A boring world without gender, hormones, or nervous system...

This is an era of universal social interaction. When people meet, they add each other on WeChat and the connection is established immediately. I follow your post and you like mine. We can sense each other's presence and have fun interacting with each other.

In the microbial world, everyone used to sympathize with these poor creatures who couldn’t talk or have emojis. Nobel Prize winner Francois Jacob even described the bacterial world in his 1970 book as “a boring world without gender, hormones, or nervous systems, only individuals that keep reproducing.”

More than 30 years ago, a small animal in the deep sea suddenly became a new favorite of scientists. It is called the Hawaiian bobtail squid, which is only as big as a human finger, but it has a magical ability - its body can glow. After research, scientists found that it is not the squid itself that glows, but the bacteria living in the squid's body that glow.

Vibrio fischeri is a kind of bacteria that coexists with Hawaiian bobtail squids. They live in the light organ in the squid's abdomen, grow with the squid's nutrition, and give back this light-emitting skill, helping the squid to maintain the same brightness as the surrounding environment on moonlit nights, hiding themselves from predators. What's more interesting is that these bacteria do not glow all the time, but only start to glow when the bacteria in the light organ reach a certain concentration.

How do they know that there are enough of them around?

It turns out that each bacterium can release a small amount of signal molecules into the surrounding environment. As the number of bacteria increases, the concentration of signal molecules in the environment gradually increases. When the concentration reaches a certain threshold, specific receptor proteins in the bacteria will bind to it and turn on or inhibit the expression of corresponding genes, thereby allowing all bacteria in the system to complete the same thing in unison, such as the collective luminescence mentioned above. Haha, bacteria can not only communicate, but also do crowdfunding!

The discovery of this ability has once again made humans look at these tiny creatures with new eyes. It was originally thought that only higher animals could perform group behavior, but bacteria can actually do so when they are not well prepared, but once the conditions are ripe, they will raise their arms and receive responses from all directions.

On Thanksgiving Day in 1993, Stephen C. Winans, professor of microbiology at Cornell University, gathered with his family and friends at his home.

Stephen C. Winans was using Agrobacterium tumefaciens as experimental material to study the signal communication ability of bacteria. After trying to understand his brother-in-law's scientific research, his lawyer brother-in-law felt that the bacterial working method of "determining a specific function by the number of groups" was very similar to the rule in human society that requires a quorum to be exceeded when making decisions on some major events. Since then, this ability of bacteria has a formal name - Quorum Sensing (QS).

Gradually, people discovered that many phenomena are related to quorum sensing, such as bacterial accumulation in dental plaque causing periodontal disease, bioluminescence (as shown in Figure 2), spore formation, secretion of toxins during pathogenic bacterial infection, and nitrogen-fixing nodules of rhizobia, etc. Quorum sensing greatly increases the survival probability of microorganisms in the environment and helps bacteria complete their life cycle in an organized and tactical manner.

Take Pseudomonas aeruginosa as an example. It is one of the most unwelcome pathogens in hospitals and often causes infections. The quorum sensing system can not only regulate the secretion of virulence factors of Pseudomonas aeruginosa, but also help Pseudomonas aeruginosa build a bacterial "small castle" with a 3D structure. When they gather in this "small castle" called biofilm, their ability to resist antibiotics and disinfectants will be hundreds or thousands of times higher than that of their companions acting alone! This is why once these bacteria slip through the net and survive by chance, they will cause more serious infections.

The complexity of microorganisms is far beyond people's imagination. Since they can communicate with the help of quorum sensing, they must have the "language" needed for communication. The so-called language is actually the signal molecules they secrete.

At present, it is known that there are at least three "languages" with completely different structures, and under the same "language", there are many "dialects" according to structural differences such as carbon chain length. In addition, in addition to the three "languages", there are also several small "languages". Some bacteria are even more "glib" and proficient in multiple languages! Microorganisms use this to compete with each other and exclude dissidents. For example, Staphylococcus aureus can speak four "dialects". If the faction that speaks a specific "dialect" has an advantage in "number", it will suppress other factions and prevent them from expressing virulence factors. Haha, does it feel like the majority is bullying the minority?

Some of the physiological behaviors regulated by quorum sensing are beneficial, but many pathogens can also use this to endanger the health of humans, animals and plants. In the past, we mainly used antibiotics to deal with pathogens. Now that we have mastered the "language" of some microorganisms, the time is ripe to use quorum sensing to fight back. Researchers use methods such as destroying and interfering with bacterial signal molecules (quorum quenching) to turn microorganisms into "deaf" and "dumb" people who lose their hearing and cannot speak, thereby destroying the quorum sensing network. At present, some companies are engaged in the research and development of quorum sensing disrupting drugs.

Perhaps, in the near future, people will no longer have to worry about the abuse of antibiotics, but can protect human and crop health and promote agricultural production in a calm, non-killing, and only disruptive way. How harmonious that would be!

*This article was first published by "The Fat Devil's Microbial Front" (WeChat ID: nldxhjwswx). Any media reprinting must retain the name and WeChat ID of "The Fat Devil's Microbial Front". Any changes, including the title, are strictly prohibited without permission.

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