Microbe Communication, Quorum Sensing Behavior, Spreading Resistance, Altruism and More

A previous post shows microbes communicating well enough to form structures and function as a multicellular creature.  Many microbes demonstrate an elaborate language of signals which elicit a wide range of other behaviors.

Messages between microbes often take the form of secreted chemicals. One chemical message tells others that there is not much food in a particular location; those who “hear” it go in other directions.

Individual microbes send out signals that communicate their presence, and when a certain number have signaled they launch various group activities. This is called “quorum sensing.” For example, some colonies of bacteria light up when enough bacteria are present. Similarly, they defend each other from antibiotics, grow food together, and eat each other’s waste.

Attacking a host

Stunningly, another group activity is attacking a host animal.  Individual signals sent out compute the colony’s numbers. This way, they know they’re stronger than their victim’s defense system. When a critical number is reached, they launch an attack. The attack can take many different forms.

In one important example, some microbes stay dormant in the lungs.  When enough gather, and when they sense weaknesses in their victim’s defense system (such as in cystic fibrosis), with a signal the bacteria suddenly stick together and form a hard-to-remove film.  The biofilm waits for the immune system to send blood cells, and when it senses the presence of these cells it launches a new attack with a specific chemical to kill the blood cells.  All the cells do this together on a signal.


When a microbe has become resistant to an antibiotic it releases a signal that aids other stressed members of the colony that are not yet resistant. Interestingly, sending this signal costs the already more successful bacterium by wasting personal resources. The already resistant bacterium constantly manufactures a chemical, indole, which stimulates cellular pumps that allow fellow bacteria to rid themselves of the antibiotics endangering them.  This constant production of indole helps the entire colony become resistant, but damages the producer of the indole. It is damaged in the process of helping others. This is just one version of altruistic behavior in microbes.  Another type of microbe altruism is the formation of the stalk in the social amoeba noted in a previous post.

 Microbe Espionage

Microbes are usually in constant communication with other microbes inside or outside their colony.  But they also intercept communication from other microbes and larger creatures. After interception, the microbe can change its behavior  to defeat the larger creature or to help a comrade. Microbes can interpret the signals of other species and then send return signals to change the other organisms’ behavior.

One microbe sends signals to trick a rival into lowering its defenses. The signal stops  a yeast cell from growing into a more powerful multicellular fungus organism.  In humans, some microbes increase the tendency of children to touch their mouths and thereby aid transmission of the microbe.

In a similar manner, human cells send signals to the bacteria and intercept their communications.  A well-known example is the use of yogurt and other probiotics to send helpful signals in the human gut.  Natural probiotics are colonies of microbes living in the gut that help the cells to maintain normal function and avoid infections.

 Multi-Cultural Cellular Society

These incredibly complex communications occur all the time, as countless colonies of bacteria live in and around us.  In fact, while humans have perhaps 10 trillion of their own cells, they also have ten to a hundred times more bacterial cells and a thousand times more virus cells at any given time.  The vast intercellular communication determines much of what happens in us.

Microbes demonstrate the cognitive abilities of decision-making, group communication, and group behavior. What are the implications of this incredible chatter between microbes and other organisms?