Continuous production of L ‐isoleucine using immobilized growing Serratia marcescens cells

An immobilized growing cell system was applied to the continuous L‐isoleucine production by Serratia marcescens. In the new immobilized‐cell systems using the carrageenan gel method. S. marcescens cells in the gel required nutrients and oxygen for growth, and the numbers of living cells per milliliter of gel increased to the levels of that of free cells in the liquid medium. This immobilized growing cell system exhibited high and stable activity for isoleucine production under steady‐state conditions. Continuous isoleucine production was carried out by feeding the nutrient medium under aeration into a fluidized bed reactor containing the immobilized cells. In the continuous operation, an efficient production was maintained by automatically controlling the pH of the reaction mixture at 7.5. The productivity of isoleucine increased using multibed reactors. In a two‐bed reactor system, the effluent L‐isoleucine concentration reached 4.5 mg/ml at a retention time of 10 hr, and a steady state was maintained for longer than 30 days.