ABSTRACT 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 shear flow promotes growth of the human pathogens Pseudomonas aeruginosa and Vibrio cholerae at surprisingly low nutrient concentrations. In static environments, cells require high nutrient concentrations as they steadily consume non-renewable resources. In slower-flowing environments, cells grow and deplete nutrients, which generates spatial gradient profiles. In faster-flowing environments, cells grow robustly and form microcolonies even at very low concentrations due to rapid nutrient replenishment. 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 shear flow can promote bacterial growth and shape spatial gradients. IMPORTANCE While bacteria in nature experience flow, laboratory conditions typically omit flow. Additionally, bacteria in nature are often nutrient-limited, but laboratory conditions contain excess nutrients. Here, we use microfluidic technology to determine how flow impacts growth of a bacterial pathogen under nutrient limitation. We discover that flow sustains growth at glucose concentrations 1,000 times lower than traditionally observed. In traditional experiments, bacteria grow on a high concentration of a non-renewable resource. In our microfluidic experiments, bacteria can grow on surprisingly low concentrations of resources if they are renewed by flow. Our results emphasize the need to study bacteria in realistic contexts and suggest that scientists should rethink how cells experience nutrient limitation in nature.
Padron et al. (Fri,) studied this question.