Peptone source effects on recombinant protease production and cellular responses in yeast

The production of recombinant protease is critical due to their wide range of industrial applications. This study investigates the impact of the peptone switching in the fermentation media on recombinant protease production and cell metabolism. The yeast Saccharomyces cerevisiae was used as the expression host, comparing growth and protease activity in YPD medium (containing bacteriological peptone) and a modified version, YTD medium (containing tryptone). Switching from bacteriological peptone to tryptone resulted in a 35.22% increase in cell density for the protease-producing strain B_lasB2, although protease activity remained undetectable. Peptone switching also resulted in a noticeable shift in broth color from pale yellow to brownish yellow, which was reversed upon deletion of the FET3 gene, a homolog of mushroom tyrosinase, and its complex FTR1. Western blot analysis confirmed that the protease was synthesized but remained in an inactive form. RNA sequencing revealed substantial shifts in transcriptional profiles in response to peptone switching. In YTD medium, there was a predominant upregulation of genes involved in protein folding, primarily located in the endoplasmic reticulum lumen. Conversely, in YPD medium, significant downregulation occurred, affecting genes involved in mitochondrial translation and located within the mitochondria. These findings highlight that peptone switching not only affects cell growth and enzyme activity but also induces significant changes in the yeast’s transcriptional landscape. This study provides deeper insights into the metabolic adjustments that yeast undergoes in different fermentation conditions and underscores the complex relationship between peptone source, protease production, and protease activity.