Evidence for biosurfactant-induced flow in corners and bacterial spreading in unsaturated porous media. Author Judy Yang, Joseph Sanfilippo, Niki Abbasi, Zemer Gitai, Bonnie Bassler, Howard Stone Publication Year 2021 Type Journal Article Abstract The spread of pathogenic bacteria in unsaturated porous media, where air and liquid coexist in pore spaces, is the major cause of soil contamination by pathogens, soft rot in plants, food spoilage, and many pulmonary diseases. However, visualization and fundamental understanding of bacterial transport in unsaturated porous media are currently lacking, limiting the ability to address the above contamination- and disease-related issues. Here, we demonstrate a previously unreported mechanism by which bacterial cells are transported in unsaturated porous media. We discover that surfactant-producing bacteria can generate flows along corners through surfactant production that changes the wettability of the solid surface. The corner flow velocity is on the order of several millimeters per hour, which is the same order of magnitude as bacterial swarming, one of the fastest known modes of bacterial surface translocation. We successfully predict the critical corner angle for bacterial corner flow to occur based on the biosurfactant-induced change in the contact angle of the bacterial solution on the solid surface. Furthermore, we demonstrate that bacteria can indeed spread by producing biosurfactants in a model soil, which consists of packed angular grains. In addition, we demonstrate that bacterial corner flow is controlled by quorum sensing, the cell-cell communication process that regulates biosurfactant production. Understanding this previously unappreciated bacterial transport mechanism will enable more accurate predictions of bacterial spreading in soil and other unsaturated porous media. Keywords Quorum Sensing, Bacterial Physiological Phenomena, Porosity, Bacteria, Culture Media, Surface-Active Agents, Water, Soil Microbiology, Environmental Pollution, Soil, Wettability Journal Proc Natl Acad Sci U S A Volume 118 Issue 38 Date Published 2021 Sep 21 ISSN Number 1091-6490 DOI 10.1073/pnas.2111060118 Alternate Journal Proc Natl Acad Sci U S A PMCID PMC8463848 PMID 34531326 PubMedPubMed CentralGoogle ScholarBibTeXEndNote X3 XML