Interplay of motility and polymer-driven depletion forces in the initial stages of bacterial aggregation
Motile bacteria are often found in complex, polymer-rich environments in which microbes can aggregate via polymer-induced depletion forces. Bacterial aggregation has many biological implications; it can promote biofilm formation, upregulate virulence factors, and lead to quorum sensing. The steady state aggregation behavior of motile bacteria in polymer solutions has been well studied and shows that stronger depletion forces are required to aggregate motile bacteria as compared with their nonmotile analogs. However, no one has studied whether these same trends hold at the initial stages of aggregation. We use experiments and numerical calculations to investigate the polymer-induced depletion aggregation of motile Escherichia coli in polyethylene glycol solutions on short experimental timescales (∼10 min). Our work reveals that in the semi-dilute polymer concentration regime and at short timescales, in contrast to what is found at steady state, bacterial motility actually enhances aggregate formation by increasing the collision rate in viscous environments. These unexpected findings have implications for developing models of active matter, and for understanding bacterial aggregation in dynamic, biological environments, where the system may never reach steady state.
© 2019 The Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. The article was received on 17 Apr 2019, accepted on 29 Jul 2019 and first published on 23 Aug 2019. Conflicts of interest: The technology described in this publication is the subject of a patent application filed by Caltech. This work was funded in part by the Army Research Office (ARO) Multidisciplinary University Research Initiative (MURI) contract #W911NF-17-1-0402, the Jacobs Institute for Molecular Engineering for Medicine, an NSF Graduate Research Fellowship DGE-144469 (to APS), and a Center for Environmental Microbial Interactions (CEMI) Caldwell Graduate Fellowship (to APS). We thank Andres Collazo and the Beckman Imaging Facility for help with imaging, and we thank Natasha Shelby for contributions to writing and editing this manuscript.
Published - c9sm00791a.pdf
Supplemental Material - c9sm00791a1_si.pdf