Scedosporium are usually soil saprophytes. Among the ten species recognized within the genus, three have been regularly reported as causing human infections, particularly in patients with cystic fibrosis (CF): Scedosporium apiospermum, Scedosporium aurantiacum and Scedosporium boydii. Because of their resistance or low sensitivity to almost all available antifungal drugs, a better understanding of the pathogenic mechanisms of these fungi is required in order to identify news therapeutic targets and to develop new antifungal drugs. Likewise, identification of the origin of the contamination of CF patients may be helpful to propose prophylactic measures. In this aim, environmental studies were conducted on the ecology of these opportunistic molds. Scedosporium species are abundant in human-made environments and have been associated with nutrient-rich substrates, in relation with specific traits of the fungi: ability to survive at low oxygen pressure, to tolerate high salt concentration and to degrade hydrocarbons. Nevertheless, the natural habitat of these fungi is still unknown.

Recent studies have demonstrated the correlation between the lignocellulolytic properties of filamentous fungi and their ability to degrade environmental organic pollutants such as aromatic hydrocarbons. The particular properties of lignin among the lignocellulosic compounds make it an interesting study model molecule. In this context, we attempted to study the adaptive mechanisms developed by Scedosporium species in polluted environments, and hypothesized the involvement of the lignin degradation pathway. 

First, the lignolytic properties of Scedosporium species were confirmed by cultural methods. Indeed, experiments performed in our laboratory highlighted the Scedosporium capacity to grow on agar media containing the different components of lignocellulose as carbon source. A literature search was then performed in order to identify enzymes involved in lignin degradation in other fungi and conserved sequences, which were then used to screen Scedosporium genomic data by tBLASTn (Basic Local Alignment Search Tool) searches. Fifteen candidates were identified, four encoding enzymes of the peroxidase family (conserved domain: Pfam00141) and the others belonging to the oxidase family (conserved domains: Pfam00394/Pfam07731/Pfam07732). Real-Time PCR experiments were then conducted to analyze the relative expression of these genes in presence of the different lignocellulose components and the aromatic compound 4-hydroxybenzoic acid. All peroxidase and an oxidase genes were over-expressed in media containing lignocellulose components (between two to fifteen fold), and similar results were obtained in the presence of 4-hydroxybenzoic acid, suggesting the involvement of the corresponding enzymes in the adaptation to polluted environments. 

Further investigations will be performed to characterize this degradation pathway and to demonstrate its involvement in the adaptation of Scedosporium to the human host.

4 / Lignin degradation pathway in Scedosporium species