More detailed investigation of Streptococcus pneumoniae and other gram-positive bacteria, including Bacillus, shows that they develop natural competence in dense cultures. Competence is induced by competence pheromones. (A pheromone is a hormone that travels between organisms, rather than circulating within the same organism). Competence pheromones are short peptides that are secreted into the culture medium by dividing bacteria (Fig. 18.06). Only when the density of bacteria is high will the pheromones reach sufficient levels to trigger competence. This mechanism is presumably meant to ensure that any DNA taken up will come from related bacteria as competence is only induced when there are many nearby cells of the same species.
pheromone Hormone or messenger molecule that travels between organisms, rather than circulating within the same organism
Shorter peptide is cut out = pheromone
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