Flow rapidly replenishes scarce nutrients to promote bacterial growth
In laboratory settings, bacteria grow in static culture with more nutrients than they require. However, bacteria in nature experience flowing environments that are nutrient limited. Using microfluidics and single cell imaging, we discover that flow promotes growth of the human pathogen Pseudomonas aeruginosa at surprisingly low nutrient concentrations. In static environments, cells require high nutrient concentrations as they steadily consume non-renewable resources. In flowing environments, cells grow robustly at very low nutrient concentrations that are constantly replenished. Our simulation-guided experiments show how stopping flow halts growth within minutes and varying flow impacts growth gradients across bacterial populations. By precisely delivering nutrients using microfluidics, we learned that cells in flow can grow on glucose concentrations 1,000 times lower than those observed in typical laboratory experiments. The ultralow glucose concentrations sufficient for growth in flow closely align with the affinity of bacterial glucose transporters, suggesting that bacteria have evolved in flowing environments with scarce nutrients. Collectively, our results emphasize the limits of traditional culturing approaches and highlight how depleted environments can unexpectedly support bacterial growth.