In the last part, we covered a important way of how bacteria communicate to each other through quorum sensing . The LuxI-LuxR system describes an interesting signaling system used by bacteria of the same species. Professor Bassler's laboratory is especially known for her work on autoinducer 2 (AI-2) system which allows for inter-species communication. The discovery of AI-2, and its fundamental workings were a true scientific detective stories with twists and turns, and its implications are still being researched today. Work on a different luminescent marine bacterium, Vibrio harveyi , revealed that regulatory apparatus for creating luminescent was more complex. It relied on two separate input signals: AI-1 and AI-2 which were recogized by two membrane spanning receptor kinases LuxQ and LuxN respectively. How AI-1 and AI-2 are involved for luminescence may be less important here except to say that both signals need to be present. While more information could be inferred about AI