Читать книгу Astrobiology - Charles S. Cockell - Страница 128

Multicellular eukaryotes communicate with a large array of methods from making noises to body movements. They are interpreted by other organisms through touch, eyesight, and hearing. However, prokaryotes also communicate. Known as quorum sensing, this allows microbes to sense whether other microbes are close to them, and to regulate their chemical processes accordingly.

Quorum sensing was first discovered in the microbe Vibrio fischeri that colonizes the light-producing organs of some fish and squid, where the microbes are responsible for producing the light through bioluminescence. When the V. fischeri microbes are in normal seawater, where they rarely come into contact with another member of the same species, they do not produce any light. However, once they reach a high concentration, such as inside the squid's light-producing organ, they sense the presence of others, and the light-producing chemical reactions are triggered.

Why would microbes sense other microbes? Quorum sensing provides microbes with a means to sense how much competition there might be for resources and to regulate their activity accordingly. In some ways, it is a type of cooperation, but it also benefits each individual microbe to sense whether it is alone or not. For example, if there is intense competition for resources, it might be better to use less energy and become more inactive. An example is to be found in the microbe P. aeruginosa, which can live as individual cells, but at a certain concentration of cells, they form a structured biofilm which can allow them to be more resistant to environmental extremes. Quorum sensing is mediated by organic molecules such as very small chains of amino acids (peptides). The prokaryotic ability to engage in rudimentary forms of communication shows us that interactions between cells and complex social dynamics are not just the preserve of multicelled eukaryotes, but communication can also modify and shape prokaryotic populations.