Biology

How do bacteria know when there are enough of them?

Bacteria constantly release a small chemical, called a signal molecule, and constantly sense how much of it is in the water around them. A crowded population keeps that amount high. Marine bacteria that make light stay dark until they reach about 100 million cells per millilitre. The mechanism is called quorum sensing.

Sources & further reading

Cold Spring Harbor Perspectives in Medicine (Cold Spring Harbor Laboratory Press), via PMC / NIHBacterial Quorum Sensing: Its Role in Virulence and Possibilities for Its ControlAn open-access review by Bonnie Bassler, the scientist who did most to establish that bacteria talk, covering how the sensing works and why it matters in disease.Journal of Bacteriology (American Society for Microbiology)Cellular control of the synthesis and activity of the bacterial luminescent systemThe 1970 experiment that first spotted the effect: bacteria only start glowing once their own growing crowd has conditioned the water around them.International Journal of Molecular Sciences (MDPI), via PMC / NIHQuorum Sensing in the Squid-Vibrio SymbiosisA review of the partnership between a small Hawaiian squid and the glowing bacteria it farms in a dedicated organ to erase its own shadow.Scientific Reports (Nature Portfolio)Honing in on bioluminescent milky seas from spaceThe satellite study that found a patch of ocean the size of Iceland glowing south of Java, bacteria switching on together because the crowd got big enough.Proceedings of the National Academy of Sciences (National Academy of Sciences)Boat encounter with the 2019 Java bioluminescent milky sea: Views from on-deck confirm satellite detectionThe follow-up report from sailors who actually crossed the glowing sea, confirming what the satellite saw was real.Proceedings of the National Academy of Sciences (National Academy of Sciences)Quorum-sensing regulators control virulence gene expression in Vibrio choleraeThe study showing cholera bacteria turn their attack genes off once there are enough of them, proof that the bacterial vote can go either way.Nature (Nature Publishing Group), via PMC / NIHSynchronized cycles of bacterial lysis for in vivo deliveryAn engineering paper where researchers hijacked the bacterial signal molecule so a colony bursts on cue inside a tumour and releases a drug, over and over.Annual Review of Cell and Developmental Biology (Annual Reviews)Quorum Sensing: Cell-to-Cell Communication in BacteriaThe standard review article that established bacteria communicate as mainstream biology, covering the signal molecules and the behaviours they switch on.