Growth and protease secretion of ce:italic>Scedosporium aurantiacum/ce:italic> under conditions of hypoxia

摘要

One of the micro-environmental stresses that fungal pathogens, such asScedosporium aurantiacum,colonising human lungs encounterin vivois hypoxia, or deficiency of oxygen. In this work, we studied the impacts of a hypoxic micro-environment (oxygen levels ≤1%) on the growth of a clinicalS. aurantiacumisolate (WM 06.482; CBS 136046) and an environmental strain (S. aurantiacumWM 10.136; CBS 136049) on mucin-containing synthetic cystic fibrosis sputum medium. Additionally, profiles of secreted proteases were compared between the two isolates and protease activity was assessed using class-specific substrates and inhibitors. Overall, both isolates grew slower and produced less biomass under hypoxia compared to normoxic conditions. The pH of the medium decreased to 4.0 over the cultivation time, indicating thatS. aurantiacumreleased acidic compounds into the medium. Accordingly, secreted proteases of the two isolates were dominated by acidic proteases, including aspartic and cysteine proteases, with optimal protease activity at pH 4.0 and 6.0 respectively. The clinical isolate produced higher aspartic and cysteine protease activities. Conversely, all serine proteases, including elastase-like, trypsin-like, chymotrypsin-like and subtilisin-like proteases had higher activities in the environmental isolate. Sequence similarities to 13 secreted proteases were identified by mass spectrometry (MS) by searching against other fungal proteases in the NCBI database. Results from MS analysis were consistent with those from activity assays. The clinical highly-virulent, and environmental low-virulenceS. aurantiacumisolates responded differently to hypoxia in terms of the type of proteases secreted, which may reflect their different virulence properties.