Supervised classification of microbiota mitigates mislabeling errors chemotaxis towards AI-2 should start at lower AI-2 concentrations than uptake and degradation of the signal. Another issue is the extent to which degradation of AI-2 results in a decrease of local AI-2 levels to below the level needed for activation of the motility apparatus. If this mechanism works, it would be interesting to investigate over what distances it is active and under what environmental conditions it is important. In the case of E. coli, this could be the gastrointestinal tract of vertebrates and/or the external environment. Finally, as AI-2 has been reported to regulate the motility of other bacteria such as Campylobacter jejuni and Helicobacter pylori as well (Elvers and Park, 2002; Rader et al., 2007), this active grouping behavior might not be restricted to E. coli and might add yet another dimension to microbial ecology.