A bacteria try to make contact or sense with other bacterial cells in order to coordinate with each other, this is called Quorum Sensing. It improves their survival. Many bacteria come together in one particular place which is enough to form a quorum so that the number of members have to vote for a certain issue in a procedure like parliamentary procedure, then they will communicate with each other through chemical messages (called “quorum sensing“). It is a certain arrangement with which every cell can find out what type and (to a certain extent) how many cells are present around it. So many species of bacteria use this procedure of QS to coordinate with other cells according to the quantity of their nearest population.
Single bacterial species(left) diverse bacterial species(right)
Some social insects like ants, bees etc. use quorum sensing to find the suitable place to build their nest. The rock ant found in Europe build their nest in small cracks between big rocks. But sometimes if the rock shifts their position, the ants have to find a new place to build their nests. Similarly, honey bees also use this type of sensing mechanism to make quick decision to build their nests. Now a days quorum sensing is used to get together the certain behavior of the autonomous swarm robotics. Using QS they can decide without knowing the controller direction.
Here is the history of Quorum Sensing:
- Quorum Sensing was first found in marine species, called vibrio fischeri (a rod-shaped bacteria). This lives in symbiotic relationship in the light producing organ of the bobtail squid in Hawaii. Since these cells are living freely, the autoinducer is at low concentration, as a results the cells cannot sense. When they are concentrated in the light-producing organ, transcription of luciferace enzyme is induced, which results to bioluminescence.
FIG:The Hawaiian bobtail squid, its photophores populated with Allivibriofischeri
Quorum Sensing feature is present in most bacterial species, but how the signals are made, detected, and responded differs considerably from species to species. It collectively results in many behaviour.
Few such behaviours are explained below:
At low cell density the autoinducers (red dots) that are produced spread through the cells into the growth media. When the cell growth continues, the level of autoinducers in the media will start to gather in a restricted environment. A very low intensity of light will be detected. High levels of autoinducers will be activate in the luminescent systems of the bacteria in the media. The regulatory response to the autoinducer leading to induction of luxCDABE genes is termed as Quorum Sensing.
Quorum Sensing is a distinctive attribute of most of the bacterial species But they will differ in the implementation of the signals, detection, and response from species to species.
A biofilm is a combined form of microorganisms associated with a surface and enclosed in a polymeric matrix. This can form on both solid and liquid surfaces and may be collection of a single species or many species of microorganism. Biofilm formation starts with combining of microorganisms to a surface by means of weak and reversible associations.If they are not removed, then the microorganisms form even more permanent, irreversible attachments using adhesion structures. The cells forming as monolayer thick will soon grow and divide, before producing an exopolymer matrix to enclose the developing colony. As soon as the biofilm develops, the microorganisms started to alter their gene structure as the result of changes in population density.
This behaviour is called Quorum Sensing and is brought by the release of chemicals from colony cells. Individual cells release inducer chemicals that will trigger specific transcriptional changes when a threshold is surpassed. As cells begin to aggregate, the concentration of inducer chemicals increases to exceed the required threshold.This triggers a synchronised change in gene expression, allowing the biofilm to operate as a coordinated system. QS allows the biofilm to grow and develop and promotes stability of the structure. Channels are formed in order to make easy the spread as well as the incorporation of nutrients throughout the biofilm.
Metabolic activity will make changes in the micro-environment, which augments differential distribution of microorganism, establishing an oxygen gradient that deferentially localise aerobic and anaerobic metabolisers. Through QS, microorganisms in a biofilm tends to create new synergistic effects (emergent properties).
One emergent property commonly identified in biofilms is an increased resistance to antimicrobial agents. Within a biofilm, some microorganisms develop into non-dividing, slow-growing persister cells. These cells exist within a physiologically dormant state, which makes them insensitive to the action of antimicrobial drugs. Consequently, these cells survive antimicrobial treatments and function as a reserve from which the biofilm can repopulate. This renders antimicrobial drugs ineffective in the treatment of biofilms and associated diseases.
Like the old saying, we are more like microbial than human, the small micro level organism out-think the macro level human beings. GREAT THINGS ARE DONE BY A SERIES OF SMALL THINGS BROUGHT TOGETHER.