MUC5AC and cystic fibrosis: The highest protease activity (4.73 μg azocasein digested per minute per mg of dry biomass) was found in the culture supernatant of the clinical strain grown in the mucin supplemented medium (Fig 1E); this was over two times higher than the activity produced by the environmental strain (Fig 1F), supporting the hypothesis that the clinical strain was thriving in the presence of mucin, which is abundant in the CF lungs [57] by growing well and producing proteases (Fig 1A and 1E).