Abstract
BACKGROUND: Autophagy is used for degradation of cellular components and nutrient recycling. Atg8 is one of the core proteins in autophagy and used as a marker for autophagic detection. However, the autophagy of filamentous fungi is poorly understood compared with that of Saccharomyces cerevisiae. Our previous study revealed that disruption of the autophagy related gene Acatg1 significantly enhanced cephalosporin C yield through reducing degradation of cephalosporin biosynthetic proteins in Acremonium chrysogenum, suggesting that modulation of autophagic process is one promising way to increase antibiotic production in A. chrysogenum. RESULTS: In this study, a S. cerevisiae ATG8 homologue gene Acatg8 was identified from A. chrysogenum. Acatg8 could complement the ATG8 mutation in S. cerevisiae, indicating that Acatg8 is a functional homologue of ATG8. Microscope observation demonstrated the fluorescently labeled AcAtg8 was localized in the cytoplasm and autophagosome of A. chrysogenum, and the expression of Acatg8 was induced by nutrient starvation. Gene disruption and genetic complementation revealed that Acatg8 is essential for autophagosome formation. Disruption of Acatg8 significantly reduced fungal conidiation and delayed conidial germination. Localization of GFP-AcAtg8 implied that autophagy is involved in the early phase of conidial germination. Similar to Acatg1, disruption of Acatg8 remarkably enhanced cephalosporin C yield. The cephalosporin C biosynthetic enzymes (isopenicillin N synthase PcbC and isopenicillin N epimerase CefD2) and peroxisomes were accumulated in the Acatg8 disruption mutant (∆Acatg8), which might be the main reasons for the enhancement of cephalosporin C production. However, the biomass of ΔAcatg8 decreased drastically at the late stage of fermentation, suggesting that autophagy is critical for A. chrysogenum cell survival under nutrition deprived condition. Disruption of Acatg8 also resulted in accumulation of mitochondria, which might produce more reactive oxygen species (ROS) which promotes fungal death. However, the premature death is unfavorable for cephalosporin C production. To solve this problem, a plasmid containing Acatg8 under control of the xylose/xylan-inducible promoter was introduced into ∆Acatg8. Conidiation and growth of the recombinant strain restored to the wild-type level in the medium supplemented with xylose, while the cephalosporin C production maintained at a high level even prolonged fermentation. CONCLUSIONS: Our results demonstrated inducible expression of Acatg8 and disruption of Acatg8 remarkably increased cephalosporin C production. This study provides a promising approach for yield improvement of cephalosporin C in A. chrysogenum.