Who do you think controls the world? Is it Homo sapiens? Well, breaking news, it’s the microorganisms that control everything. Microbes are omnipresent. They are around us, in the water we drink, the food we eat, on the floor we walk, on our skin, and most importantly they are within us. We can precisely say that it’s not our genetic material but microbes that define us.

We humans have evolved, built civilization upon civilization, invented different languages for communication and networking, and created a society where we live in harmony. Not just humans, but every organism has its own way of communication. Microorganisms have been effortlessly doing it for eons.

Do you think bacteria can take on the world as lone warriors? Well, the answer is no. Group work and communication make them the strongest and this is achieved by a mechanism called Quorum sensing. Let’s understand more about the mechanism of quorum sensing.

Quorum sensing is the process of cell-cell communication between bacteria, and it involves the production, detection, and response to autoinducers. Autoinducers are small chemical signaling molecules that bacteria secrete into their environment and their concentration is monitored by bacteria to track changes in cell number and alter gene expression.

Quorum sensing is carried out majorly by four steps:

1. Bacterial synthesis of small chemical signaling molecules called autoinducers
2. Release of autoinducers into the environment by an either active or passive mechanism
3. Recognition of autoinducers by specific receptors when the concentration exceeds a threshold
4. Altering the gene expression

How does Quorum sensing work?

Bacteria, when alone, divide and secrete autoinducers. These autoinducers, during low cell density, are diffused into the environment. As the bacteria continue to divide it secretes more autoinducers and when the concentration of the signal molecule reaches the threshold, the regulation of the signaling pathway, gene expression, and protein synthesis occur in response to the surrounding cell population. Also, there is an exponential increase in the regulation of proteins secreting autoinducers.

Why is Quorum sensing a crucial mechanism in most bacteria?

That is because quorum sensing aids the organism in achieving different processes like bioluminescence, sporulation, secretion of virulence factor, conjugation, competence, and biofilm formation.

There are three major classes of quorum-sensing systems in bacteria. They are:

1.  LuxI/LuxR–type quorum sensing in Gram-negative bacteria – uses acyl-homoserine lactones (AHL) as signal molecules
2. Oligopeptide-two-component-type quorum sensing in Gram-positive bacteria – uses small peptides as signal molecules
3. luxS-encoded autoinducer- 2 (AI-2) quorum sensing in both Gram-negative and Gram-positive bacteria

We, human beings are capable of communicating only within the species. We cannot understand and communicate with other species. Likewise, can one type of bacterial species communicate with other bacterial species? Or is the mechanism of communicating via quorum sensing limited within species? Let us know more about what the bacteria is capable of with its superpower ‘Quorum sensing’.

Quorum sensing can be either intraspecies or interspecies. Intraspecies quorum sensing enables communication and response within species. Interspecies quorum sensing communicates between different species of bacteria, and it can lead to both collaboration and antagonism between the species. Unfortunately, interspecies quorum sensing is not beneficial most of the time, as some bacterial species collaborate with each other to enhance their virulence factor and create pathogenic biofilms which are resistant to antibiotics.

Human understanding of the tiny world of microorganisms is just the tip of the iceberg. There is an extensively smart communication and networking system between microorganisms. And, we have a long way to go before we understand the language of bacterial communication “Quorum sensing”.

Authored by Nandini, BITS Biocon Certificate Program in Applied Industrial Microbiology, Batch 9

Reference:

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