A microfluidic platform reveals the role of liquid movement on the dispersal of Pseudomonas putida via Pythium ultimum hyphal highways

Abstract Hyphal networks contribute to the connectivity between discrete soil microbial populations by providing a physical network through unsaturated soil matrixes. This network serves as a scaffold for bacteria to disperse and access previously isolated spaces via the “fungal highway”. As bacteria require a liquid film for flagellar swimming, liquid saturation is a significant limiting factor for their dispersal in soil. The current working hypothesis is that bacteria can utilise thin liquid films associated with fungal or fungal-like hyphae to cross air gaps in soil environments. Studying these interactions at the microbial scale, however, is challenging due to the complex and stochastic “black box” nature of soil environments. Hence, the microfluidic Hyphal Highways Device was developed to accomplish long-term quantification of bacterial dispersal along hyphal networks at single-cell level. Key findings highlight that Pythium ultimum is essential for Pseudomonas putida movement across an unsaturated environment, with mycelial biomass and liquid transport being key factors influencing bacterial dispersal. Additionally, P. putida actively modified the distribution of the transported liquid, increasing liquid patch connectivity. The Hyphal Highways Device provided quantitative insights into hyphal-mediated bacterial dispersal, opening new opportunities to study microscale interactions that shape microbial dynamics in natural and agricultural soils.