Publications

4545

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.

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.