Interestingly, many, if not most, bacterial cells can communicate with other cells in the same species. The bacteria secrete proteins, and, once enough bacteria are present, the concentration of the proteins increases. A high concentration often triggers the bacteria to turn on other proteins so the colony can perform a function. For example, individuals who have impaired immune systems or who have the genetic disease cystic fibrosis (CF) are often infected by the respiratory bacterium, Pseudomonas aeruginosa. Only when enough bacteria have accumulated, P. aeruginosa will produce an enzyme that degrades lung tissue which allows the bacteria to invade the blood stream.
Although many examples of this intraspecies communication exist, scientists wondered if different species can communicate with each other. To answer this question, researchers examined the relationship between P. aeruginosa and Burkholderiacepacia. B. cepacia causes fatal lung infections in CF patients, but only after these individuals have also been infected by P. aeruginosa.
P. aeruginosa were grown in an appropriate liquid medium in the laboratory. The culture was centrifuged to remove the bacterial cells. A culture of B. cepacia was then grown in the medium. These bacteria increased production of molecules necessary for survival.
Mutant P. aeruginosa were grown in the laboratory in liquid medium. After centrifugation, the medium was used to incubate cultures of B. cepacia. Very few “survival molecules” were produced in the B. cepacia.
The mutant P. aeruginosa used in Experiment 2 were most likely deficient in:
The most likely answer to this question is that the P. aeruginosa were defective in secretion. If they had mutations in any other system, they would be unlikely to survive and reproduce.