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idw - Informationsdienst
Wissenschaft
To the point:
• Pseudomonas fluorescens SBW25 repeatedly evolves mat-like structures at an air–liquid interface within a few days in the lab.
• The original, ancestral type colonises the interface first and modifies the environment, helping mutants establish.
• The resulting “dispersal-driven” dynamics favour coexistence of many adaptive types, rather than a single classic selective sweep.
• The process is driven by a sessile–motile phenotype switch regulated via c-di-GMP.
As in a batch of kombucha or a barrel of sherry, microbes can assemble into a mat-like layer at the boundary between air and liquid. In laboratory culture, the bacterium Pseudomonas fluorescens SBW25 is widely known for doing exactly that: starting from a non-mat-forming original type, it evolves — through genetic mutations — into forms that construct a mat at the air–liquid interface, and it does so with striking regularity within just a few days.
For a long time, however, the ecological and physical mechanisms behind this reliability were not well understood. A team from the Department of Microbial Population Biology at the Max Planck Institute for Evolutionary Biology has now clarified what underpins the process. Using a combination of microscopy and mathematical modelling, they identify a critical, and somewhat counterintuitive, role for the original ancestral type: it transiently colonises the air–liquid interface first, effectively scaffolding the environment in ways that facilitate the evolutionary success of mat-forming mutants. In monoculture — without the original ancestor present — mat-forming mutants typically fail.
This shifts the emphasis from “the mutant alone” to the context the population creates for itself. The work highlights how closely evolution and ecology can be intertwined: early colonisers modify conditions, and successors depend on those transient changes to gain a foothold.
The study also reframes what evolutionary “success” looks like genetically. Rather than a classic selective sweep — in which a small number of adaptive types quickly dominate — the dynamics are “dispersal-driven”. As ancestors gradually disperse away from the interface, many adaptive types can co-occur and coexist within a single evolved population, producing high genetic diversity where one might expect a single winner.
Underlying these dynamics is a fundamental behavioural switch: dispersal versus stay-at-home. The evolutionary sequence is driven by phenotype switching between these two states mediate by c-di-GMP — a secondary signalling molecule.
Prof. Dr. Paul Rainey
Scientific Member (Director)
Department Microbial Population Biology
Max Planck Institute for Evolutionary Biology
Karita Y, Rodríguez-Sánchez GT, Brambilla E, Hernandez-Beltran JCR, Schwarz M, Rainey PB. 2026 Context-dependent adaptation in structured environments. Proc. R. Soc. B 293: 20252004. https://doi.org/10.1098/rspb.2025.2004
at formation by Pseudomonas fluorescens in unshaken laboratory cultures.
Source: Yuya Karita
Copyright: Ⓒ Yuya Karita
Criteria of this press release:
Journalists
Biology
transregional, national
Research results, Transfer of Science or Research
English
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