PCTP and cystic fibrosis: Although physiological significance of the PctP-mediated chemotactic response of P. aeruginosa to guanine and other purine derivatives remains to be elucidated, P. aeruginosa infection might be limited by low availability of nucleobases in the human host (65), including the growth of P. aeruginosa in the lungs of cystic fibrosis (CF) patients (66).