Bacteria are tiny unicellular organisms that are everywhere. All the surfaces, waters and crevices are filled with bacteria. They occupy almost every niche on Earth, from the bottom of the oceans, where they survive under tremendous pressure and temperatures up to 121oC [1], to the clouds in the sky [2]. Since their discovery by Antony van Leeuwenhoek in 1676, bacteria were viewed as organisms that lead a predominantly loner lifestyle. In 1988, James A. Shapiro published a fascinating paper, where he argued that bacteria cooperate to form multi-cellular colonies where they behave like multicellular organisms [3]. Furthermore, more landmark studies began to appear, demonstrating that bacteria have evolved sophisticated communication systems, to coordinate the function of the group.
A body of seminal publications (reviewed in [4]), described how Vibrio fischeri bacteria that live inside the bobtail squid, Euprymna scolopes, communicate with each other to produce light. This mechanism is exploited by the bobtail squid to evade predators, while it provides a safe home for the bacteria [4], a win-win situation. The notion of bacterial communication gained ground with the pioneering work of Bonnie Bassler, who deciphered the code bacteria use to communicate with each other [5-9]. Now, it is evident that bacterial communication is ubiquitous and it plays significant role during infection[10]. Thus, finding ways to disrupt this communication, could lead to important therapeutic applications [10, 11].
Bacteria love to attach on surfaces and form large communities, called biofilms [12]. Biofilms are composed of billions of bacterial cells that form continuous mats [12]. Biofilms might look beautiful, when they grow on Petri dishes and form elaborate colourful structures, but can also be lethal, when they develop on medical catheters, or inside our organism [13-15].
A biofilm is a higher-order organised unit (a meta-entity), compared to the single cells it is composed of, and as such, it displays emergent properties. Many of these properties resemble strongly features we find inmulticellular organisms [3, 12].
We know for many years that bacteria contain all the necessary equipment to communicate using electric signals [16]. Actually, intense research of these components, helped us to understand how our nervous system works [16]. The research group of Professor Gürol M. Süel at the University of California San Diego, have revealed, in a beautiful study, that bacteria use these components to communicate with each other in a biofilm [17]. This study was inspired by the observation that bacterial cells, communicate variations in the availability of nutrients across the biofilm, in order to adjust the metabolism of the whole group and share resources more efficiently [18].
The authors discovered that cells of Bacillus subtilis, concentrate potassium ions in their cytoplasm, which they release when nutrients (glutamate) become limited. The generated electrical wave (caused by the release of charged potassium ions), is propagated from the centre of the biofilm to the periphery. This signal communicates to the cells at the periphery of the colony to limit nutrient uptake, so there will be enough remaining to reach the cells at the centre of the biofilm. This mechanism has parallels with the activity of neurones in our brains [19] and provides clues about the functional principles of the mechanisms of cell communication.
These and many more [3, 12] observations should persuade us that we must depart for good, from the idea that bacteria are the ultimate loners. On the contrary, it is evident that they are geared towards intense interaction, with their own and other species. In the laboratory we usually grow bacteria in a flask, with shaking, so they remain planktonic. This situation is unrealistic and never occurs in nature, where bacteria attach on surfaces, they have limited space to move and they have to survive environmental pressures, immune system surveillance, competition and predation from other species of bacteria, eukaryotic protists and viruses [20]. Communication and collaboration are the key elements that help them achieve these feats.Figure 1. Bacteria exist in various forms. When they are free to move in a liquid medium, they are characterised as planktonic. However, when they find the right conditions, they can attach on solid surfaces, multiply and build a biofilm that protects the cells and allows them to collaborate efficiently.
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