Publications

4994

Abstract Background Spirochetes are the most abundant bacterial group in the hindgut of termites. The largest species, with cell lengths of up to 100 µm, have been provisionally classified in the family “ Pillotinaceae ” based exclusively on morphological traits. However, in the absence of cultured representatives, their phylogenetic position and metabolism remain entirely unknown. Results We investigated phylogeny and metabolic capacities of “pillotinaceous” spirochetes using single-cell techniques, electron microscopy, and fluorescence in situ hybridization. All sequences of large spirochetes obtained from various termites fell into four distinct, well-supported clusters within the family Breznakiellaceae . Based on ultrastructural features, three of the clusters were assigned to the genera Pillotina , Hollandina , and the newly established genus Hollandinoides; a fourth cluster was tentatively assigned to the genus Clevelandina . Functional analysis of the single-cell genomes of Pillotina corrugata sp. nov., Hollandina grandis sp. nov., and Hollandinoides gharagozlouae gen. nov. sp. nov., combined with comparative genomics of other uncultured relatives, demonstrated differences in the capacity to degrade cellulose, hemicelluloses, and dextrins. While members of the genus Pillotina have a fermentative metabolism, members of the other genera encode a Wood–Ljungdahl pathway and, in the case of Hollandina , a group-III nitrogenase, suggesting roles in reductive acetogenesis and nitrogen fixation. Conclusions Our results provide the first molecular data on pillotinaceous spirochetes. We show that the three genera covered in our study belong to the family Breznakiellaceae , which harbors the majority of termite-gut spirochetes. Comparative genome analysis indicated that the large spirochetes in termite guts have distinct roles in symbiotic digestion.

<p>Huanglongbing (HLB), caused by <em>Candidatus </em>Liberibacter asiaticus (CLas), continues to challenge citrus production in Saudi Arabia. Although HLB is widespread, there is still limited understanding of how temperature, season, host species, and the type of tissue sampled influence the reliability of CLas detection. In this regard, 123 CLas-positive samples sourced from major citrus-growing areas were analyzed. These samples included data from 4 major citrus species and 4 tissue types. Additionally, cycle threshold<strong> </strong>(Ct) values obtained through quantitative PCR for each sample were used to examine how climate and CLas interact in bacterial detection. As lower Ct values indicate higher bacterial abundance, an analysis of covariance (ANCOVA) was conducted to assess the influence of season, tissue type, citrus species, and average seasonal temperature on Ct values. The results demonstrated significant differences among tissue types, with petiole and midrib tissues exhibiting consistently lower Ct values. Additionally, lower Ct values were observed in spring and autumn, and higher Ct values in warmer summers and colder winters, based on average temperatures. Among the citrus species, only <em>Citrus limon</em> illustrated a prominent increase in CLas levels as temperatures increased. CLas levels in <em>C. limon</em> showed only minor fluctuations with temperature. Taken together, these results indicated that temperature gradients strongly shape CLas population levels in Saudi Arabia and influence the reliability of pathogen detection. Considering climatic context, along with tissue type and season can substantially improve sampling strategies and enhance the effectiveness of HLB monitoring programs in arid and semi-arid citrus production systems.</p>

ABSTRACT Endemic to the deep subsurface biosphere sulphate‐reducing ‘ Desulforudis audaxviator ’ has been called a living microbial fossil due to the high nucleotide sequence identity of its genomes across continents. Evolutionary stasis of this bacterium was established based on the analysis of metagenome assembled genomes, single cell genomes and a single axenic culture. The lack of high‐quality reference genomes necessitates efforts to cultivate and isolate pure cultures that could shed light on the hypothetical slow evolution of Desulforudis ‐clade bacteria deep underground. Molecular signatures demonstrated the presence of Desulforudis ‐like phylotypes in subsurface environments worldwide. Here we report the isolation of four novel strains of the Desulforudis ‐clade, all belonging to Desulfosceptrum tomskiensis gen. nov. sp. nov. Four strains of the new species were isolated from deep boreholes in Western Siberia, separated by hundreds of kilometres. Genome comparisons revealed minimal differences between these strains, with average nucleotide sequence identity (ANI) values above 99.9%, low number of SNPs, and near‐identical CRISPRs. The bacterium, together with Desulforudis audaxviator BYF T gen. nov. sp. nov., deposited in international culture collections, provides a bases for understanding the slow evolution of Bacillota endemic to the deep biosphere.

Areca palm yellow leaf phytoplasma (AYLP) and Areca palm velarivirus 1 (APV1) are two critical pathogens associated with yellow leaf in areca palm, resulting in devastating damage to areca production. However, evidence of their coinfection remains unclear. Areca palms showing yellow leaf symptoms (suspected to be caused by phytoplasma and velarivirus 1) were surveyed and sampled around Hainan Island of China, and the pathogens were identified and analyzed in the study. The results showed that infectious leaf yellowing symptoms of areca palms primarily occurred in eastern and southern cities and counties of Hainan Island. Molecular identification revealed coinfection of ‘Candidatus Phytoplasma asteris’ (16SrI-B subgroup) and APV1 in individual areca palm samples. Among 520 samples tested by qPCR, AYLP was detected in 23.46% (n = 122), APV1 in 53.46% (n = 278), and a coinfection with both AYLP and APV1 in 10.96% (n = 57). A statistically significant difference in APV1 detection rate was observed between asymptomatic and symptomatic plantations (P < 0.0001), suggesting that APV1 infection likely represents an important risk factor for yellowing development in cultivated areca palm populations. These results confirm the coinfection of AYLP and APV1 on Hainan Island, offering epidemiological evidence for targeted disease management.