Natural soils are host to a high density¹ and diversity² of microorganisms, and even deep-earth porous rocks provide a habitat for active microbial communities³. In these environments, microbial transport by disordered flows is relevant for a broad range of natural and engineered processes, from biochemical cycling to remineralization and bioremediation^4,5,6,7. Yet, how bacteria are transported and distributed in the subsurface as a result of the disordered flow and the associated chemical gradients characteristic of porous media has remained poorly understood, in part because studies have so far focused on steady, macroscale chemical gradients^8,9,10. Here, we use a microfluidic model system that captures flow disorder and chemical gradients at the pore scale to quantify the transport and dispersion of the soil-dwelling bacterium Bacillus subtilis in porous media. We observe that chemotaxis strongly modulates the persistence of bacteria in low-flow regions of the pore space, resulting in a 100% increase in their dispersion coefficient. This effect stems directly from the strong pore-scale gradients created by flow disorder and demonstrates that the microscale interplay between bacterial behaviour and pore-scale disorder can impact the macroscale dynamics of biota in the subsurface.

天然土壤是微生物的高密度¹和多样性²的宿主，甚至深层多孔岩石也为活跃的微生物群落³提供了栖息地。在这些环境中，通过无序流动的微生物运输与自然和工程化过程的广泛范围相关，从生化循环到再矿化和生物修复^4,5,6,7。然而，由于水流紊乱以及多孔介质的相关化学梯度特性，细菌如何在地下运输和分布仍知之甚少，部分原因是迄今为止，研究主要集中在稳定的宏观化学梯度[ ^{8,9]， 10}。在这里，我们使用一种微流体模型系统，该系统捕获了孔尺度上的流动紊乱和化学梯度，以量化土壤细菌枯草芽孢杆菌在多孔介质中的运输和分散。我们观察到趋化作用强烈地调节了细菌在孔空间低流量区域中的持久性，导致其分散系数提高了100％。这种效应直接源于流动紊乱产生的强大的孔尺度梯度，表明细菌行为和孔尺度紊乱之间的微观相互作用可影响地下生物群的宏观动力学。