This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Microorganisms regulate key processes in soils and aquifers, including nutrient cycling, carbon turnover and contaminant degradation. Many bacteria use chemotaxis, the ability to sense and swim toward chemical signals, to locate nutrient-rich hotspots.
However, natural subsurface environments are highly heterogeneous, containing complex pore networks that create strong variations in fluid flow and nutrient availability. How these physical conditions influence bacterial foraging has remained poorly understood. The research group led by Joaquín Jiménez-Martínez, professor of subsurface environmental processes at ETH Zurich and Eawag, developed a novel microfluidic platform in collaboration with professor Roman Stocker of ETH Zurich and researchers from the Spanish Institute of Environmental Assessment and Water Research (IDAEA-CSIC).
The platform reproduces realistic subsurface conditions while allowing direct observation of individual bacterial cells. The system creates controlled nutrient hotspots that mimic those found around soil aggregates, organic matter, contaminants or plant roots. Using this platform, the team tracked the movements of single cells of the soil bacterium Azospirillum brasilense under different flow conditions and pore-space structures.
The study, published in the Proceedings of the National Academy of Sciences, revealed that physical heterogeneity enhances the benefits of bacterial motility and chemotaxis. Contrary to the common assumption that fluid flow suppresses bacterial navigation, the researchers found that complex porous structures create low-velocity regions where bacteria can remain longer and swim effectively toward nutrient sources. As a result, chemotactic bacteria experienced substantially greater nutrient exposure than nonmotile cells transported passively by the flow.
The advantage of chemotaxis increased by about 1.5-fold in highly heterogeneous porous media compared with uniform flow environments. The researchers also showed that pore-scale heterogeneity allows chemotaxis to remain advantageous across a broader range of flow velocities. In porous media, local flow variations enable bacteria to continue accessing nutrient hotspots even under conditions where chemotaxis becomes ineffective in homogeneous environments.
These findings demonstrate that microscale physical heterogeneity is a key factor shaping microbial behavior in the subsurface and provide new insights for understanding soil respiration, nutrient cycling, groundwater remediation and environmental management. Stoll et al, Porous medium heterogeneity favors chemotaxis to nutrient hotspots in flow, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2616336123 Journal information: Proceedings of the National Academy of Sciences BA art history, MA material culture.
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