments. Assay performance was assessed using 900 DNA templates from sugar beet from Germany and neighboring countries, 50 German red beet samples, and 320 planthoppers. Distinct amplicon sizes of 549 bp and 857 bp enabled reliable detection and differentiation of 16SrXII-A and 16SrXII-P, respectively. Detection rates were broadly concordant with those obtained using an established phytoplasma detection approach. Estimated detection limits were 100 target copies for 16SrXII-A and 1000 for 16SrXII-P. Assay application indicated more frequent detection of 16SrXII-P in samples from Germany and of 16SrXII-A in those from neighboring countries. The assays provide a rapid and accessible tool for subgroup differentiation and may facilitate large-scale epidemiological surveillance and future studies of host tolerance.

Abstract Geothermal systems harbor abundant novel microorganisms, representing substantial phylogenetic and functional diversity among yet‐to‐be‐cultivated bacteria with significant ecological roles. Nevertheless, research on the diversity, metabolic potential, and evolutionary history of these uncultured taxa remains limited. In this study, 19 metagenome‐assembled genomes (MAGs) were recovered from hot springs in Tengchong, Yunnan Province. Phylogenetic analyses indicate that these MAGs form sister lineages to an existing clade, leading to their proposed classification within three novel phyla: Yinglongibacterota , Xuanmingibacterota , and Gonggongibacterota , named after figures from the traditional Chinese legend, Classics of Mountains and Seas. Sequence analysis of both hot spring‐derived and published MAGs reveals that all three phyla exhibit similar facultative anaerobic lifestyles. Multiple substrates, including cellulose, glucan, pectin, and xylan, can be degraded by these phyla, especially Gonggongibacterota , suggesting their critical role in converting complex plant matter into more readily degradable substrates and contributing to sugar fermentation. Furthermore, the ability of these phyla to reduce selenite facilitates environmental detoxification. Notably, gene loss events have resulted in widespread auxotrophy for heme and biotin in these lineages, which may indicate microbial cross‐feeding in the community as an adaptation strategy. These pioneering results provide a comprehensive overview of the taxonomic and metabolic characteristics of the three novel phyla, offering insights into their ecological significance and guiding future cultivation efforts.

Rapid and accurate diagnosis of ‘ Candidatus Phytoplasma’ is critical for disease management but remains challenging due to the pathogen's unculturable nature, low titers, uneven distribution, and genetic complexity. Although current official guidelines provide a highly adaptable taxonomic foundation for species assignment, translating these broad recommendations into standardized routine diagnostics remains difficult. This study implemented the established species assignment guidelines by developing a structured, proof-of-concept diagnostic framework utilizing a multilocus sequence analysis workflow coupled with Oxford Nanopore Technologies (ONT) sequencing. The developed workflow targets four barcodes—16S, secA, rplV, and tufB—and replaces fixed demarcation criteria with a best-match principle for non-16S barcodes. Furthermore, the study offers guidance for barcode selection and challenges the use of 16S rRNA sequencing as a sole screening assay. Moreover, a read-based quantification system incorporating control thresholds was implemented to provide an objective and reliable assessment of the results. The workflow was validated using a spiked dilution series and naturally infected samples, demonstrating that the ONT workflow achieves sensitivity and accuracy comparable to, or exceeding, that of traditional Sanger sequencing. Although PCR multiplexing was found to reduce sensitivity, limiting the immediate throughput advantages over Sanger sequencing, the proposed framework offers significant value through flexible species assignment and stringent contamination controls. Consequently, this method serves as a robust, high-resolution tool for resolving complex phytoplasma infections. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

The distribution of ‘Candidatus Phytoplasma prunorum’, a phloem-limited pathogen, varies among plant tissues during the year, but knowledge about quantitative comparisons of its presence in roots and above-ground tissues across Prunus species remains limited. The variation in ‘Ca. P. prunorum’ in four Prunus species was monitored monthly during 2025 using quantitative PCR-based absolute quantification. Roots, one-year-old shoots and annual shoots were sampled monthly from 21 infected trees of Prunus armeniaca, Prunus domestica, Prunus persica and Prunus salicina. Phytoplasma titer varied with plant part and sampling month, and differences were also observed among the examined host groups. Because cultivar and rootstock were linked to species, these differences cannot be attributed to species alone. Roots provided the most consistent year-round detection, whereas above-ground tissues showed stronger monthly variation during the studied period. P. domestica displayed the most distinct pattern: roots remained frequently positive, while one-year-old shoots and particularly annual shoots had lower detection rates and lower phytoplasma titers. Multilocus genotyping detected ten multilocus profiles, but their uneven distribution among only 21 trees precluded a reliable evaluation of their relationship with phytoplasma titer or symptom expression.

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 Syndrome Basses Richesses (SBR) is a phloem-limited disease of sugar beet caused by ‘ Candidatus Arsenophonus phytopathogenicus’ (ARSEPH), a bacterium currently considered a facultative endosymbiont of its insect vector, Pentastiridius leporinus . Due to increasing disease incidence and the need for reliable vector-free resistance screening methods, this study evaluated alternative ARSEPH transmission routes using chip grafting and the parasitic plant dodder ( Cuscuta campestris ). Given that Arsenophonus species are unculturable and their insect vectors have complex life cycles so laboratory propagation is labor intensive, the development of vector-independent systems is desirable for controlled pathogen transmission and host–pathogen interaction studies. Chip grafting enabled successful ARSEPH transmission to sugar beet, though with low efficiency (~ 9.6%) and delayed pathogen detection. While C. campestris acquired and maintained high ARSEPH titers, it failed to transmit the bacterium to healthy plants, indicating limited systemic movement. In contrast, vector-mediated transmission via P. leporinus achieved 100% efficiency within 25 days, confirming a strong biological compatibility. These findings underscore the limitations of non-vector-based approaches for phloem-restricted pathogens and highlight the need for methodological optimization. The study provides key insights into ARSEPH’s complex transmission biology and supports a functionally specialized association with its insect vector.

Abstract Phytoplasma diseases are threat to sesame and its wild relatives, but information on their occurrence in exotic Sesamum species is limited. During field evaluation, Sesamum angolense , S. angustifolium , and S. latifolium exhibited characteristic phyllody and witches' broom symptoms, including virescence, leafy floral organs, polysepalous calyx, polypetalous corolla, flattened stamens, shortened internodes, excessive shoot proliferation, and leaf twisting and curling. Molecular detection using universal phytoplasma primers P1/P7 and tuf gene-specific primers fTufAy/rTufAy amplified products of approximately 1.8 kb and 940 bp, respectively, from symptomatic plants. Sequence analysis of the 16S rRNA and tuf genes revealed 99–100% nucleotide identity with members of the 'Candidatus Phytoplasma asteris ' group. Phylogenetic reconstruction based on both loci consistently assigned the isolates to the 16SrI-B subgroup of 'Ca. Phytoplasma asteris'. To the best of our knowledge, this is the first report of phytoplasma infection in S. angolense , S. angustifolium , and S. latifolium , characterized at the strain level using both 16S rRNA and tuf gene sequences. The findings expand the known host range of 16SrI-B phytoplasmas and demonstrate that these wild Sesamum species, which are valuable components of the tertiary gene pool of cultivated sesame, can serve as natural reservoirs of phytoplasma inoculum.

During field surveys conducted in 2024 and 2025 in pepper production areas in Altunhisar distinct of Niğde province, Türkiye, plants showing phytoplasma-like symptoms were observed. A total of 25 symptomatic pepper samples were collected, and total nucleic acids were extracted using the CTAB method. The samples were analyzed for phytoplasma infection by PCR amplification of the 16S rRNA gene region. In addition, two asymptomatic pepper plants were included as negative controls. PCR analysis revealed that all samples showing symptoms produced amplicons of the expected size, while no amplification was obtained from the asymptomatic plants. Sequencing and phylogenetic analyses revealed that the detected phytoplasma belonged to the 16SrVI-A subgroup, corresponding to ‘Candidatus Phytoplasma trifolii’. The subgroup assignment was further confirmed by in silico (virtual) RFLP analysis of the 16S rRNA gene. The representative 16S rRNA gene sequence of one strain obtained in this study was deposited in the GenBank database (GenBank accession number PX885052). Based on the available literature, this study provides the first molecular evidence of ‘Candidatus Phytoplasma trifolii’ infection in pepper plants grown in Niğde province, Türkiye. The findings contribute to the current knowledge on the distribution of pepper-infecting phytoplasmas in Türkiye and emphasize the need for further epidemiological and vector-related studies.