Functional impact of a type VI secretion system on RsmE-mediated spatial structure formation in Pseudomonas fluorescens Pf0-1

Authors

Wells, M., Evans, A., Srinivasa, S., Delprince, A., Santos, R., Garland, C., Valletta, A., Kim, W.

Abstract

Bacteria naturally form densely structured populations wherein both space and nutrients become locally limited. In densely populated Pseudomonas fluorescens Pf0-1 colonies, spatiogenetic patches with drastically reduced cellular density naturally emerge through spontaneous mutations in rsmE. RsmE is a posttranscriptional regulator that binds to specific mRNAs, including those that consequently repress the production of extracellular secretions. We have previously shown that delta-rsmE produces an extracellular polysaccharide (EPS) and biosurfactant that collectively function to define the spatiogenetic structure and locally outcompete the WT. Here, we identify additional RsmE-regulated secretions through a combination of RNA-sequencing and LC-MS/MS. In particular, a type VI secretion system (T6SS) was exclusively produced by delta-rsmE. Confocal microscopy imaging of WT and genetically modified delta-rsmE cocultures showed that the T6SS kills WT cells that invade the low-density spatiogenetic structure. However, its impact on competition with the WT was both quantifiably and spatially limited in the absence of the normally co-produced EPS and biosurfactant, largely due to the consequently altered spatial structure. These results highlight the importance of understanding both the individual and collective spatial functions of extracellular secretions, especially in the ecological context of densely structured microbial populations.

Preprint server: bioRxiv
The authors list and abstract were imported from bioRxiv on 30 Jul 2026.

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