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10 páginas.- 4 figuras.- 4 tablas.- 45 referencias.- The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.2c03149, Recent research has demonstrated that chemotactic bacteria can disperse inside microsized pores while traveling toward favorable conditions. Microbe–microbe cotransport might enable nonmotile bacteria to be carried with motile partners to enhance their dispersion and reduce their deposition in porous systems. The aim of this study was to demonstrate the enhancement in the dispersion of nonmotile bacteria (Mycobacterium gilvum VM552, a polycyclic aromatic hydrocarbon-degrader, and Sphingobium sp. D4, a hexachlorocyclohexane-degrader, through micrometer-sized pores near the exclusion-cell-size limit, in the presence of motile Pseudomonas putida G7 cells. For this purpose, we used bioreactors equipped with two chambers that were separated with membrane filters with 3, 5, and 12 μm pore sizes and capillary polydimethylsiloxane (PDMS) microarrays (20 μm × 35 μm × 2.2 mm). The cotransport of nonmotile bacteria occurred exclusively in the presence of a chemoattractant concentration gradient, and therefore, a directed flow of motile cells. This cotransport was more intense in the presence of larger pores (12 μm) and strong chemoeffectors (γ-aminobutyric acid). The mechanism that governed cotransport at the cell scale involved mechanical pushing and hydrodynamic interactions. Chemotaxis-mediated cotransport of bacterial degraders and its implications in pore accessibility opens new avenues for the enhancement of bacterial dispersion in porous media and the biodegradation of heterogeneously contaminated scenarios., This research was funded by European Union's Horizon 2020 research and innovation program under the Marie Sklodowska- Curie grant agreement no. 895340 (BIOTAC project) and by the Spanish Ministry of Science and Innovation (PID2019- 109700RB-C21) .

10 páginas.- 6 figuras.- 1 tabla.- referencias .- . Supplementary data Figures showing the FIB-SEM images of the membrane bioreactor experiments, the tactic response of Pseudomonas putida G7 under sonication conditions in transport assays and capillary test and bioreactor transport experiments with different concentrations of the chemoeffectors. Tables showing the experimental growth control with chemical effectors and bacterial accessibility to the different porous fractions of contaminated soil. Supplementary data to this article can be found online at: doi.org/10.1016/j.scitotenv.2022.154938, A major cause of high bioremediation endpoints is the limited bioaccessibility to residual contaminants resting in soil pores with diameters close to the size exclusion limit of bacterial cells. Under nongrowing conditions and in the absence of hydraulic flow, we examined how the tactic behavior of motile, contaminant-degrading Pseudomonas putida G7 cells (2 × 1 μm) influenced passage through membranes with pores ranging in size from 1 μm to 12 μm. The bacteria were spontaneously retained by the membranes - even those with the largest pore size. However, the cells were mobilized through 5 μm and 12 μm pores after the application of an attractant (salicylate). Mobilization also occurred by attraction to the common root exudate constituents γ-aminobutyric acid and citrate and repellence (or negative taxis) to zero-valent iron nanoparticles. The observed pore size threshold for tactic mobilization (5 μm) and unaltered cell fluxes and effective cell diffusion against different chemoeffector strengths and concentrations suggest that there is a physical constraint on the gradient sensing mechanism at the pores that drives the tactic response. Our results indicate that chemically mediated, small-scale tactic reactions of motile bacteria may become relevant to enhance the bioaccessibility of the residual contaminants present in micrometer-sized soil pores., We would like to thank the Spanish Ministries of Economy and Competitiveness (CGL2016-77497-R) and Science and Innovation (BES-2017-079905 and PID2019-109700RB-C21) for supporting this work