100-Micrometer Bacterium with Mystery 45-μm Tubes Reshapes Textbook Definition of "Prokaryote"

Forum topic · ✨步子哥 · 2026-08-06

Summary

A September 2025 paper in npj Imaging reports an entirely novel intracellular structure inside Profftella armatura, a defensive bacterial symbiont of the Asian citrus psyllid (Diaphorina citri). Using SBF-SEM, HVET, and FISH, a Korean–Japanese team observed 1–43 tubular filaments per cell, each up to 45 μm long and ~230 nm wide, occupying ~6.3–7% of cell volume. Each tube is built from 5–6 fine fibers twisted into a right-handed helix, resembling a steel cable. The structures survive detergent lysis without chemical fixation or resin embedding, indicating unusual mechanical stability. Ribosomes cluster near the tubes, hinting at roles in protein synthesis and mechanical support for cells elongated up to 136 μm. The paper labels the structure "enigmatic"—its composition, biogenesis, and function are unknown. The finding further erodes the textbook claim that prokaryotes lack membrane-bound organelles, joining bacterial microtubules (2019), magnetosomes, carboxysomes, and liquid–liquid phase separation as evidence that bacterial interiors are richer than the classical definition suggests.

Key points

Source: Song C. et al., "Enigmatic tubular ultrastructure in the bacterial defensive symbiont of the Asian citrus psyllid *Diaphorina citri*," *npj Imaging*, 18 Sep 2025. DOI: 10.1038/s44303-025-00107-w
Organism: *Profftella armatura*, an obligate intracellular defensive symbiont living in the bacteriome of the Asian citrus psyllid (*Diaphorina citri*, ~3 mm). It coexists with *Carsonella ruddii*, the nutritional symbiont.
Cell scale: Observed cells range 2.8–136 μm in length and 2–5 μm in width—visible to the naked eye, larger in diameter than a human hair (~70 μm).
The tubes: 1–43 per cell, each up to 45 μm long, ~230 nm in diameter, occupying ~6.3% of cytoplasm and stabilizing near 7% once cell volume exceeds 80–90 μm³.
Architecture: 5–6 fine fibers twisted into a right-handed helix, analogous to a steel cable or tug-of-war rope.
Stability: Tubes retain morphology after detergent lysis without chemical fixation or resin embedding, under high vacuum in EM—suggesting exceptional mechanical robustness.
Imaging methods: Serial block-face SEM (SBF-SEM), high-voltage electron tomography (HVET), and fluorescence in situ hybridization (FISH).
Ribosome association: Ribosomes cluster around the tubes, leading the authors to hypothesize possible roles in protein-synthesis organization (analogous to rough ER) and mechanical support for the elongated cell (analogous to a cytoskeleton).
Hypotheses (non-exclusive):
Unknowns: chemical composition, biogenesis pathway, phylogenetic spread, exact function—authors use "enigmatic," "implies," and "may" deliberately.
Why it matters: The textbook contrast between prokaryotes ("simple," no membrane-bound organelles) and eukaryotes is eroding. Bacterial microtubules (2019), magnetosomes, carboxysomes, and liquid–liquid phase separation already chipped at it; the Profftella tubes add a *novel*, unclassified structure with no known homolog.
Evolutionary context: Obligate intracellular symbiosis imposes severe reductive pressure (Carsonella has a ~160 kb genome with <200 genes). Genome reduction has not produced "simplicity" in *Profftella*—instead, an unprecedented internal architecture emerged. The article draws parallels to engineering and AI: steel cables, suspension-bridge cables, MoE, sparse attention, and LoRA all achieve more with less by reorganizing existing parts.
Practical angle: Authors suggest disrupting the tubes could compromise psyllid defense, offering a possible pest-control lever against Huanglongbing ("citrus AIDS") transmission.

100-Micrometer Bacterium with Mystery 45-μm Tubes Reshapes Textbook Definition of "Prokaryote"

Summary

Key points

Tags