Quorum sensing enables microorganisms to communicate effectively. This coordinates behavior among bacterial communities. In quorum sensing, microbes function as a unified group instead of individuals.
Bacteria can communicate, coordinate and organize into complex, communities with multiple cells. Quorum sensing is how bacteria sense the density of their population through signaling molecules, or autoinducers.
As bacterial populations grow, they release the autoinducers, causing a rise in concentration. When concentration hits a certain threshold, it sparks a coordinated response among the bacteria.
Collective behavior enables several bacterial functions, including biofilm formation, virulence and bioluminescence. Each bacterial species produces its own type of autoinducer.
Gram-negative bacteria often rely on acyl-homoserine lactones as autoinducers. Gram-positive bacteria use peptide-based signals.
When the concentration of this molecule reaches a certain threshold, a "quorum" is achieved. This threshold triggers a change in gene expression in the bacteria, prompting cooperative action by the entire colony.
Biofilm Formation
Biofilms are communities of bacteria or fungi like yeast. They use organic matter, their own bodies and the gluey secretion EPS. This helps them cultivate a favorable environment, often with several microbial species.
Biofilms are found on surfaces like medical implants, pipes, decomposing organic materials or teeth, as plaque. Once enough bacteria attach to a surface, they release signals to trigger production of the protective matrix.
The signals recruit other bacteria, and coordinate the biofilm's growth and development. Biofilms occur throughout the natural world.
A common biofilm maker is Staphylococcus aureus. Biofilms can make S. aureus up to 1000x more resistant to antibiotics than their free-floating relatives.
Virulence in Pathogenic Bacteria
For disease-causing bacteria quorum sensing is a deciding factor in whether they launch an attack. Pseudomonas aeruginosa is best known for causing hospital-acquired infections.
The bacteria use quorum sensing to coordinate the expression of virulence factors, like toxins and enzymes to damage host tissues. Only when they reach a sufficient population size can they overwhelm the immune system.
Quorum sensing mechanisms are present in other microorganisms like fungi and even some eukaryotic cells. It's present not only in virulent microbial activity but in beneficial organisms like digestive bacteria.
In the GI tract quorum sensing helps maintain the balance of microbial communities. It encourages bacteria like Lactobacillus and Enterococcus to colonize and reproduce.
Bioluminescence
Bioluminescence in marine bacteria like Photobacterium phosphoreum, occurs when its population density reaches a tipping point. The bioluminescence is meant to attract prey or deter predators.
Organisms of much study, Vibrio fischeri live in the pineapple fish Monocentris japonicaemi as well as the translucent light organs of several species of squid. If enough cells exist to disguise the squid silhouette from below, the bacteria light up.
Each morning, the squid expels about 90% of A. fischeri in a process of venting. The remaining 10% of bacteria regenerate the population before the next night.
The nocturnal pineapple fish has light-producing organs filled with luminescent bacteria on each side of its lower jaw. Their purpose isn't exactly known. Scientists suspect they may attract prey.
Quorum Quenching is a concept to prevent bacteria from coordinating their virulence or forming biofilms. By interfering with their communication systems, scientists make them more susceptible to traditional antibiotics.
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