Chemotaxis as a navigation strategy to boost range expansion

Abstract

Bacterial chemotaxis, the directed movement of cells along "chemoattractant" gradients, is among the best-characterized subjects of molecular biology 1-10. Much less is known about its physiological roles 11. Commonly, it is seen as starvation response when nutrients run out, or as escape response from harmful situations 12-16. Here, we establish an alternative role of chemotaxis by systematically examining the spatiotemporal dynamics of Escherichia coli in soft agar 12,17,18 : Chemotaxis in nutrient-replete conditions promotes the expansion of bacterial populations into unoccupied territories well before nutrients run out in the current environment. We show how low levels of chemoattractants act as aroma-like cues in this process, establishing the direction and enhancing the speed of population movement along the self-generated attractant gradients. This navigated range expansion process spreads faster and yields larger population gains than unguided expansion following the canonical Fisher-Kolmogorov dynamics 19,20 and is therefore a general strategy to promote population growth in spatially extended, nutrient-replete environments.

Distinct chemotactic behavior in the originalEscherichia coliK-12 depending on forward-and-backward swimming, not on run-tumble movements

“…Taken together, we conclude that swarm ring formation corresponds to flagellar polymorphism and speculate that agar experiments fail to detect the motility of many cells. Our results complement recent, beautiful work on how microorganisms migrate in structured environments [18] and will lead to a discussion of how E. coli cells have adapted for survival through the evolution of flagellar transformation.…”

“…A recent study proposed a mechanism for navigated range expansion in E. coli cells, in a structured environment (semi-solid agar plate). It suggested a population fitness mechanism that recognizes nutrients and chemical gradients, which serve as a local guide and allow rapid expansion into unoccupied territories (outer edge) [18]. However, the reason why the original K-12 strain exhibits no motility remains unclear, and we infer that these non-motile cells have uncharacterized and exciting features to contribute to the field of bacterial flagellar studies.…”

Dissecting the impact of metabolic environment on three common cancer cell phenotypes

“…The phenotype relationships across metabolic environments for the tested cancer cells reported here are remarkably similar to the empirical “growth laws” 46,47 by which nutrient availability governs analogous phenotypes in microbes. For example, slow-growth environments tend to increase antibiotic survival 48,49 and decrease colony expansion rates 50 in bacteria. This resemblance is particularly striking when comparing the patterns of overflow metabolism in cancer cells and microbes: as observed here in cancer cells, the main determinant of microbial overflow metabolism is also not growth rate per se , but rather the type of nutrient limitation cells face in their environment 11,51 .…”

Chemotactic Migration of Bacteria in Porous Media

“…This process can mediate migration of a population of cells when they continually consume a surrounding attractant: the cells collectively generate a local gradient that they in turn bias their motion along, spectacularly leading to the formation of a coherent front of cells that continually propagates (8). This phenomenon can enable populations to escape from harmful environments or to colonize new terrain (9). Thus, chemotactic migration has been extensively investigated under diverse conditions in bulk liquid (7)(8)(9)(10)(11)(12).…”

“…This phenomenon can enable populations to escape from harmful environments or to colonize new terrain (9). Thus, chemotactic migration has been extensively investigated under diverse conditions in bulk liquid (7)(8)(9)(10)(11)(12).…”