You evolved this cute little system to measure local cell density involving a small extracellular molecule that all individuals in a population produce and sense. While we higher eukaryotes go around being all greedy and selfish, you figured out a way to communicate and cooperate with your fellow prokaryotes. Don’t look so delighted with yourself. Let me remind you, its just evolution and evolution is easier than revolution. So while the workers of the world unite, you little bacterial fuckers go around coordinating your behavior by producing molecules for the common public good, like Simpsons paradox is not a paradox to you. And to that I say CONJUGATE YOU!
Vibrio fischeri, as the poster bacterium for quorum sensing, you’re number 1 on this shit-list. Your luciferase operon is the paradigm for quorum sensing. The operon that consists of the LuxI gene that produces acyl-homoserine lactone (AHL) that is exported out of the cell. This molecule induces the regulator LuxR that in turn induces the lux operon. You know the operon I’m talking about: luxICDABE. At first glance, this is just an innocent feed forward loop that we all use as on/off switches for cellular functioning. But then you went and made it all fancy by having genes like flavin-dependent monooxygenase luciferase that can catalyze the oxidation of reduced riboflavin and a long-chain aliphatic aldehyde to produce light. Let me point out that you spend all this energy (115 kcal/mol) on reduction to produce the FMNH2 molecule and 2 NADHs which you then oxidize to produce light at 490nm wavelength giving you only 59 kcal/mol. Somehow, this obvious waste of energy does not deter you. And you produce 1000 photons per second per bacterium??? I’ve spent many a ~10 mins in a dark room with you, waiting for my eyes to acclimatize so I may witness your luminous highness. You know what, it ain’t worth it!
I may have even been able to live with your seemingly wasteful production of light if it were just for for an artistic outlet. But we know that you go around recruiting squids and fish (and who knows what else that lurk in the deep dark depths of the ocean) to your little rave parties. I can imagine the conversation now: “What up Euprymna scolopes! It must be hard being a tiny squid with all these predators around. We can help. We can trick your immune system into letting us hang out and luminess in your invaginated epithelial crypts of an organ that you make specifically to house us. It’s for your antipredatory behavior… we can counterilluminate so that you are camouflaged. We get nothing out of this. We’re doing this totally selflessly.” Prokaryotic selfless behavior! Like that happens. And as always, in an attempt to humble your great prokaryotic ego (only paralleled by your sheer number in the world), I would like to draw your attention to other organisms that do the same thing with no help from you. Dinoflagellates, cnidarians, fungi, shrimps and fireflies, to name a few. And some of them, like the dinoflagellates use this super power for cool things with it like to populate the Bioluminescent Bay that we humans can enjoy.
We have only begin to uncover the range of mechanisms you use to regulate this quorum-sensing. There are multiple autoinducer circuits that control different behaviors. They can act in parallel or by competition through phosphorelation and kinase pathways. And just when we thought we eukaryotes were special for having regulatory micro RNAs, we find that you use ‘small regulatory RNAs’ to even more sensitively react to the concentrations of inducers. And so we continue to study you with a deep fear and disgust of what we may find in your chemical vocabulary. I know you think Bonnie Bassler et. al. <3 you and sing the praises of your intricately regulated social interactions. But the truth is, my quorum-sensing light-producing cooperatively-benefiting little conjugating friends, you and your quorum sensing unions are just keeping more brilliant scientists from doing important things like curing cancer. I hope you’re happy.
Oh right. You like cancer. Your Agrobacterium cousins use quorum-sensing to form tumors on plant roots in which they can have huge orgies to exchange DNA. I’m sure that’s a totally selfless relationship as well. Since most of your cousins can produce some version of these AHL communication molecules, there’s the inter-species communications machinery issue. Must I even mention the large conjugating orgies across species and genus boundaries that you can initiate though quorum-sensing? But just when I thought you were just trying to have a free HGT party I find out that you all engage in some strange form of warfare in which you try to intercept communications of other populations. You can secrete enzymes that make AHLs of another species inactive. You produce competing receptors to titrate the AHLs in the environment. Your obvious disregard for your fellow prokaryotes disgusts me. I hope you annihilate yourselves by ensuring mutual communication destruction!
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