Conclusive identification of EPS-derived depletants mediating smectic-like bundle formation under starvation

Determine which specific extracellular polymeric substances mediate the depletion attraction responsible for smectic-like bundle formation in planktonic Escherichia coli under nutrient starvation, and establish conclusively the roles of curli amyloid fibers and outer membrane vesicles in this mechanism.

Background

The study reports that nutrient starvation causes planktonic Escherichia coli to form smectic-like bundle clusters and presents evidence that extracellular polymeric substances (EPS) and growth arrest are both involved. Using BisBAL to comprehensively reduce EPS secretion significantly inhibited bundle formation, suggesting EPS-mediated depletion attraction as a key mechanism.

The authors specifically examined curli and outer membrane vesicles (OMVs) as candidate depletants. Curli-deficient mutants still formed bundles, and fluorescence imaging did not show an appreciable amount of OMVs between bundles; however, the authors were unable to determine the relevance of curli and OMVs conclusively, leaving the precise identity of the depletant(s) unresolved.

References

Further investigation is required for elucidating what specific substances are most relevant to the depletion attraction involved. In this work, we inspected two specific substances, curli and OMVs, but could not determine their relevance conclusively.

— Smectic-like bundle formation of planktonic bacteria upon nutrient starvation  (2407.05031 - Shimaya et al., 2024) in Conclusions