Surfing or sliding: the act of naming and its implications

TL;DR

This paper discusses the implications of naming practices and responds to Kovács et al., exploring how naming influences perception and categorization in a specific context.

Contribution

It provides a critical analysis of naming conventions and their impact, offering new insights into the act of naming and its broader implications.

Findings

Naming significantly affects perception and categorization.

The act of naming has profound social and cognitive implications.

Responds to and critiques Kovács et al.'s findings.

Abstract

Reply to Kov\'acs et al.

Full text

Surfing or sliding: the act of naming and its implications

M. Hennes, J. Tailleur, Gaelle Charron, and Adrian Daerr1

Laboratoire Matière et Systèmes Complexes (MSC) UMR CNRS 7057, University Paris Diderot, 75205 Paris cedex 13, France

Kovàcs et al. have greatly contributed to the characterisation of sliding hoelscher2017 ; grau2015 ; pollitt2015 , a flagella-independent, ”passive type of [bacterial] movement, […] powered by the pushing force of dividing cells and additional factors facilitating the expansion over surfaces” hoelscher2017 . They suggest kovacs2017 that bacterial surfing hennes2017 should be described by the same name to ”facilitate the understanding between the biophysics and the microbiology communities”.

Providing a clear and systematic classification of bacterial modes of motility is indeed a common objective of both communities, but one still has to agree on the best way to proceed. Bacteria possess a surprisingly rich toolbox to interact with their environment and achieve motion: flagella, pili, surfactants, exopolysaccharide, etc henrichsen1972 . Because sliding and surfing share overlapping components, Kovàcs et al. suggest using a unique designation. On the contrary we advocate a characterisation and classification of surface translocation modes by their underlying physical and chemical mechanisms. The comparison with human motions speaks for itself: running, swimming, walking and biking all make use of legs, but the diversity of the underlying mechanisms and characteristics has naturally led to an equal diversity of designations.

Similarly, bacterial surfing and sliding indeed have little in common beyond requiring surfactant production:

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Sliding is powered by cell division henrichsen1972 ; harshey2003 ; hoelscher2017 while gravity is the driving force of surfing hennes2017 , the cells being only passengers of the sliding droplet.

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Sliding occurs at high cell density kinsinger2003 whereas the cell density remains far below close packing in surfing hennes2017 .

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Sliding speeds are reported to be typically around 2 $\upmu$m min*-1* - 5 $\upmu$m min*-1* henrichsen1972 ; harshey2003 ; seminara2012 , which is about 50 times smaller than typical surfing speeds (250 $\upmu$m min*-1* even on very shallow slopes).

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Sliding seems to rely on the production of an EPS matrix gestel2015 , which is not required in surfing (droplet depinning can be initiated even by pure surfactin or sugar drops hennes2017 ).

For all these reasons, we think using a common name would be a source of confusion, rather than clarity.

Our characterization of colony surfing has made its underlying mechanisms quite clear: an osmotic pumping makes a droplet containing bacteria inflate while surfactin directly lowers the surface tension and increases the wettability of the substrate, leading to the depinning of the droplet and hence to its sliding. Bacteria are then passively advected by the surrounding fluid, collectively ”surfing” on the sliding droplet.

On the contrary, obtaining a precise characterisation of the microscopic physical and chemical mechanisms underpinning sliding remains a challenge. This is apparent in the recent review of Hölscher and Kovàcs hoelscher2017 which highlights that ”sliding” describes translocation modes that may or may not require surfactant, and may or may not require EPS matrix. Further elucidation of the physico-chemistry of sliding could thus, in our opinion, lead to more precise characterisations of translocation modes which would only phenomenologically appear related: the entropy of our dictionary should only increase as our knowledge progresses.

Author contributions: MH, JT, GC and AD wrote the manuscript.

The authors declare no conflict of interest.

1 Corresponding author: adrian.daerr@univ-paris-diderot.fr