Abstract
SummaryLess than a handful of cuboid and squared cells have been described in nature, which makes them a rarity. Here, we show how Candidatus Thiosymbion cuboideus, a cube-like gammaproteobacterium, reproduces on the surface of marine free-living nematodes. Immunostaining of symbiont cells with an anti-fimbriae antibody revealed that they are host-polarized, as these appendages exclusively localized at the host-proximal (animal-attached) pole. Moreover, by applying a fluorescently labeled metabolic probe to track new cell wall insertion in vivo, we observed that the host-attached pole started septation before the distal one. Similarly, Ca. T. cuboideus cells immunostained with an anti-FtsZ antibody revealed a proximal-to-distal localization pattern of this tubulin homolog. Although FtsZ has been shown to arrange into squares in synthetically remodeled cuboid cells, here we show that FtsZ may also mediate the division of naturally occurring ones. This implies that, even in natural settings, membrane roundness is not required for FtsZ function.
Highlights
Prokaryotic cells have evolved an enormous diversity of cell shapes and sizes
We discovered that in this ectosymbiont both FtsZ and newly synthesized peptidoglycan (PG) localize at the septum in a proximal-to-distal fashion, implying that symbiont growth starts at the hostattached pole and that the tubulin homolog may mediate septal PG insertion
The ectosymbiont of the marine nematode Catanema sp. ‘‘Guadeloupe’’ belongs to the candidate genus Candidatus Thiosymbion and bears the ftsZ gene To phylogenetically place the symbiont of the nematode Catanema sp. ‘‘Guadeloupe’’ and to characterize its metabolic potential, we dissociated it from its host, extracted its genomic DNA and sequenced
Summary
Most model bacteria are spheres or rod-like, recently more uncommon shapes, including corkscrews, crescents, or stars, are receiving increasing attention (Caccamo and Brun, 2017; Kysela et al, 2016). The rigid peptidoglycan (PG) layer of the cell envelope provides mechanical strength and determines the cell shape. Short MreB filaments are spiraling along the envelope to elongate the cell corpus, FtsZ polymerizes exclusively at the septal plane determining the end of the cell cycle (McQuillen and Xiao, 2020; Shi et al, 2018). In the case of model rods and cocci, FtsZ polymerizes into a discontinuous ring-like structure at septation onset or, at least, during its last step (Eswara and Ramamurthi, 2017). In synthetically remodeled cells, fluorescently tagged FtsZ could polymerize into other shapes (including squares), while displaying the usual dynamics (Soderstrom et al, 2018)
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