Optimization of Fermentation and Transcriptomic Analysis of a High-Protein-Producing Galactomyces geotrichum Strain

The global shortage of protein resources drives the need for sustainable microbial protein production. Galactomyces geotrichum can convert various substrates into high-quality single-cell protein (SCP). In this study, a strain of Galactomyces geotrichum (Gg6) was isolated and identified from cheese. Through single-factor tests and orthogonal array design, optimal fermentation conditions were established, achieving a protein content of 54.56 ± 0.05% and a protein yield of 6.12 ± 0.11 g/L in shake flask cultivation (n = 3). Phosphate (PO₄^3-) was identified as the key regulatory ion, and supplementation with potassium dihydrogen phosphate (KH₂PO₄) significantly enhanced amino acid accumulation. Transcriptomic analysis revealed that KH₂PO₄ reprograms central carbon metabolism to support amino acid biosynthesis. These findings provide an experimental and theoretical basis for the industrial application and genetic improvement of this strain in microbial protein production.