Prolonged bioproduction of tryptophan by immobilized E.coli cells using sugar beet molasses. (Article Uncorrected Proof)

Sugar beet molasses is a well-known، inexpensive and available carbon source for microbial cell growth. Its sugar components are used to produce energy for microbial growth and non-sugar components، especially nitrogen components، have important roles in improvement of cell growth. On the other hand، immobilization of whole cell is establishment and physical limitation of intact cells in specific space that keeps their catalytic activity and provides the possibility of reuse of the cells. This technique allows continuous and accelerated biological processes. It also improves production efficiency and quality and simplifies recycling of product. Immobilized living cells، as controlled catalysts، are able to perform one-step enzymatic reaction and continuous fermentative processes. In this research، E. coli cells were immobilized in calcium alginate hydrogels and using sugar beet molasses as carbon source، were applied for tryptophan production reaction in the presence of its precursors، serine and indole. In comparison between free biocatalysts and immobilized bacterial cells that entrapped in alginate gels، indicated that larger amounts of amino acids (about 42/9%) can produce in calcium alginate. Also the production reaction was followed up for 9 sequential cycles، and results showed that the cells could produce tryptophan amino acid under above conditions. Use of sugar beet molasses (by-product of agriculture industries) for growth of microbial cells and tryptophan production، causes decrease in production cost and more economical production of tryptophan by immobilized E. coli.