Confinement discerns swarmers from planktonic bacteria.

Powered by flagella, many bacterial species exhibit collective motion on a solid surface commonly known as swarming. As a natural example of active matter, swarming is also an essential biological phenotype associated with virulence, chemotaxis, and host pathogenesis. Physical changes like cell elongation and hyper-flagellation have been shown to accompany the swarming phenotype. Less studied, however, are the contrasts of collective motion between the swarming cells and their counterpart planktonic cells of comparable cell density. Here, we show that confining bacterial movement in circular microwells allows distinguishing bacterial swarming from collective swimming. On a soft agar plate, a novel bacterial strain Enterobacter sp. SM3 in swarming and planktonic states exhibited different motion patterns when confined to circular microwells of a specific range of sizes. When the confinement diameter was between 40 µm and 90 µm, swarming SM3 formed a single-swirl motion pattern in the microwells whereas planktonic SM3 formed multiple swirls. Similar differential behavior is observed across several other species of gram-negative bacteria. We also observed 'rafting behavior' of swarming bacteria upon dilution. We hypothesize that the rafting behavior might account for the motion pattern difference. We were able to predict these experimental features via numerical simulations where swarming cells are modeled with stronger cell-cell alignment interaction. Our experimental design using PDMS microchip disk arrays enabled us to observe bacterial swarming on murine intestinal surface, suggesting a new method for characterizing bacterial swarming under complex environments, such as in polymicrobial niches, and for in vivo swarming exploration.

Bacterial Flagellins: Does Size Matter?

The bacterial flagellum is the principal organelle of motility in bacteria. Here, we address the question of size when applied to the chief flagellar protein flagellin and the flagellar filament. Surprisingly, nature furnishes multiple examples of 'giant flagellins' greater than a thousand amino acids in length, with large surface-exposed hypervariable domains. We review the contexts in which these giant flagellins occur, speculate as to their functions, and highlight the potential for biotechnology to build on what nature provides.

Polar, peritrichous, and lateral flagella belong to three distinguishable flagellar families.

The bacterial flagellum transforms its shape into several distinguishable helical shapes (polymorphs) under various environmental conditions. Polymorphs of each type of flagellum stay on a circle in the pitch-diameter (P versus piD) plot, indicating that they all belong to one family. Previously, we showed that the flagellar family of a marine bacterium Idiomarina loihiensis (Family II) differed from the conventional flagellar family of Salmonella typhimurium (Family I). The pitch and diameter of Family II flagella are half those of Family I flagella. We have suggested that Family I encompasses peritrichous flagella, while Family II forms a polar flagellum. In this study, we have surveyed the polymorphs of flagella from 18 other species and categorized their family types. Previous observations were confirmed; Family I form peritrichous flagella and Family II form polar flagella. Furthermore, we found that lateral flagella had helical parameters much smaller than those of the other two Families and thus belong to a new family (Family III).

Telonema antarcticum sp. nov., a common marine phagotrophic flagellate.

Telonema is a widely distributed group of phagotrophic flagellates with two known members. In this study, the structural identity and molecular phylogeny of Telonema antarcticum was investigated and a valid description is proposed. Molecular phylogeny was studied using small-subunit rRNA (SSU rRNA) gene sequences. The pear-shaped cell had two subequal flagella that emerged laterally on the truncated antapical tail. One flagellum had tripartite hairs. The cell was naked, but had subsurface vesicles containing angular paracrystalline bodies of an unknown nature. A unique complex cytoskeletal structure, the subcortical lamina, was found to be an important functional and taxonomic feature of the genus. Telonema has an antero-ventral depression where food particles are ingested and then transferred to a conspicuous anterior food vacuole. The molecular phylogeny inferred from the SSU rRNA gene sequence suggested that Telonema represents an isolated and deep branch among the tubulocristate protists.

The soil flagellate Proleptomonas faecicola: cell organisation and phylogeny suggest that the only described free-living trypanosomatid is not a kinetoplastid but has cercomonad affinities.

The only putative free-living trypanosomatid is Proleptomonas faecicola described first by Woodcock in 1916 as a coprophilic flagellate with striking Leptomonas-like flagellar movement but lacking a kinetoplast. P faecicola was later identified by Sandon in 1927 as a widespread non-phagotrophic inhabitant of soils. No division stages were seen by either observer. An organism conforming to Woodcock's light microscope description has been isolated from tapwater and cultivated axenically in various serum-containing media. Division has been shown to occur in an aflagellate stage enclosed in a thin cyst wall. Electron microscopy of the flagellate stage reveals that, in addition to the long locomotory flagellum, a second non-motile flagellum is present attached to the body along its entire length. The flagellate's ultrastructure lacks all the major features of the Trypanosomatidae. The several mitochondria of Proleptomonas have tubular cristae and lie between intracytoplasmic microtubules originating as a loose cone associated with the flagellar basal bodies. This cytoskeleton is much reduced in the division cyst. A comparable Proleptomonas-like flagellate with similar division cysts has been observed in soil samples from farmland. Phylogenetic analysis based on SSU rRNA gene sequences suggests that the cultured organism identified here as Proleptomonas is unrelated to the Kinetoplastida and has affinities with the Phylum Cercozoa Cavalier-Smith, even though in morphology, life cycle and mode of feeding it bears little resemblance to any member of that diverse grouping.

Sequence typing confirms that Campylobacter jejuni strains associated with Guillain-Barré and Miller-Fisher syndromes are of diverse genetic lineage, serotype, and flagella type.

Guillain-Barré syndrome (GBS) and Miller-Fisher syndrome (MFS) are correlated with prior infection by Campylobacter jejuni in up to 40% of cases. Nucleotide sequence-based typing of 25 C. jejuni isolates associated with neuropathy permitted robust comparisons with equivalent data from approximately 800 C. jejuni isolates not associated with neuropathy. A total of 13 genetic lineages and 20 flaA short variable region nucleotide sequences were present among the 25 isolates. A minority of isolates (4 of 25) had the flaA short variable region nucleotide sequences that were previously proposed as a marker for GBS-associated isolates. These 4 isolates probably represented the Penner serotype 19 lineage, which has been proposed to have an association with GBS.