Chemotaxis towards autoinducer 2 mediates autoaggregation in Escherichia coli.

Leanid Laganenka,Remy Colin,Victor Sourjik

doi:10.1038/ncomms12984

Abstract

Bacteria communicate by producing and sensing extracellular signal molecules called autoinducers. Such intercellular signalling, known as quorum sensing, allows bacteria to coordinate and synchronize behavioural responses at high cell densities. Autoinducer 2 (AI-2) is the only known quorum-sensing molecule produced by Escherichia coli but its physiological role remains elusive, although it is known to regulate biofilm formation and virulence in other bacterial species. Here we show that chemotaxis towards self-produced AI-2 can mediate collective behaviour—autoaggregation—of E. coli. Autoaggregation requires motility and is strongly enhanced by chemotaxis to AI-2 at physiological cell densities. These effects are observed regardless whether cell–cell interactions under particular growth conditions are mediated by the major E. coli adhesin (antigen 43) or by curli fibres. Furthermore, AI-2-dependent autoaggregation enhances bacterial stress resistance and promotes biofilm formation.

Highlights

Autoinducer 2 (AI-2): LowHigh the OD595 of the solution was measured
We further show that this self-attraction is mediated by the quorum-sensing molecule autoinducer-2 (AI-2), the only quorum-sensing signal described for E. coli
Consistent with previous studies performed for other E. coli K-12 strains[8], under these conditions the high-density (OD600 of 2.0) culture of W3110 showed reproducible aggregation that was dependent on antigen 43 (Ag43) (Supplementary Fig. 1) but not on curli or on other biofilm matrix components, poly-beta-1,6-N-acetyl-D-glucosamine and colanic acid (Supplementary Fig. 2)

Summary

Results

Aggregation of E. coli depends on motility and chemotaxis. We first investigated aggregation of E. coli strain W3110 (RpoS þ )[12] grown at 37 °C to a mid-exponential growth phase. When cultures were incubated under conditions that enable aggregation, the induction of the Plsr-egfp reporter in the wild type—but not in the aggregation-deficient Dflu, DcheY or DlsrB mutants—increased significantly during the first 40 min (Fig. 4a) This was likely explained by the increased local accumulation of AI-2 in the aggregates, because the wild-type strain overexpressing LuxS showed a steadily high level of lsr operon expression. Consistent with previous reports[10,11], we observed that aggregation behaviour of cell grown at 30 °C to OD600 1⁄4 1.0 was dependent on curli, whereas flu deletion had only a moderate effect (Fig. 6a and Supplementary Fig. 11a) Despite this different mode of cell–cell interaction and lower expression of lsr operon at 30 °C (Supplementary Fig. 12a), the dependence of curli-mediated aggregation on motility and AI-2 chemotaxis was similar to the Ag43-mediated aggregation. Biofilm formation at 30 °C was affected by cheY and lsrB deletions, whereas flu deletion had lesser effect in this case (Fig. 6b), as confirmed by the crystal violet staining (Supplementary Fig. 12b) and quantification of the microcolony size distribution within biofilms (Supplementary Fig. 12c)

Discussion

Methods

Background