ADHESION OF PSEUDOMONAS-AERUGINOSA TO RESPIRATORY MUCINS AND EXPRESSION OF MUCIN-BINDING PROTEINS ARE INCREASED BY LIMITING IRON DURING GROWTH

The attachment of Pseudomonas aeruginosa to human respiratory mucus re presents an important step in the development of lung infection, espec ially in cystic fibrosis. Local factors in the respiratory tract, such as osmolarity or iron concentration, might influence this colonizatio n. In the present work, we have observed that overall levels of adhesi on of two nonmucoid, nonpiliated strains of P. aeruginosa, 1244-NP and PAK-NP, to human airway mucins were higher when these strains were gr own in a minimal medium of low osmolarity (M9) than when they were gro wn in a rich medium of higher osmolarity (tryptic soy broth [TSB]). Ho wever, increasing the NaCl concentration of M9 to increase the osmolar ity did not modify the level of binding. In order to find out whether these differences were due to variations in nutrients, the influence o f iron concentration was investigated: the levels of binding of the tw o strains increased after TSB was depleted of iron and decreased after iron was added to M9. Since the outer membranes from the two strains have been shown to contain proteins reacting with human bronchial muci ns, we compared the mucin-binding proteins expressed by the two strain s grown in different media. When the nonpiliated strains 1244-NP and P AK-NP were grown in the different media, previously observed mucin-bin ding bands were detected in the 42- to 48-kDa range but additional muc in-binding bands in the 77- to 85-kDa range were detected when these s trains were grown in M9 or iron-deprived TSB. These results demonstrat e that the adhesion of P. aeruginosa and the expression of mucin-bindi ng proteins in the outer membranes of nonpiliated P. aeruginosa are af fected by the iron content of the medium in which the bacteria are gro wn and not by the osmolarity.