Abstract: Cell biomass and pH of Geobacillus stearothermophilus CHB1 in culture medium were used as indices in the optimization study.The results indicated that different carbon and nitrogen sources significantly affected the microbial growth.By using orthogonal experimentation design,the optimal medium composition was obtained: 0.5% beef extract,0.9% soy peptone,0.2% NaCl,0.1% K₂HPO₄ and 0.075% KH₂PO₄.It was found that the biomass resulted from the newly formulated medium was ten times greater than that from the standard fermentation medium.

Key words: Geobacillus stearothermophilus CHB1, fermentation medium, optimization