Insights into the efficient degradation mechanism of extracellular proteases mediated by Purpureocillium lilacinum.

ABSTRACT

Protease secretion is crucial for degrading nematode cuticles using nematophagous fungus Purpureocillium lilacinum, but the secretion pattern of protease remains poorly understood. This study aimed to explore the degradation mechanism of proteases by investigating the characteristics of protease secretion under various carbon and nitrogen sources, and different carbon to nitrogen (CN) ratios in P. lilacinum. The results showed that corn flour as a carbon source and yeast extract as a nitrogen source specifically induced protease secretion in P. lilacinum. P. lilacinum produced significant amounts of gelatinase and casein enzyme at CN ratios of 101, 201, and 401, indicating that higher CN ratios were more beneficial for secreting extracellular proteases. Proteomic analysis revealed 14 proteases, including 4 S8 serine endopeptidases and one M28 aminopeptidase. Among four S8 serine peptidases, Alp1 exhibited a high secretion level at CN ratio less than 51, whereas PR1C, PR1D, and P32 displayed higher secretion levels at higher CN ratios. In addition, the transcription levels of GATA transcription factors were investigated, revealing that Asd-4, A0A179G170, and A0A179HGL4 were more prevalent at a CN ratio of 401. In contrast, the transcription levels of SREP, AreA, and NsdD were higher at lower CN ratios. The putative regulatory profile of extracellular protease production in P. lilacinum, induced by different CN ratios, was analyzed. The findings offered insights into the complexity of protease production and aided in the hydrolytic degradation of nematode cuticles.