2024/05/14 by Jiyong Cheon, Kyu Hwan Choi, Cheon, Jiyong +9 · 3 citations
Agricultural and Biological Sciences · Chemical Engineering · Materials Science · #Chemical and Physical Properties in Aqueous Solutions #Crystallization and Solubility Studies #FOS: Physical sciences #Probiotics and Fermented Foods #Soft Condensed Matter (cond-mat.soft)
paper · pdf · doi:10.48550/arxiv.2405.08995
openalex publication_date 2024/05/14 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We study the partitioning of motile bacteria in an aqueous two-phase mixture of dextran (DEX) and polyethylene glycol (PEG), which can phase separate into DEX-rich and PEG-rich phases. While non-motile bacteria partition exclusively into the DEX-rich phase in all conditions tested, we observed that motile bacteria penetrate the soft DEX/PEG interface and partition variably among the two phases. For our model organism Bacillus subtilis, the fraction of motile bacteria in the DEX-rich phase increased from 0.58 to 1 as we increased DEX composition within the two-phase region. We hypothesized that the chemical affinity between DEX and the bacteria cell wall acts to weakly confine the bacteria within the DEX-rich phase; however, motility can generate sufficient mechanical forces to overcome the soft confinement and propel the bacteria into the PEG-rich phase. Using optical tweezers to drag a bacterium across the DEX/PEG interface, we demonstrate that the overall bacteria partitioning is determined by a competition between the interfacial forces and bacterial propulsive forces. Our measurements are supported by a theoretical model of dilute active rods embedded within a periodic soft confinement potential.