How Bacteria Talk To Each Other

Updated 1/29/2016 & 6/26/2016.


Did you know bacteria ‘talk’ with one another? Although bacteria are primitive single-celled organisms, their ability to use chemical signals to communicate with each allows them to synchronize their behavior and act together much like large, multi-cellular organisms. This communication process allows pathogenic bacteria to know when they have amassed enough troops to mount a successful attack to infect a plant or animal, including humans. (Cunningham,  2001-2010) & (iBiology, 2006-2016)
Scientists call this cell to cell signaling signaling process Quorum Sensing. Each bacterium measures the concentration of its fellows by sending out a chemical signal and  ‘listening’ for the chemical signals from other like bacteria.


Pathogenic bacteria use cell signaling to monitor their density and will activate some genes only when they know that their population is large enough to make it safe to begin that activity – ie, when they know there are enough of them who can coordinate to effect changes in cellular behavior, to try to make us sick. (Cunningham,  2001-2010)
Bacteria of the same variety can also coordinate to divide into sub-populations that carry out different activities. “For example, in the late 1990s an investigation of a biofilm community, the marine bacterium Pseudoalteromonas, revealed two physiologically distinct subpopulations. In effect there was a cellular division of labor: one group stayed attached to the surface and made nutrient available to the second group, which reproduced and released daughter cells to the surrounding water.” (Cunningham,  2001-2010)
Not only do bacteria ‘talk’ with their kind, they also have the ability to communicate with other types of bacteria (inter-species communication) – and use different chemical languages for these purposes. Bacteria are apparently multilingual.  (iBiology, 2006-2016)
Pretty impressive for single cell organisms!


Pathogenic Cell-Cell Communication


In the cartoon above, various species of bacteria are represented by different colors. Bacteria can produce chemical signals (“talk”) and other bacteria can respond to them (“listen”) in a process commonly known as cell-cell communication or cell-cell signaling. This communication can result in coordinated behavior of microbial populations. (Courtesy, MSU-CBE.)







Molecular Biologist Bonnie Bassler decoded this Quorum Sensing process in pathogenic bacteria. She explains how they do it in this 2009 TED Talk.
Dr Bassler is a Howard Hughes Medical Institute Investigator and the Squibb Professor of Molecular Biology at Princeton University.




Here’s more of Bonnie Bassler – this time explaining the role of Quorum Sensing communication in the symbiotic relationship between luminescent bacteria (Vibrio fischeri ) and the tiny Hawaiian bobtail squid living off the coast of Hawaii.



The tiny squid’s luminescence comes from colonies of Vibrio fischeri bacteria housed in the squid’s internal light organs. These bacteria secrete a chemical that, when it reaches a sufficient concentration, stimulates the bacteria to glow. How and why they do it is fascinating.



If you’re now really hooked by this topic and want even more, here’s Dr Bassler’s longer video that the short squid-luminescent bacteria video is taken from:  Part 1: Bacterial Communication via Quorum Sensing (53:47 minutes). 








Lest you think you’re doomed to be overrun with pathogenic bacteria plotting against you, the good news is that probiotics interfere with the quorum sensing signalling agents in pathogenic bacteria.
“… The probiotic bacteria such as Lactobacillus, Bifadobacterium and B. cereus strains degrade the auto-inducers of pathogenic bacteria by enzymatic secretion or production of auto-inducer antagonists which render the quorum sensing bacteria mute and deaf.” (Brown, 2016)
Excellent news!



If you find it fascinating that bacteria communicate with other and want more related information, see The Soil’s Microbiome and How Do Plants Communicate with Each Other? for information on how bacteria in the soil and plants communicate with one another.




And see Repair the Soil’s Microbiome to Resolve the Climate Crisis for a brief video by the brilliant and ever sensible Michael Pollan.






Bassler, B. (6/10/2009).  Bacterial Communication. iBiology video. See:

Bassler, B. (2009). Bonnie Bassler (Princeton) Part 1: Bacterial Communication via Quorum Sensing. iBiology video. See:

Brown, M. (2011). Modes of Action of Probiotics: Recent Developments. Journal of Animal and Veterinary Advances, 10:14, 1895-1900. See:

Cunningham, A.B., et al (Eds). (2001-2010). The Biofilms Hypertextbook. Chapter 1: Introduction to Biofilms. See:

Hardin, J.R. (12/23/2013). The Soil’s Microbiome. See:

Hardin, J.R. (3/8/2014). How Do Plants Communicate with Each Other? See:

Hardin, J.R. (1/29/2016). Repair the Soil’s Microbiome to Resolve the Climate Crisis. See:




© Copyright 2016. Joan Rothchild Hardin. All Rights Reserved.

