Quorum Sensing
When enough bacteria get together (a quorum) they can change their behaviour. They secrete special communication molecules (green), which can diffuse away or be sensed if there is a high enough concentration. This switches on special behaviours like light emission (cyan light), secretion of iron scavengers (blue squiggles, bind iron then turn red), secretion of polysaccharides (orange) and many other types of secretions (purple).
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