Scaling up of levan yield in Bacillus subtilis M and cytotoxicity study on levan and its derivatives by Ragab, Tamer I. M., Abd. Malek, Roslinda, Elsehemy, Islam A., Farag, Mohamed M. S., Salama, Bassem M., Abd. EL-Baseer, Mohamed A., Gamal-Eldeen, Amira M., El Enshasy, Hesham A., Esawy, Mona A.