The effects of CO2 on growth and product formation in submerged cultures have been investigated in various microorganisms, and the controversy results were always encountered. Researches of Gill and Lacoursiere had revealed that cell growth and metabolism of Pseudomonas fluorescens and Escherichia coli could be stimulated at low dissolved CO2level not more than 100 mm Hg pressure or 5% inlet gas phase respectively, while it could be greatly inhibited by the increased CO2 concentration