Introduction As illustrated by many articles in this special issue, the diversity of mechanisms bacteria use to communicate with one another is remarkable. Quorum sensing is widespread among different bacterial species, emphasizing the importance of coordinating behavior as a group. 1 2 Vibrio harveyi 3 4 Are certain signals better suited for signaling in different types of environments? What are the important parameters influencing signaling in different environments? Pseudomonas aeruginosa 5 7 Staphylococcus aureus Factors affecting signal diffusion, stability, and distribution 1 signal-production rate; the degradation rate or half-life of the signal; the diffusion properties of the signal; and the external hydrodynamic or mass-transfer conditions. The prevailing environmental conditions and resident biology are, to different degrees, important for each of these processes. The effects of signal and environmental chemistry on quorum sensing 8 10 S 11 13 14 15 7 − 14 1 P. aeruginosa 2 16 P. aeruginosa Fig. 1 Predicted AHL half-lives in different alkaline environments  Fig. 2 L. lactis Bu Ha Hb  17 Streptococcus mutans 18 19 cis Rhizobium leguminosarum 19 20 P. aeruginosa 2 21 P. aeruginosa 22 23 P. aeruginosa 24 P. aeruginosa 25 26 27 31 26 luxS Vibrio harveyi 8 S 32 33 34 Salmonella typhimurium R S V. harveyi 2 35 S. typhimurium harveyi 35 harveyi 35 2 Streptococcus pneumoniae 36 Bacillus subtilis 37 38 39 Lactococcus lactis 2 L. lactis 40 Staphylococcus aureus 41 Enterococcus faecalis 42 Listeria monocytogenes 43 44 45 46 47 48 L. lactis S. aureus 49 The effect of the hydrodynamic environment on quorum sensing Mass transfer is the physical process by which molecules are transported in a system, and it has the potential to affect cell-to-cell signaling in many ways. Delivery of nutrients to the active biomass in the structured community is one example. This could affect the relative metabolic activity of the community, which in turn has the potential to affect signal-production rates. Mass transfer is affected by the hydrodynamics of the bulk fluid and the geometry of the structured community. These two factors affect each other, because a microbial community both shapes, and is shaped by, its external environment. 3 δ δ δ \documentclass[12pt]{minimal}
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